INFLAMMATION- Full chapter exam ready notes

 

INFLAMMATION

Detailed Medical Undergraduate Examination Notes

Pathology • Physiology • Immunology • Clinical Correlation

1. Introduction

Inflammation is a protective response of living, vascularized tissues to infection, tissue injury, or other harmful stimuli.

Its fundamental purpose is to:

1. Recognize and eliminate the injurious agent
2. Remove damaged and necrotic tissue
3. Recruit immune cells and plasma proteins to the site of injury
4. Limit the spread of infection or injury
5. Initiate tissue repair and restoration of homeostasis

Inflammation is therefore not itself a disease. It is a defensive biological response that becomes harmful when it is excessive, prolonged, inappropriate, or directed against the body's own tissues.

The inflammatory response involves coordinated changes in:

• Blood vessels
• Endothelial cells
• Leukocytes
• Plasma proteins
• Extracellular matrix
• Resident tissue cells
• Soluble chemical mediators

Inflammation is closely linked to innate immunity. Innate immune mechanisms recognize conserved microbial structures and signals released from injured cells, rapidly initiating vascular and cellular responses. (NCBI)

2. Definition

Standard definition

Inflammation is a protective response of vascularized living tissue to injury or infection that brings immune cells, plasma proteins and other mediators from the circulation to the site of injury, with the objective of eliminating the offending agent, removing damaged tissue and initiating repair.

The classic inflammatory response includes:

Recognition → vascular response → leukocyte recruitment → elimination of the offending agent → termination → repair

3. Why Does Inflammation Occur?

The body must distinguish between:

• Normal tissue
• Infectious organisms
• Injured cells
• Necrotic cells
• Foreign substances
• Potentially harmful environmental agents

Inflammation is triggered when tissue-resident and circulating immune systems detect danger signals. Two major categories of molecular signals are important.

A. PAMPs

Pathogen-associated molecular patterns

These are conserved molecular structures associated with microorganisms. Examples:

• Lipopolysaccharide (LPS) of Gram-negative bacteria
• Bacterial peptidoglycan
• Flagellin
• Viral nucleic acids
• Fungal components

B. DAMPs

Damage-associated molecular patterns

These are endogenous molecules released or exposed by injured or necrotic cells. Examples:

• ATP
• HMGB1
• Extracellular DNA
• Uric acid crystals
• Components of damaged extracellular matrix

PAMPs and DAMPs are recognised by pattern-recognition receptors (PRRs) on cells of the innate immune system.

Important PRRs include:

• Toll-like receptors (TLRs)
• NOD-like receptors (NLRs)
• RIG-I-like receptors
• C-type lectin receptors

TLR activation can stimulate intracellular signalling pathways involving transcription factors such as NF-κB, AP-1 and interferon regulatory factors, leading to production of inflammatory cytokines and other mediators. (NCBI)

4. Cardinal Features of Inflammation

The classical clinical features were described using Latin terms.

The five cardinal signs

Sign	Latin term	Main mechanism
Redness	Rubor	Vasodilation and increased blood flow
Heat	Calor	Increased blood flow and metabolic activity
Swelling	Tumor	Accumulation of inflammatory fluid
Pain	Dolor	Mediators such as bradykinin and PGE₂
Loss of function	Functio laesa	Pain, swelling and tissue damage

The first four classical features are especially prominent in superficial acute inflammation. Internal inflammation may not display all of them externally. (NCBI)

5. Major Types of Inflammation

The two principal forms are:

1. Acute inflammation
2. Chronic inflammation

A transitional or subacute pattern may occur clinically, but the fundamental pathological classification is acute versus chronic.

6. Acute Inflammation

Definition

Acute inflammation is the rapid, relatively short-duration inflammatory response to tissue injury or infection.

It usually develops within: minutes to hours and generally lasts: hours to a few days.

The characteristic cellular infiltrate is predominantly: Neutrophils

Acute inflammation is characterized by:

• Rapid onset
• Vasodilation
• Increased vascular permeability
• Exudation of protein-rich fluid
• Neutrophil recruitment
• Possible formation of pus
• Usually limited duration

(NCBI)

7. Causes Of Acute Inflammation

Acute inflammation can be produced by numerous stimuli.

A. Infections

Examples:

• Bacterial infections
• Viral infections
• Fungal infections
• Parasitic infections

B. Physical agents

Examples:

• Trauma
• Burns
• Frostbite
• Radiation
• Mechanical injury

C. Chemical agents

Examples:

• Acids
• Alkalis
• Toxins
• Irritant chemicals

D. Tissue necrosis

Any form of cell death may induce inflammation. Examples:

• Ischaemic necrosis
• Traumatic necrosis
• Toxic injury

E. Foreign bodies

Examples:

• Splinters
• Sutures
• Dust particles
• Crystals

F. Immune reactions

Examples:

• Hypersensitivity reactions
• Autoimmune diseases
• Allergic reactions

8. Main Components of Acute Inflammation

Acute inflammation consists of two closely interconnected components:

1. Vascular changes

2. Cellular changes

The overall sequence is:

Injury → mediator release → vasodilation → increased vascular permeability → exudation → leukocyte recruitment → leukocyte activation → elimination of stimulus → resolution/repair

9. Vascular Changes in Acute Inflammation

Vascular changes occur early and are essential for bringing plasma proteins and leukocytes to the site of injury. They can be divided into:

1. Changes in vascular calibre and blood flow
2. Increased vascular permeability
3. Formation of inflammatory exudate
4. Stasis of blood flow

9.1 Transient Vasoconstriction

Immediately following a very mild injury, there may be a brief: Vasoconstriction. This usually lasts only a few seconds. It is followed by vasodilation.

10. Vasodilation

The next major vascular event is: Vasodilation of arterioles. This results in:

• Increased blood flow
• Redness
• Heat

The process subsequently involves opening of additional capillary beds.

Important mediator: Histamine

Other mediators can also contribute. The increased blood flow is responsible for the classical signs: Rubor + Calor

Vasodilation is one of the earliest characteristic vascular events in acute inflammation. (NCBI)

11. Increased Vascular Permeability

This is one of the most important events of acute inflammation. Normally, endothelial cells form a selective barrier between blood and tissues. During inflammation, this barrier becomes more permeable.

Consequently:

• Plasma proteins leave the circulation
• Fluid leaves blood vessels
• Leukocytes subsequently migrate into tissues

The accumulation of fluid produces: Oedema

12. Mechanisms of Increased Vascular Permeability

Several mechanisms can increase endothelial permeability.

A. Endothelial cell contraction

This is the most common mechanism of immediate transient responses. Inflammatory mediators such as:

• Histamine
• Bradykinin
• Leukotrienes

cause endothelial cells to contract and create gaps between them. This occurs mainly in: Post-capillary venules. The response is rapid and short-lived.

B. Direct endothelial injury

Severe injury can directly damage endothelial cells.

Examples:

• Severe burns
• Severe trauma
• Toxins

This produces leakage of fluid and proteins. The injury may be immediate and sustained.

C. Delayed prolonged leakage

Certain injuries produce delayed endothelial damage. Examples:

• Ultraviolet radiation
• Mild thermal injury

Leakage may develop after a delay and persist for several hours.

D. Leukocyte-mediated endothelial injury

Activated leukocytes can themselves damage endothelial cells by releasing:

• Reactive oxygen species
• Proteases
• Other inflammatory mediators

This may increase vascular leakage.

E. Increased transcytosis

Vesicular transport of proteins across endothelial cells may increase in response to certain mediators.

F. Leakage from newly formed vessels

Newly formed vessels are relatively immature and may remain more permeable. This is particularly important during:

• Chronic inflammation
• Wound healing
• Angiogenesis

13. Exudate And Transudate

This is a very important examination distinction.

Exudate

An exudate is an inflammatory extravascular fluid with:

• High protein content
• Increased specific gravity
• Numerous inflammatory cells, depending on the process

It forms because inflammatory mediators increase vascular permeability. Example: Bacterial pneumonia may produce a protein-rich inflammatory exudate in alveoli.

Transudate

A transudate is a relatively protein-poor fluid produced primarily because of:

• Increased hydrostatic pressure
• Reduced plasma oncotic pressure

There is usually no major primary increase in vascular permeability.

Examples

• Congestive heart failure
• Severe hypoalbuminaemia

Exudate vs Transudate

Feature	Exudate	Transudate
Mechanism	Increased vascular permeability	Hydrostatic/oncotic imbalance
Protein	High	Low
Specific gravity	Relatively high	Relatively low
Inflammatory cells	Often present	Usually absent or few
Inflammation	Usually associated	Usually not primary
Example	Bacterial inflammation	Heart failure

Exam point

-Exudate = inflammation

-Transudate = haemodynamic imbalance

14. Stasis

Initially, vasodilation increases blood flow. However, as fluid leaves the vessels:

• Intravascular plasma volume decreases
• Blood becomes more concentrated
• Viscosity increases
• Blood flow slows

This produces: Stasis.  As blood flow slows, leukocytes move toward the endothelial surface. This process is called: Margination

15. Leukocyte Recruitment

Recruitment of leukocytes from blood into injured tissue is a fundamental feature of inflammation. The major stages are:

Margination → Rolling → Adhesion → Transmigration → Chemotaxis → Activation → Phagocytosis

16. Margination

Under normal conditions, erythrocytes occupy the central axial stream of blood while leukocytes tend to remain closer to the vessel wall.

During inflammation:

• Blood flow slows
• Leukocytes move toward the endothelial surface

This is: Margination

17. Rolling

Marginalized leukocytes attach transiently to endothelial cells and detach repeatedly. This produces: Rolling

The principal adhesion molecules involved are:

• P-selectin
• E-selectin

Selectins mediate weak, transient interactions.

Important sources

P-selectin

Stored in:

• Endothelial Weibel-Palade bodies
• Platelet granules

It can rapidly appear on the endothelial surface after stimulation.

E-selectin

Synthesized by activated endothelial cells in response to inflammatory cytokines such as:

• TNF
• IL-1

(NCBI)

18. Adhesion

Rolling leukocytes become activated by chemokines displayed on endothelial surfaces. This activates leukocyte integrins. Integrins then bind strongly to endothelial adhesion molecules. Important endothelial molecules include:

• ICAM-1
• VCAM-1

Important leukocyte integrins include:

• LFA-1
• Mac-1
• VLA-4

This produces: Firm adhesion

Cytokines such as TNF and IL-1 increase endothelial expression of adhesion molecules.

19. Transmigration

After firm adhesion, leukocytes cross the endothelial barrier. This process is called:

Diapedesis or transmigration

It occurs predominantly through: Post-capillary venules

An important molecule involved is: PECAM-1 (CD31)

PECAM-1 is expressed on:

• Leukocytes
• Endothelial cells

It facilitates passage of leukocytes between endothelial cells. (NCBI)

20. Chemotaxis

After entering the extravascular tissue, leukocytes move toward the site of injury. This directed movement is called: Chemotaxis

The movement occurs along a chemical concentration gradient.

Major chemotactic substances

Exogenous

• Bacterial products

Endogenous

• C5a
• LTB₄
• Chemokines, especially CXCL8/IL-8

These substances guide leukocytes toward the inflammatory focus.

21. Leukocyte Activation

Once leukocytes reach the inflammatory site, they become activated. Activated leukocytes:

• Phagocytose microorganisms
• Kill microorganisms
• Remove necrotic tissue
• Release cytokines
• Release proteases
• Generate reactive oxygen species

These mechanisms are protective but can also cause collateral tissue injury.

22. Phagocytosis

Phagocytosis consists of three major stages:

1. Recognition and attachment

2. Engulfment

3. Killing and degradation

22.1 Recognition and attachment

Leukocytes recognise:

• Microbial surface structures
• Dead cells
• Foreign substances

Recognition becomes much more efficient when microorganisms are coated by:

Opsonins

Important opsonins include:

• IgG
• C3b
• Collectins

The leukocyte receptors recognise these molecules.

23. Engulfment

The leukocyte extends pseudopods around the target. The target becomes enclosed within a: Phagosome

The phagosome then fuses with lysosomal granules to form a: Phagolysosome

24. Microbial Killing

Microorganisms are killed by:

A. Reactive oxygen species

B. Reactive nitrogen species

C. Lysosomal enzymes

Respiratory burst

Activated phagocytes increase oxygen consumption and generate reactive oxygen species. An important enzyme is:

NADPH oxidase

It generates superoxide. Superoxide can subsequently give rise to:

• Hydrogen peroxide
• Other reactive oxygen intermediates

25. Myeloperoxidase System

A particularly powerful antimicrobial mechanism in neutrophils involves: Myeloperoxidase (MPO)

MPO uses:

• Hydrogen peroxide
• Chloride ions

to generate: Hypochlorous acid (HOCl).  HOCl is highly effective in killing microorganisms.

MPO + H₂O₂ + Cl⁻ → HOCl

The system is sometimes compared with the antimicrobial action of bleach because hypochlorous acid is a powerful oxidizing agent.

26. Reactive Nitrogen Species

Activated macrophages can produce: Nitric oxide (NO). NO can react with superoxide to form: Peroxynitrite, which has strong antimicrobial and tissue-damaging effects.

27. Leukocyte-Mediated Tissue Injury

The same mechanisms used to destroy microorganisms can damage host tissues.

Important substances include:

• Lysosomal proteases
• ROS
• Reactive nitrogen species
• Matrix metalloproteinases

This is an important pathological principle:

Inflammation protects the host but may itself produce tissue injury.

Examples include:

• Acute respiratory distress syndrome
• Chronic inflammatory diseases
• Immune-mediated tissue injury
• Some forms of glomerulonephritis

28. Important Cellular Events in Acute Inflammation

Neutrophils

Neutrophils are the predominant cells during most acute inflammatory reactions.

They:

• Arrive early
• Phagocytose microbes
• Release antimicrobial substances
• Generate ROS
• Produce inflammatory mediators

Monocytes/macrophages

Monocytes generally appear later and differentiate into macrophages in tissues.

Actions of Macrophages:

• Phagocytose
• Produce cytokines
• Present antigens
• Participate in resolution
• Participate in tissue repair

29. Why Are Neutrophils First?

Neutrophils:

• Are abundant in circulating blood
• Respond rapidly to chemotactic signals
• Have strong phagocytic capacity
• Contain numerous antimicrobial granules
• Are adapted for rapid microbial killing

Therefore:

Acute inflammation → predominantly neutrophils

30. Chemical Mediators of Inflammation

Inflammatory mediators are substances that initiate, amplify, regulate or terminate inflammatory responses. They may be:

1.     Cell-derived

2.     Plasma-derived

31. Cell-Derived Mediators

Important sources include:

• Mast cells
• Platelets
• Neutrophils
• Macrophages
• Endothelial cells
• Lymphocytes

Major mediators include:

• Histamine
• Prostaglandins
• Leukotrienes
• Platelet-activating factor
• Cytokines
• Chemokines
• Nitric oxide
• Reactive oxygen species
• Lysosomal enzymes

32. Plasma-Derived Mediators

Important systems include:

1.     Complement system

2.     Kinin system

3.     Coagulation system

4.     Fibrinolytic system

33. Histamine

Histamine is one of the most important early mediators of acute inflammation.

Major sources

• Mast cells
• Basophils
• Platelets

Major actions

Histamine causes:

• Arteriolar vasodilation
• Increased venular permeability
• Endothelial contraction
• Bronchoconstriction in certain settings

It contributes importantly to:

• Redness
• Swelling
• Allergic reactions

34. Prostaglandins

Prostaglandins are derived from: Arachidonic acid

The pathway begins with phospholipase A₂-mediated release of arachidonic acid from membrane phospholipids. Arachidonic acid is then metabolized through: Cyclooxygenase Pathway producing prostaglandins and thromboxanes.

Important prostaglandins

PGE₂

Major actions:

• Pain
• Fever
• Vasodilation

PGI₂ (prostacyclin)

Major actions:

• Vasodilation
• Inhibition of platelet aggregation

PGD₂

Important in:

• Vasodilation
• Allergic responses

TXA₂

Major actions:

• Platelet aggregation
• Vasoconstriction

35. Leukotrienes

Leukotrienes are also derived from arachidonic acid. The major pathway is: 5-lipoxygenase pathway

Important leukotrienes include:

LTB₄

Strong:

• Chemotactic agent
• Leukocyte activator

LTC₄, LTD₄ and LTE₄

Cause:

• Bronchoconstriction
• Increased vascular permeability
• Mucus secretion

They are particularly important in:

• Asthma
• Allergic inflammation

(NCBI)

36. Platelet-Activating Factor

PAF can be produced by:

• Leukocytes
• Platelets
• Endothelial cells
• Mast cells

It can cause:

• Platelet activation
• Vasodilation
• Increased vascular permeability
• Leukocyte adhesion
• Leukocyte chemotaxis
• Bronchoconstriction

37. Cytokines

Cytokines are signalling proteins produced by many cells. Important inflammatory cytokines include:

• TNF
• IL-1
• IL-6
• IL-12
• IL-17
• IFN-γ

38. TNF and IL-1

These are major cytokines in inflammation.

Major actions

They:

• Activate endothelium
• Increase adhesion molecule expression
• Promote leukocyte recruitment
• Stimulate cytokine production
• Contribute to fever
• Promote systemic inflammatory responses

TNF is particularly important in severe systemic inflammation.

39. IL-6

IL-6 has major systemic effects.

It promotes:

• Acute-phase protein synthesis by the liver
• Fever
• Systemic inflammatory responses
• B-cell-related immune functions

The IL-6 pathway is an important link between local inflammation and systemic acute-phase responses. (NCBI)

40. Chemokines

Chemokines are cytokines whose major function is: Leukocyte recruitment and migration

Examples:

• CXCL8/IL-8 → neutrophils
• CCL2 → monocytes
• Other chemokines → specific leukocyte populations

They establish chemical gradients that guide leukocytes toward inflamed tissues.

41. Complement System

Complement consists of plasma proteins that participate in innate and adaptive immunity.

Three major activation pathways are:

1. Classical pathway
2. Alternative pathway
3. Lectin pathway

Important inflammatory complement fragments include: C3a and C5a. They are called:

Anaphylatoxins

They promote inflammatory responses, including mast-cell activation.

C5a

C5a is particularly important because it:

• Attracts neutrophils
• Activates leukocytes
• Promotes inflammatory responses

C3b

C3b acts as an: Opsonin.  It enhances phagocytosis.

Membrane attack complex

C5b–C9 forms: MAC

The membrane attack complex can create pores in susceptible target cell membranes.

42. Bradykinin

Bradykinin is generated through the: Kinin system

It produces:

• Pain
• Vasodilation
• Increased vascular permeability
• Smooth muscle effects

Bradykinin = important mediator of pain and vascular permeability.

43. Nitric Oxide

Nitric oxide is produced by nitric oxide synthases. It has several effects, including:

• Vasodilation
• Modulation of leukocyte adhesion
• Microbicidal activity in activated macrophages

NO can therefore have both protective and regulatory functions in inflammation. (NCBI)

44. Inflammatory Mediators

Mediator	Major source	Major action
Histamine	Mast cells	Vasodilation, permeability
PGE₂	Leukocytes, mast cells, other cells	Pain, fever, vasodilation
PGI₂	Endothelium	Vasodilation, inhibits platelet aggregation
TXA₂	Platelets	Vasoconstriction, platelet aggregation
LTB₄	Leukocytes	Chemotaxis
LTC₄/LTD₄/LTE₄	Leukocytes, mast cells	Bronchoconstriction, permeability
TNF	Macrophages	Endothelial activation, systemic effects
IL-1	Macrophages	Endothelial activation, fever
IL-6	Macrophages, other cells	Acute-phase response
CXCL8/IL-8	Macrophages/endothelium	Neutrophil recruitment
C3a	Complement	Mast-cell activation
C5a	Complement	Chemotaxis and leukocyte activation
C3b	Complement	Opsonisation
Bradykinin	Plasma kinin system	Pain, permeability, vasodilation
PAF	Leukocytes, platelets, endothelium	Platelet/leukocyte activation
NO	Endothelium/macrophages	Vasodilation; antimicrobial effects

45. Outcomes of Acute Inflammation

Acute inflammation may have four major outcomes.

1. Complete resolution

The tissue returns to its normal state.

2. Healing by fibrosis

If tissue destruction is substantial or regeneration is impossible, connective tissue replaces the damaged tissue.

3. Abscess formation

A localized collection of pus develops.

4. Progression to chronic inflammation

If the offending stimulus persists, acute inflammation may become chronic.

46. Resolution of Acute Inflammation

Resolution is an active biological process, not simply cessation of inflammation. Important events include:

• Removal of the offending stimulus
• Clearance of inflammatory cells
• Removal of excess fluid
• Removal of dead cells and debris
• Restoration of vascular permeability
• Restoration of tissue architecture

Anti-inflammatory mediators and specialized pro-resolving mediators help terminate inflammation.

47. Chronic Inflammation

Definition

Chronic inflammation is a prolonged inflammatory response in which active inflammation, tissue injury and attempts at repair occur simultaneously.

It may persist for: Weeks, months or years

The cellular infiltrate is predominantly:

• Macrophages
• Lymphocytes
• Plasma cells

rather than neutrophils. (NCBI)

48. Causes of Chronic Inflammation

A. Persistent infections

Examples:

• Mycobacteria
• Certain fungi
• Some parasites

B. Autoimmune diseases

Examples:

• Rheumatoid arthritis
• Systemic lupus erythematosus

C. Prolonged exposure to toxic agents

Examples:

• Silica
• Certain environmental particles

D. Persistent foreign bodies

Examples:

• Sutures
• Splinters
• Other foreign materials

E. Long-standing metabolic disorders

Some metabolic diseases are associated with chronic low-grade inflammation.

49. Morphological Features of Chronic Inflammation

The three classical pathological features are:

1. Mononuclear cell infiltration

Predominantly:

• Macrophages
• Lymphocytes
• Plasma cells

2. Tissue destruction

Caused by:

• Persistent injury
• Microbial products
• Inflammatory mediators
• Leukocyte products

3. Repair

Characterized by:

• Angiogenesis
• Fibrosis
• Extracellular matrix deposition

50. Macrophages in Chronic Inflammation

Macrophages are central to chronic inflammation. They perform several functions.

A. Phagocytosis

They remove:

• Microorganisms
• Necrotic cells
• Cellular debris

B. Cytokine production

They produce:

• TNF
• IL-1
• IL-6
• Chemokines

C. Tissue injury

They release:

• ROS
• Proteases
• Cytokines

D. Repair

They can release:

• Growth factors
• Fibrogenic mediators
• Angiogenic factors

Thus, macrophages can both: Destroy tissue and Promote repair

51. Lymphocytes in Chronic Inflammation

Lymphocytes include:

• T cells
• B cells
• Plasma cells

T lymphocytes can activate macrophages and influence the inflammatory response through cytokines.

Macrophages, in turn, present antigens and produce cytokines that influence lymphocyte responses.

This produces a: Macrophage–lymphocyte interaction which can sustain chronic inflammation.

52. Plasma Cells

Plasma cells are differentiated B lymphocytes that produce antibodies. They are particularly prominent in chronic inflammatory reactions associated with:

• Persistent infections
• Autoimmune diseases
• Chronic antigenic stimulation

53. Eosinophils

Eosinophils are important particularly in:

• Parasitic infections
• Allergic diseases

They contain granules rich in proteins that can damage parasites but can also damage host tissues. Examples of eosinophil-associated conditions:

• Bronchial asthma
• Allergic rhinitis
• Helminthic infections

54. Mast Cells

Mast cells are tissue-resident immune cells. They contain preformed mediators such as:

Histamine

They also generate:

• Leukotrienes
• Prostaglandins
• Cytokines

Mast cells are important in:

• Immediate hypersensitivity
• Allergic reactions
• Some chronic inflammatory diseases

55. Acute Vs Chronic Inflammation

Feature	Acute inflammation	Chronic inflammation
Onset	Rapid	Slow/prolonged
Duration	Hours–days	Weeks–years
Main cells	Neutrophils	Macrophages, lymphocytes, plasma cells
Vascular changes	Prominent	Usually less prominent
Oedema	Common	Variable
Tissue destruction	Usually limited	Often progressive
Repair/fibrosis	Usually limited	Prominent
Typical example	Acute bacterial infection	Tuberculosis/rheumatoid arthritis

Distinction

Acute = neutrophils

Chronic = mononuclear cells + tissue destruction + repair

\56. Granulomatous Inflammation

Granulomatous inflammation is a distinctive form of chronic inflammation characterized by formation of:

Granulomas

A granuloma is a focal collection of activated macrophages, usually with:

• Epithelioid cells
• Multinucleated giant cells
• Surrounding lymphocytes

57. Causes of Granulomas

Important causes include:

Infectious

• Mycobacterium tuberculosis
• Some fungal infections
• Certain bacterial infections

Non-infectious

• Sarcoidosis
• Foreign bodies
• Crohn disease

58. Epithelioid Cells

Activated macrophages may transform into:

Epithelioid cells

They are:

• Enlarged
• Polygonal
• Abundant cytoplasm

They resemble epithelial cells, hence the name.

59. Giant Cells

Macrophages may fuse to form: Multinucleated giant cells. Two important patterns include:

Langhans giant cells

Nuclei are arranged toward the periphery.

Foreign-body giant cells

Nuclei are more irregularly distributed throughout the cytoplasm.

Important examination caution

The term Langhans giant cell is associated with granulomatous inflammation and is different from Langerhans cells, which are dendritic antigen-presenting cells.

60. Granuloma In Tuberculosis

A typical tuberculous granuloma may contain:

• Central caseous necrosis
• Epithelioid cells
• Langhans giant cells
• Surrounding lymphocytes

This is classically called a: Caseating granuloma

However, granuloma morphology must always be interpreted in clinical and microbiological context.

61. Systemic Effects of Inflammation

Inflammation is not always restricted to the local tissue. Major systemic manifestations include:

• Fever
• Leukocytosis
• Acute-phase protein production
• Increased heart rate
• Malaise
• Anorexia
• Sleepiness

Severe systemic inflammation may produce:

• Hypotension
• Disseminated intravascular coagulation
• Organ dysfunction
• Shock

62. Fever

Fever occurs when inflammatory mediators alter the hypothalamic temperature set point. Important endogenous pyrogens include:

• IL-1
• TNF
• IL-6

These stimulate pathways leading to increased production of: PGE₂ in the hypothalamic region. The temperature set point rises, producing:

• Vasoconstriction
• Shivering
• Increased heat production

until the new set point is reached.

63. Acute-Phase Response

Inflammatory cytokines, especially: IL-6, stimulate the liver to synthesize acute-phase proteins. Important acute-phase proteins include:

• C-reactive protein
• Fibrinogen
• Serum amyloid A

64. C-Reactive Protein

CRP is an important acute-phase protein. It increases during systemic inflammation. Clinical uses include:

• Detection of inflammation
• Monitoring inflammatory activity
• Monitoring response to treatment

CRP is not disease-specific.

65. ESR

The erythrocyte sedimentation rate may increase during inflammation. Inflammatory cytokines stimulate hepatic production of:

Fibrinogen

Increased fibrinogen promotes rouleaux formation, increasing the sedimentation rate of erythrocytes.

Thus: Inflammation → ↑ fibrinogen → rouleaux → ↑ ESR

ESR is also non-specific.

66. Leukocytosis

Inflammation frequently produces an increase in circulating leukocytes. The pattern can provide clues to the cause.

Neutrophilia

Commonly associated with:

• Acute bacterial infection
• Tissue necrosis
• Some inflammatory disorders

Lymphocytosis

Commonly associated with:

• Many viral infections
• Some chronic infections

Eosinophilia

Associated with:

• Parasitic infections
• Allergic disorders

Monocytosis

May occur in:

• Chronic infections
• Some inflammatory diseases

67. Leukocyte Count and Inflammation

A useful exam association is:

Bacterial infection → neutrophilia

Viral infection → lymphocytosis

Helminthic infection/allergy → eosinophilia

Chronic inflammation → monocytosis may occur

These are patterns, not absolute rules.

68. Systemic Inflammatory Response

When inflammatory mediators enter the circulation in large quantities, inflammation can become systemic. This can occur in:

• Severe bacterial infection
• Major tissue injury
• Severe pancreatitis
• Extensive burns

69. Sepsis And Systemic Inflammation

Excessive systemic inflammatory activation can cause:

• Vasodilation
• Increased vascular permeability
• Hypotension
• Microvascular dysfunction
• Coagulation abnormalities
• Tissue hypoperfusion
• Organ dysfunction

Severe dysregulated inflammation may therefore become life-threatening.

70. Beneficial Effects of Inflammation

Inflammation is protective because it:

1. Eliminates pathogens

2. Removes dead cells

3. Removes foreign substances

4. Limits spread of infection

5. Initiates tissue repair

6. Activates adaptive immunity

Innate inflammatory mechanisms can help initiate subsequent adaptive immune responses. (NCBI)

71. Harmful Effects of Inflammation

Inflammation becomes pathological when:

• Excessive
• Prolonged
• Inappropriately activated
• Directed against self-tissues

Consequences include:

• Tissue destruction
• Fibrosis
• Organ dysfunction
• Pain
• Oedema
• Airway obstruction
• Vascular injury

Examples:

• Rheumatoid arthritis
• Asthma
• Inflammatory bowel disease
• Atherosclerosis
• Autoimmune diseases

72. Inflammation and Tissue Repair

Inflammation and repair are closely linked. After removal of the injurious agent: Resolution may occur. If significant tissue damage has occurred: Repair begins. Repair can involve:

• Regeneration
• Fibrosis

Macrophages play a central role in coordinating the transition from inflammation to repair.

73. Regeneration vs Repair by Fibrosis

Regeneration

Damaged cells are replaced by cells of the same type. The original tissue architecture may be restored.

Fibrosis

Damaged tissue is replaced partly or largely by:

Connective tissue

Fibrosis is more likely when:

• Tissue destruction is extensive
• The tissue has limited regenerative capacity
• The extracellular matrix is severely damaged
• Inflammation is persistent

74. Important Pathological Terms

Serous inflammation

Produces a relatively clear, protein-containing fluid. Example: Skin blister after a burn

Fibrinous inflammation

Produces abundant fibrin. Commonly occurs on: Serosal surfaces

Examples:

• Fibrinous pericarditis
• Fibrinous pleuritis

Suppurative inflammation

Produces: Pus. Pus contains:

• Neutrophils
• Necrotic debris
• Microorganisms, often bacteria

Abscess

A localized collection of pus within tissue.

Ulcer

A local defect or excavation of the surface of an organ or tissue caused by loss of necrotic inflammatory tissue.

Common examples:

• Peptic ulcer
• Skin ulcer

75. Lymphatic Role In Inflammation

The lymphatic system has an important role in inflammation.

Inflammation increases:

• Lymph flow
• Drainage of interstitial fluid
• Transport of antigens
• Transport of inflammatory cells and debris

Lymphatic drainage can therefore help remove inflammatory fluid, but lymphatics can also provide a route for spread of microorganisms or tumour cells. (NCBI)

76. Molecular Sequence of Acute Inflammation

A useful way to remember the entire process is:

STEP 1

Tissue injury/infection

↓

STEP 2

Recognition of PAMPs/DAMPs

↓

STEP 3

Activation of resident cells

↓

STEP 4

Release of inflammatory mediators

↓

STEP 5

Vasodilation

↓

STEP 6

Increased vascular permeability

↓

STEP 7

Exudation and oedema

↓

STEP 8

Stasis and margination

↓

STEP 9

Rolling

↓

STEP 10

Firm adhesion

↓

STEP 11

Transmigration

↓

STEP 12

Chemotaxis

↓

STEP 13

Phagocytosis

↓

STEP 14

Microbial killing

↓

STEP 15

Termination/resolution or progression

↓

STEP 16

Repair

77. Leukocyte Recruitment — One-Line Memory

M → R → A → T → C → P → K

Margination
→ Rolling
→ Adhesion
→ Transmigration
→ Chemotaxis
→ Phagocytosis
→ Killing

This sequence is highly useful for viva and theory examinations.

78. Selectins vs Integrins

Feature	Selectins	Integrins
Main function	Rolling	Firm adhesion
Binding	Low affinity	High affinity after activation
Examples	E-selectin, P-selectin	LFA-1, Mac-1, VLA-4
Location	Mainly endothelial/leukocyte surfaces	Mainly leukocytes
Important endothelial ligands	Sialyl-Lewis X-related structures	ICAM-1, VCAM-1

Memory aid

Selectins → Slow down / Select

Integrins → Immovably attach

79. Important Adhesion Molecules

E-selectin

Activated endothelial cells → leukocyte rolling

P-selectin

Endothelial cells and platelets → leukocyte rolling

ICAM-1

Endothelial cells → leukocyte integrins

VCAM-1

Endothelial cells → leukocyte integrins

PECAM-1/CD31

Leukocytes + endothelial cells → transmigration

80. Major Chemotactic Agents

Remember:

C5a + LTB₄ + CXCL8

These are major endogenous chemotactic mediators. Bacterial products are important exogenous chemotactic agents.

81. Major Opsonins

Remember: IgG + C3b

Major opsonins include:

• IgG
• C3b
• Certain collectins

Opsonization facilitates recognition and ingestion by phagocytes.

82. Acute Inflammation: Exam-Ready Flowchart

Injury

↓

Release of inflammatory mediators

↓

Arteriolar vasodilation

↓

Increased blood flow

↓

Increased vascular permeability

↓

Protein-rich exudate

↓

Oedema

↓

Haemoconcentration and stasis

↓

Margination

↓

Rolling

↓

Firm adhesion

↓

Transmigration

↓

Chemotaxis

↓

Phagocytosis

↓

Microbial killing

↓

Resolution / fibrosis / abscess / chronic inflammation

83. Acute Vs Chronic Inflammation- Rapid Revision

Acute inflammation

• Rapid
• Short duration
• Exudation
• Oedema
• Neutrophils
• Prominent vascular changes

Chronic inflammation

• Prolonged
• Macrophages
• Lymphocytes
• Plasma cells
• Tissue destruction
• Angiogenesis
• Fibrosis

84. Important Clinical Correlations

Appendicitis

Acute inflammation of the appendix.

Histologically, neutrophilic infiltration is important.

Pneumonia

Acute inflammatory exudation can fill alveolar spaces.

This interferes with gas exchange.

Cellulitis

Diffuse acute inflammation of skin and subcutaneous tissue, commonly associated with bacterial infection.

Abscess

Localised suppurative inflammation.

Tuberculosis

Classically produces chronic granulomatous inflammation.

Rheumatoid arthritis

Chronic immune-mediated inflammation of joints.

Asthma

Inflammatory airway disease involving multiple inflammatory cells and mediators, with prominent roles for mast cells, eosinophils and T lymphocytes in many forms.

Atherosclerosis

A chronic inflammatory disease of the arterial wall involving macrophages, lymphocytes, endothelial dysfunction and lipid accumulation.

85. Inflammation and NSAIDS

Arachidonic acid metabolism is clinically important because several anti-inflammatory drugs act on this pathway.

Cyclooxygenase enzymes

COX enzymes generate prostaglandins from arachidonic acid. NSAIDs inhibit cyclooxygenase activity to varying degrees. Consequently, they reduce:

• Prostaglandin synthesis
• Pain
• Fever
• Inflammation

This provides an important pharmacological connection between pathology and clinical medicine.

86. Glucocorticoids and Inflammation

Glucocorticoids are potent anti-inflammatory agents. They suppress inflammation at multiple levels. They reduce production or action of several inflammatory mediators, including:

• Cytokines
• Chemokines
• Prostaglandins
• Leukotrienes

They also reduce leukocyte recruitment and inflammatory gene expression. Thus, glucocorticoids have broader anti-inflammatory actions than NSAIDs.

87. Important Differences: NSAIDS vs Glucocorticoids

Feature	NSAIDs	Glucocorticoids
Main action	COX inhibition	Broad transcriptional suppression
Prostaglandins	↓	↓
Leukotrienes	Relatively little direct inhibition	↓ through upstream effects
Cytokines	Limited direct effect	Strong suppression
Anti-inflammatory spectrum	Moderate	Broad
Major clinical uses	Pain, fever, inflammatory conditions	Autoimmune, allergic, inflammatory diseases

88. Termination of Inflammation

Inflammation must be controlled to prevent excessive tissue damage. Important mechanisms include:

• Removal of the inciting stimulus
• Clearance of inflammatory cells
• Anti-inflammatory cytokines
• Lipid mediators involved in resolution
• Restoration of endothelial function
• Removal of inflammatory exudate

Important anti-inflammatory mediators include:

• IL-10
• TGF-β

The balance between pro-inflammatory and anti-inflammatory mechanisms determines the outcome.

89. Important Anti-Inflammatory Cytokines

IL-10

Suppresses inflammatory responses and limits production of inflammatory cytokines by activated macrophages and other cells.

TGF-β

Has complex immunoregulatory functions and is particularly important in:

• Immune regulation
• Fibrosis
• Tissue repair

90. Inflammation as a Balance

Inflammation can be understood as a balance:

Pro-inflammatory mechanisms-

Activation → recruitment → killing → tissue injury

versus

Anti-inflammatory/resolution mechanisms-

suppression → clearance → repair → restoration

Disease can result when this balance is disturbed.

91. High-Yield Viva Questions

Q1. What is inflammation?

A protective response of vascularised living tissue to injury or infection that recruits immune cells and plasma proteins to eliminate the offending agent and initiate repair.

Q2. What are the five cardinal signs?

Rubor, calor, tumor, dolor and loss of function.

Q3. What is the predominant cell in acute inflammation?

Neutrophil.

Q4. What are the predominant cells in chronic inflammation?

Macrophages, lymphocytes and plasma cells.

Q5. What is exudate?

Protein-rich inflammatory extravascular fluid produced mainly because of increased vascular permeability.

Q6. What is transudate?

Protein-poor fluid produced mainly because of hydrostatic or oncotic pressure abnormalities.

Q7. What is chemotaxis?

Directed movement of leukocytes toward a chemical gradient.

Q8. What are major endogenous chemotactic factors?

C5a, LTB₄ and CXCL8/IL-8.

Q9. What are major opsonins?

IgG and C3b.

Q10. What is the function of P-selectin and E-selectin?

They mediate leukocyte rolling.

Q11. What is the function of integrins?

They mediate firm leukocyte adhesion to endothelium.

Q12. What is diapedesis?

Movement of leukocytes across the vascular endothelium into tissues.

Q13. What molecule participates in transmigration?

PECAM-1/CD31.

Q14. What is the major complement chemotactic factor?

C5a.

Q15. Which complement component is an important opsonin?

C3b.

Q16. Which mediator is strongly associated with pain?

Bradykinin and PGE₂ are important mediators; PGE₂ also sensitises nociceptors.

Q17. Which mediator causes fever?

PGE₂ is an important final mediator of the hypothalamic response to endogenous pyrogens.

Q18. What is the role of MPO?

It helps generate hypochlorous acid for microbial killing.

Q19. What is a granuloma?

A focal collection of activated macrophages, usually with epithelioid cells and often multinucleated giant cells, characteristic of certain chronic inflammatory reactions.

Q20. What are the three major histological features of chronic inflammation?

Mononuclear cell infiltration, tissue destruction and repair/fibrosis.

92. Very High-Yield One-Liners

1. Acute inflammation is dominated by neutrophils.
2. Chronic inflammation is dominated by macrophages and lymphocytes.
3. Histamine is an important early mediator of vasodilation and vascular permeability.
4. P-selectin and E-selectin mediate rolling.
5. Integrins mediate firm adhesion.
6. PECAM-1 is important in leukocyte transmigration.
7. C5a is a powerful chemotactic factor.
8. C3b is an important opsonin.
9. LTB₄ is chemotactic for leukocytes.
10. LTC₄, LTD₄ and LTE₄ cause bronchoconstriction and increase vascular permeability.
11. PGE₂ contributes to pain and fever.
12. Bradykinin is an important mediator of pain and increased vascular permeability.
13. TNF and IL-1 activate vascular endothelium.
14. IL-6 stimulates hepatic acute-phase protein production.
15. MPO contributes to formation of HOCl.
16. Exudate is protein-rich; transudate is protein-poor.
17. Acute inflammation usually lasts hours to days.
18. Chronic inflammation may persist for months or years.
19. Granulomatous inflammation is a specialised pattern of chronic inflammation.
20. Inflammation may end in resolution, fibrosis, abscess formation or chronic inflammation.

93. Common Examination Confusions

Confusion 1

P-selectin → rolling

not firm adhesion.

Confusion 2

Integrins → firm adhesion

not initial rolling.

Confusion 3

C3b → opsonisation

whereas:

C5a → chemotaxis

Confusion 4

LTB₄ → chemotaxis

whereas:

LTC₄/LTD₄/LTE₄ → bronchoconstriction and permeability

Confusion 5

Neutrophils → acute inflammation

Macrophages + lymphocytes → chronic inflammation

Confusion 6

Exudate ≠ transudate

Exudate is inflammatory and protein-rich; transudate primarily reflects pressure imbalance.

Confusion 7

Langhans giant cell ≠ Langerhans cell

The former is a multinucleated giant cell of granulomatous inflammation; the latter is a dendritic antigen-presenting cell.

94. Integrated Concept Map

Inflammation

Trigger

Infection / injury / necrosis / foreign body / immune reaction

↓

Recognition

PAMPs + DAMPs

↓

Sensors

PRRs

↓

Mediators

Histamine
Prostaglandins
Leukotrienes
Cytokines
Chemokines
Complement
Bradykinin

↓

Vascular response

Vasodilation
↑ permeability
Exudation
Oedema
Stasis

↓

Leukocyte recruitment

Margination
Rolling
Adhesion
Transmigration
Chemotaxis

↓

Leukocyte response

Phagocytosis
Killing
Mediator release

↓

Outcome

Resolution
OR
Fibrosis
OR
Abscess
OR
Chronic inflammation

95. Short Note: Acute Inflammation

Acute inflammation is a rapid response to tissue injury or infection that lasts from hours to a few days.

The major features are:

• Vasodilation
• Increased vascular permeability
• Protein-rich exudation
• Oedema
• Neutrophil recruitment

The sequence of leukocyte recruitment is:

Margination → rolling → adhesion → transmigration → chemotaxis → phagocytosis → killing.

Major mediators include:

• Histamine
• Prostaglandins
• Leukotrienes
• TNF
• IL-1
• Chemokines
• Complement
• Bradykinin

Possible outcomes are:

• Resolution
• Abscess
• Fibrosis
• Chronic inflammation

96. Short Note: Chronic Inflammation

Chronic inflammation is a prolonged inflammatory response characterized by:

1. Mononuclear cell infiltration
2. Tissue destruction
3. Attempts at repair

Major cells include:

• Macrophages
• Lymphocytes
• Plasma cells

Other cells may include:

• Eosinophils
• Mast cells

Chronic inflammation may result from:

• Persistent infection
• Autoimmune disease
• Persistent foreign bodies
• Prolonged toxic exposure

It may lead to:

• Fibrosis
• Organ dysfunction
• Granuloma formation

97. Short Note: Granulomatous Inflammation

Granulomatous inflammation is a specialized chronic inflammatory response characterized by collections of activated macrophages called epithelioid cells, often accompanied by multinucleated giant cells and lymphocytes.

Important causes include:

• Tuberculosis
• Fungal infections
• Sarcoidosis
• Foreign bodies
• Crohn disease

A tuberculous granuloma may show:

Caseous necrosis + epithelioid cells + Langhans giant cells + lymphocytes.

98. Exam-Oriented Summary

Inflammation is:

A protective response to injury or infection.

Acute inflammation:

Rapid + neutrophils + exudation

Chronic inflammation:

Prolonged + macrophages/lymphocytes + tissue destruction + fibrosis

Five cardinal signs:

Rubor + calor + tumor + dolor + loss of function

Leukocyte sequence:

Margination → Rolling → Adhesion → Transmigration → Chemotaxis → Phagocytosis → Killing

Rolling:

Selectins

Firm adhesion:

Integrins

Transmigration:

PECAM-1

Chemotaxis:

C5a + LTB₄ + CXCL8

Opsonisation:

IgG + C3b

Pain:

Bradykinin + PGE₂

Fever:

IL-1/TNF/IL-6 → PGE₂-mediated hypothalamic response

Bronchoconstriction:

LTC₄ + LTD₄ + LTE₄

Microbial killing:

ROS + MPO/HOCl + lysosomal enzymes + NO-related mechanisms

Chronic inflammation:

Macrophages + lymphocytes + plasma cells

Granuloma:

Activated macrophages/epithelioid cells ± giant cells

Major outcomes:

Resolution / fibrosis / abscess / chronic inflammation

99. Must-Remember Exam Table

Topic	Most important answer
Acute inflammatory cell	Neutrophil
Chronic inflammatory cell	Macrophage/lymphocyte
Early vasoactive mediator	Histamine
Rolling	Selectins
Firm adhesion	Integrins
Transmigration	PECAM-1
Major chemotactic complement fragment	C5a
Major complement opsonin	C3b
Important chemotactic leukotriene	LTB₄
Bronchoconstricting leukotrienes	LTC₄, LTD₄, LTE₄
Important pain mediator	Bradykinin
Important mediator of pain/fever	PGE₂
Major inflammatory cytokines	TNF, IL-1
Acute-phase response	IL-6
Neutrophil antimicrobial enzyme	MPO
Powerful oxidant produced by MPO system	HOCl
Main phagocytic vacuole	Phagosome
Phagosome + lysosome	Phagolysosome
Protein-rich inflammatory fluid	Exudate
Pressure-related fluid	Transudate
Specialised chronic inflammation	Granulomatous inflammation
Typical granulomatous infection	Tuberculosis
Repair-promoting chronic process	Fibrosis/angiogenesis

100. Final Concept

The most important concept to understand is that inflammation is a coordinated response, not merely swelling or redness.

At the beginning, tissue injury or infection is recognised by innate immune sensors. Resident cells then release mediators that alter the microcirculation. Blood vessels dilate and become more permeable, producing an exudate. Leukocytes are subsequently recruited through a highly organised sequence of rolling, adhesion and transmigration. They follow chemotactic gradients into the tissue, where they phagocytose and destroy pathogens and remove damaged material.

If the offending stimulus is eliminated, the response can resolve and the tissue may return toward normal. If the stimulus persists, or if the inflammatory response itself becomes dysregulated, chronic inflammation, tissue destruction, fibrosis and organ dysfunction may develop.

Thus, the central pathological principle is:

Inflammation is protective when appropriately regulated, but the same mechanisms that eliminate harmful agents can produce tissue injury when excessive or persistent.

This balance between host defence, tissue injury, resolution and repair is the fundamental concept underlying the study of inflammation in pathology and medicine.

Rapid Last-Minute Revision

Inflammation = protective response to injury/infection

Acute = neutrophils

Chronic = macrophages + lymphocytes + plasma cells

Vasodilation = redness + heat

Increased permeability = exudate + oedema

Selectins = rolling

Integrins = adhesion

PECAM-1 = transmigration

C5a = chemotaxis

C3b = opsonin

LTB₄ = chemotaxis

LTC₄/LTD₄/LTE₄ = bronchoconstriction

PGE₂ = pain + fever

Bradykinin = pain + permeability

TNF/IL-1 = endothelial activation

IL-6 = acute-phase response

MPO → HOCl = microbial killing

Chronic inflammation = inflammation + tissue destruction + repair

Granuloma = activated macrophages/epithelioid cells ± giant cells

Outcome = resolution / fibrosis / abscess / chronic inflammation

References and Standard Textbook Sources for Further Reading

1. Kumar V, Abbas AK, Aster JC, Debnath J, Das A. Robbins, Cotran & Kumar Pathologic Basis of Disease. 11th ed. Elsevier, 2025. Chapter 3: Inflammation and Repair. This is the principal pathology reference for these notes and the current standard Robbins edition. (Elsevier Shop)
2. Hall JE, Hall ME. Guyton and Hall Textbook of Medical Physiology. 14th ed. Elsevier. Chapter 34: Resistance of the Body to Infection: I. Leukocytes, Granulocytes, the Monocyte-Macrophage System, and Inflammation. (Educate)
3. Janeway CA Jr, Travers P, Walport M, et al. Immunobiology: The Immune System in Health and Disease. NCBI Bookshelf. The sections on innate immunity and induced innate responses provide the immunological basis of inflammatory recognition and leukocyte recruitment. (NCBI)
4. Hannoodee S, Nasuruddin DN. Acute Inflammatory Response. StatPearls, NCBI Bookshelf. Provides an updated review of acute inflammatory mechanisms, inflammatory mediators, complement, arachidonic-acid metabolites and cellular responses. (NCBI)
5. StatPearls. Pathology, Inflammation. NCBI Bookshelf. Provides an overview of acute and chronic inflammation, vascular responses and leukocyte recruitment. (NCBI)
6. Granger DN, Senchenkova E. Inflammation and the Microcirculation. NCBI Bookshelf. Provides detailed information on vascular responses and leukocyte–endothelial interactions during inflammation. (NCBI)
7. NCBI Bookshelf. Chronic Inflammation. Provides detailed discussion of the cellular composition, tissue destruction, repair and fibrosis associated with chronic inflammation. (NCBI)