Hypersensitivity Immunologically Mediated Tissue Injury Inflammation

Slide 1 · Hypersensitivity

Immunologically Mediated Tissue Injury

Antibody-mediated inflammation

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives: Explain antibody-mediated inflammation

Identify the fixed-tissue targets of type II antibodies.

Trace complement activation to leukocyte-mediated injury.

Relate inflammatory effectors to tissue damage and clinical disease.

Distinguish tissue-bound antibody injury from immune-complex disease.

Antigen location

Complement products

Fc receptors

Clinicopathologic patterns

Slide 3 · Protective immune mechanisms can damage host tissue

Antibodies and leukocytes normally eliminate infectious agents.

The same effectors cause pathology if aimed at self or innocuous antigens.

Injury depends on antigen location, antibody action, and downstream cells.

Antibody specificity

Host-tissue recognition

Effector activation

Tissue injury

Slide 4 · Classification depends on the dominant effector mechanism

Hypersensitivity type

Principal injury mechanism

Type I — immediate

Th2/IgE, mast-cell mediators, late-phase leukocytes

Type II — antibody-mediated

IgG/IgM react with cell or fixed-tissue targets

Type III — immune complexes

Antigen–antibody complexes deposit and trigger inflammation

Type IV — T-cell-mediated

Cytokine-mediated inflammation or CTL cytotoxicity

Slide 5 · Type II hypersensitivity has three major outcomes

Antibodies recognize cell-surface or extracellular-matrix antigens.

Target and effector mechanism determine the clinical lesion.

Inflammation is one branch—not synonymous with all of type II injury.

Opsonization and cell removal

Complement/Fc-mediated inflammation

Receptor blockade or stimulation

Mechanisms may overlap

Slide 6 · Fixed-tissue antibodies initiate local inflammation

IgG binds antigens anchored to basement membranes or extracellular matrix.

Bound antibody can activate complement in situ.

Complement and antibody Fc regions recruit and activate inflammatory cells.

Fixed antigen

Antibody deposition

Complement + Fc engagement

Leukocyte-mediated injury

Slide 7 · Antigen location directs the site of tissue injury

Basement membrane is a major fixed-tissue target.

Extracellular matrix provides additional immobile antigens.

Antibody binding sites localize inflammation to structurally important compartments.

Glomerular basement membrane

Alveolar basement membrane

Vascular endothelium

Other extracellular matrix

Slide 8 · Type II differs from circulating immune-complex deposition

Both pathways can recruit complement and neutrophils.

The critical distinction is how antigen is presented at the injury site.

Type II antibodies bind fixed targets; Type III complexes form and deposit.

Type II

Type III

Antibody binds intrinsic tissue target

Target is structurally localized

Antigen–antibody complexes accumulate

Deposits may be circulating or formed in situ

Slide 9 · Autoantibody specificity determines tissue distribution

Antibodies react with specific host antigenic determinants.

Expression of the target in more than one organ can explain multi-organ disease.

Tissue damage remains localized to compartments bearing the target.

Specific epitope

Anatomic expression

Antibody binding

Organ-pattern injury

Slide 10 · IgG is the dominant antibody class in this mechanism

Type II diseases are commonly mediated by IgG.

IgG has Fc regions recognized by receptors on leukocytes.

IgG can activate the classical complement pathway in appropriate settings.

Fab recognizes antigen

Fc recruits effectors

Complement activation

Leukocyte engagement

Slide 11 · IgM can also initiate complement-dependent injury

Type II responses may involve IgG or IgM antibodies.

IgM bound to a suitable target efficiently engages classical complement activation.

Fc receptor–dependent leukocyte responses are most directly described for IgG.

Cell/tissue antigen

Target-bound IgM

Classical complement

Inflammatory effectors

Slide 12 · The inflammatory cascade follows a causal sequence

Antibody first binds a pre-existing antigenic target.

Complement activation produces chemotactic and permeability mediators.

Recruited leukocytes release damaging reactive molecules and enzymes.

IgG binds matrix

Complement fragments

Leukocyte recruitment

Oxidants + proteases

Slide 13 · Complement activation begins at the antibody-bound surface

Bound antibody activates complement by the classical pathway.

Effector products are generated near the antigen-bearing tissue.

Local production couples antigen recognition to inflammation.

Schematic — native PowerPoint shapes

Vascular / tissue matrix

Y

Y

Y

Y

Y

Y

Fixed antigen + bound IgG

Slide 14 · Complement cleavage produces distinct inflammatory signals

C3a and C5a increase vascular permeability as anaphylatoxins.

C5a is a major chemoattractant for granulocytes and monocytes.

C3b deposits on surfaces and is recognized by complement receptors.

C3a → permeability

C5a → chemotaxis

C3b → recognition

Inflammatory amplification

Slide 15 · C5a directs granulocytes toward antibody deposits

C5a is the major chemotactic agent highlighted in this pathway.

Granulocytes and monocytes migrate into affected tissue.

Recruitment precedes release of leukocyte-derived injurious substances.

Schematic — native PowerPoint shapes

Vascular / tissue matrix

Neutrophils migrate toward C5a

Slide 16 · C3a and C5a increase local vascular permeability

Anaphylatoxins modify the microvascular response.

Greater permeability facilitates inflammatory exudation.

Vascular change and chemotaxis cooperate to concentrate leukocytes.

Complement cleavage

C3a / C5a

Permeability rises

Inflammatory exudate

Slide 17 · Granulocytes and monocytes are key recruited effectors

Neutrophils are prominent acute inflammatory granulocytes.

Monocytes enter tissue and contribute macrophage functions.

Their tissue-destructive capacity requires local activation.

Neutrophil recruitment

Monocyte recruitment

Receptor engagement

Effector release

Slide 18 · Fc receptors couple bound IgG to leukocyte activation

Leukocytes recognize the Fc portions of tissue-bound IgG.

Engagement delivers an activation signal at the antibody-decorated site.

This recognition contributes directly to inflammatory tissue injury.

Tissue-bound IgG

Fc receptor engagement

Leukocyte activation

Enzymes + ROS

Slide 19 · Complement receptors cooperate with Fc receptors

Complement activation generates C3b on local surfaces.

Leukocyte complement receptors recognize bound complement fragments.

Engagement of Fc and complement receptors activates leukocyte effector functions.

IgG Fc region

C3b deposition

Leukocyte Fc receptor

Leukocyte C3b receptor

Slide 20 · Recognition and recruitment are distinct steps

Chemotactic products bring leukocytes to tissue.

Fc and complement receptors help activate recruited leukocytes.

Both are required to explain efficient localized inflammation.

Recruitment

Activation

C5a directs cell migration

Increased permeability supports entry

Fc receptors bind tissue IgG

Complement receptors detect C3b

Slide 21 · Activated leukocytes damage the extracellular matrix

Activated granulocytes and monocytes release lysosomal enzymes.

They generate reactive oxygen species (ROS).

Extracellular effector release damages tissue surrounding antibody deposits.

Schematic — native PowerPoint shapes

Vascular / tissue matrix

ROS + proteases disrupt matrix

Slide 22 · Proteases target basement membrane and connective tissue

Proteases can digest basement-membrane constituents.

Collagen and elastin are susceptible extracellular-matrix substrates.

Cartilage is also vulnerable to proteolytic injury.

Basement membrane

Collagen fibers

Elastin

Cartilage matrix

Slide 23 · Reactive oxygen species add a second mode of injury

Activated leukocytes generate oxidant species.

Oxidants can damage nearby cellular and extracellular structures.

Protease and oxidant injury may be concurrent.

Leukocyte activation

ROS generation

Oxidative tissue damage

Functional impairment

Slide 24 · The antigen need not be the structure ultimately destroyed

Antibody binding identifies a target site.

Released mediators can diffuse into neighboring tissue.

This explains inflammatory injury beyond the antigen-bearing molecule itself.

Schematic cross-section — not a histology image

Neutrophil recruitment

Fixed matrix antigen + antibody

Basement membrane / ECM

Slide 25 · Basement-membrane injury compromises tissue barriers

Basement membranes contribute to structural separation and filtration.

Leukocyte proteases can digest the matrix scaffold.

Barrier dysfunction leads to organ-specific clinical consequences.

Bound antibody

Leukocyte proteases

Matrix disruption

Barrier dysfunction

Slide 26 · The local lesion reflects location and inflammatory intensity

Capillary compartments are vulnerable when target antigens are accessible.

Leukocyte-rich inflammation can injure adjacent endothelium and matrix.

The resulting pathology varies with organ structure and severity.

Capillary endothelium

Subendothelial matrix

Leukocyte exudation

Parenchymal injury

Slide 27 · Anatomic context shapes the inflammatory phenotype

The same complement/Fc pathways operate in distinct organs.

Renal injury impairs the filtration barrier.

Pulmonary capillary injury may produce alveolar hemorrhage.

Glomerulus

Alveolus

Filtration barrier

Nephritic injury

Gas-exchange interface

Hemorrhage

Slide 28 · Acute tissue injury may be followed by remodeling

Continued or severe inflammation can extend tissue destruction.

Repair and chronic change may follow unresolved injury.

Clinical outcome depends on severity, duration and the organ involved.

Inflammatory insult

Matrix injury

Repair response

Residual dysfunction

Slide 29 · Glomeruli are a key example of fixed-target injury

Intrinsic glomerular basement membrane (GBM) antigens can bind autoantibodies.

The immune attack occurs along glomerular capillary walls.

Inflammation damages the filtration apparatus.

Schematic — native PowerPoint shapes

Vascular / tissue matrix

Y

Y

Y

Y

Y

Y

Fixed antigen + bound IgG

Slide 30 · Anti-GBM disease is a prototypical type II lesion

IgG reacts with an intrinsic component of the GBM.

Tissue-bound antibody drives inflammatory glomerular injury.

The deposition pattern follows the distribution of the fixed antigen.

Anti-GBM IgG

Linear GBM binding

Complement / leukocytes

Glomerulonephritis

Slide 31 · The anti-GBM target is shared by kidney and lung

The implicated autoantigen lies in the noncollagenous region of the α3 chain of type IV collagen.

This antigen is expressed in renal and pulmonary basement membranes.

Shared antigen localization accounts for the pulmonary–renal syndrome in some patients.

α3 chain of type IV collagen

Renal GBM

Alveolar basement membrane

Shared autoantibody

Slide 32 · Goodpasture syndrome links nephritis with pulmonary hemorrhage

Antibodies react with basement membranes of glomeruli and alveoli.

The kidneys develop inflammatory glomerular injury.

The lungs may develop hemorrhage due to alveolar basement membrane involvement.

Anti-basement membrane IgG

Renal + alveolar binding

Inflammatory injury

Nephritis + hemorrhage

Slide 33 · Linear GBM immunofluorescence reflects an intrinsic antigen

Intrinsic antigen is distributed along the entire GBM.

Bound IgG therefore outlines capillary walls continuously.

A linear immunofluorescence pattern supports anti-GBM antibody deposition.

Smooth continuous deposition

Slide 34 · Granular fluorescence reflects discrete immune deposits

Immune complexes accumulate as discrete deposits rather than continuous binding.

Their distribution produces a granular fluorescence pattern.

Discontinuous immune-complex deposits

Slide 35 · Anti-GBM and immune-complex GN have different origins

Antigen–antibody relationship

Characteristic tissue finding

Anti-GBM disease

IgG recognizes intrinsic GBM → typically linear deposition

Immune-complex GN

Preformed or in situ complexes → typically granular deposits

Shared downstream effectors

Complement / Fc-associated inflammatory injury

Diagnostic implication

Interpret deposits alongside morphology and clinical context

Slide 36 · Glomerular inflammation can disrupt filtration

Inflammation injures glomerular capillary walls.

Barrier dysfunction may allow blood components and protein into urine.

Severe injury can rapidly compromise glomerular filtration.

Capillary-wall injury

Filtration barrier defect

Hematuria / proteinuria

Reduced renal function

Slide 37 · Severe capillary damage may be accompanied by crescents

Crescent formation is an important response to severe glomerular injury.

Crescents primarily involve proliferating cells lining Bowman capsule.

Anti-GBM injury is one cause of rapidly progressive crescentic GN.

Glomerular capillary injury

Bowman-space response

Crescent formation

Rapidly progressive GN

Slide 38 · Pulmonary involvement reflects the same antigen specificity

Anti-basement-membrane antibodies can bind in the pulmonary alveolar wall.

Inflammatory injury can result in alveolar hemorrhage.

Absence of pulmonary hemorrhage does not exclude renal-limited anti-GBM disease.

Shared autoantigen

Alveolar antibody binding

Capillary-wall injury

Hemorrhage in some patients

Slide 39 · Clinical interpretation should integrate organ distribution

Pulmonary hemorrhage and glomerulonephritis suggest a pulmonary–renal process.

Anti-GBM disease is an important immune-mediated mechanism in this setting.

Other causes of pulmonary–renal syndromes exist and require differentiation.

Clinical presentation

Antibody testing

Renal biopsy pattern

Competing mechanisms

Slide 40 · Graft vasculature is another antibody-mediated target

Antibodies against donor alloantigens can bind graft endothelium.

Classical complement activation follows local antibody recognition.

Resultant vascular inflammation and endothelial injury impair graft function.

Donor-specific antibodies

Endothelial binding

Complement activation

Vascular injury

Slide 41 · Acute antibody-mediated rejection injures small vessels

Typical sites include glomeruli and peritubular capillaries in kidney grafts.

Inflammatory injury may be associated with complement-product deposition.

Small-vessel thrombosis may accompany the reaction.

Glomerulitis

Peritubular capillaritis

Complement-product deposition

Microvascular thrombosis

Slide 42 · C4d can indicate complement activation in graft injury

The classical complement pathway generates C4-derived products.

C4d deposition is described in the kidney-graft rejection context.

Interpretation requires graft morphology and appropriate clinical/serologic context.

Endothelial alloantibody

Classical complement

C4d deposition

Pathology correlation

Slide 43 · Antibody-mediated and cellular rejection are not identical

Grafts can be injured by both humoral and T-cell-mediated immunity.

Antibody-mediated rejection prominently affects microvasculature.

Cellular rejection includes tubulitis and lymphocyte-rich endotheliitis.

Antibody-mediated

T-cell-mediated

Endothelial alloantibody

Complement-associated capillary injury

Alloreactive lymphocytes

Tubulitis / endotheliitis

Slide 44 · Vascular injury can impair a transplanted organ

Endothelial damage alters microvascular integrity and flow.

Inflammation and thrombotic changes may coexist.

Reduced tissue perfusion contributes to graft dysfunction.

Vascular antibody binding

Endothelial inflammation

Flow impairment

Graft injury

Slide 45 · ANCA-associated vasculitis is mechanistically distinct

ANCA reacts with proteins associated with neutrophil granules.

This differs from antibody binding to a constitutive basement-membrane antigen.

Neutrophil activation is central to the inflammatory lesion.

Anti-GBM

ANCA vasculitis

Antibody binds fixed matrix

Linear deposition

Antibodies target neutrophil proteins

Pauci-immune glomerular pattern

Slide 46 · ANCA-related neutrophil activation can damage vessels

Antibodies recognize neutrophil granule-associated antigens.

Neutrophil activation and degranulation contribute to vascular inflammation.

ANCA vasculitis illustrates antibody-triggered inflammation without dense immunoglobulin deposits.

ANCA + neutrophil targets

Neutrophil activation

Degranulation

Vessel-wall injury

Slide 47 · Acute rheumatic fever illustrates antibody cross-reactivity

Antibody responses to streptococcal antigens can cross-react with host tissue.

Immune-mediated inflammation contributes to myocarditis and arthritis.

Cross-reactivity, not direct bacterial invasion, is central to the listed mechanism.

Streptococcal antigen

Cross-reactive antibody

Macrophage activation

Tissue inflammation

Slide 48 · Pemphigus is antibody injury by loss of adhesion

Autoantibodies target desmogleins in epidermal intercellular junctions.

Altered cell adhesion and proteolytic mechanisms contribute to skin blistering.

It is type II antibody-mediated injury, but not the same lesion as complement-driven GBM inflammation.

Antidesmoglein antibodies

Desmosomal dysfunction

Loss of keratinocyte cohesion

Intraepidermal blister

Slide 49 · Opsonization removes cells rather than injuring fixed matrix

In hemolytic anemia, antibody-coated red cells are removed by phagocytes.

In fixed-tissue inflammation, recruited leukocytes injure surrounding structures.

Both are type II, but their immediate tissue targets differ.

Opsonization

Inflammation

Mobile target: Blood cell

Phagocytosis / lysis

Fixed target: Tissue matrix

Extracellular proteases / ROS

Slide 50 · Autoimmune hemolytic anemia highlights the contrast

Antibodies bind red-cell membrane proteins.

Fc and complement recognition favors red-cell removal.

The principal manifestation is hemolysis and anemia—not localized matrix inflammation.

Anti-RBC antibodies

Red-cell opsonization

Phagocytosis

Anemia

Slide 51 · Antibodies may alter receptors without inflammation

Some type II antibodies impair or stimulate cell-surface receptor function.

Myasthenia gravis impairs neuromuscular transmission.

Graves disease stimulates the thyroid-stimulating hormone receptor.

Receptor blockade

Receptor stimulation

Altered physiology

May lack dominant inflammation

Slide 52 · Receptor dysfunction and tissue destruction must be separated

The clinical phenotype cannot be inferred from antibody presence alone.

An antibody that activates a receptor may produce hyperfunction.

An antibody that recruits complement to tissue can produce structural damage.

Functional disturbance

Inflammatory injury

Receptor blockade/stimulation

Altered cell signaling

Complement / Fc engagement

Matrix and cellular destruction

Slide 53 · Type III disease shares many terminal inflammatory mediators

Antigen and antibody form immune complexes in blood or tissues.

Deposited complexes activate complement and leukocytes.

The downstream inflammatory effectors overlap with type II inflammation.

Immune complexes

Tissue deposition

Complement + Fc effects

Inflammatory injury

Slide 54 · The initiating location separates types II and III

Dimension

Type II inflammation versus type III injury

Antigen distribution

II: Intrinsic / fixed; III: Complex-associated, circulating or in situ

Initial event

II: Antibody binding to tissue; III: Antigen–antibody complex formation/deposition

Downstream pathway

Both may activate complement and Fc receptors on leukocytes

Example

II: Anti-GBM disease; III: Immune-complex glomerulonephritis

Slide 55 · Complement consumption is context-dependent

Circulating immune-complex disease may consume complement systemically.

Decreased serum C3 during active serum sickness.

Do not assume every local antibody-mediated lesion causes low serum C3.

Systemic immune complexes

Fixed-tissue antibody

Complement consumption

C3 may decrease

Complement acts locally

Serum level varies by context

Slide 56 · Mechanistic pathology begins with the target site

Locate the antigen: Cell, receptor, matrix, or circulating complex.

Identify the effector: Phagocytosis, complement/Fc inflammation, or functional change.

Correlate the tissue pattern and organ manifestations.

Where is antigen?

Which antibody effect?

Which tissue response?

Which syndrome?

Slide 57 · Kidney biopsy information can resolve competing mechanisms

Light microscopy describes the structural injury pattern.

Immunofluorescence shows distribution of immunoglobulin/complement deposits.

Electron microscopy can demonstrate discrete electron-dense immune deposits.

Clinical and serologic data remain essential.

Light microscopy

Immunofluorescence

Electron microscopy

Clinicopathologic synthesis

Slide 58 · Linear and granular are patterns—not separate diagnoses

Linear staining strongly supports antibody binding to intrinsic GBM.

Granular staining suggests discrete immune-complex deposits.

Neither pattern should be interpreted without disease morphology and context.

Linear pattern

Granular pattern

Continuous GBM outline

Anti-GBM mechanism

Discrete deposits

Immune-complex mechanism

Slide 59 · Case application: Pulmonary hemorrhage with nephritic injury

A patient develops hemoptysis, hematuria, and rapidly deteriorating renal function. Which antibody-mediated mechanism could link the lung and kidney findings?

Consider autoantibody binding to a shared basement-membrane antigen.

Predict complement/Fc-driven inflammation at both sites.

Anticipate a linear GBM immunofluorescence pattern if anti-GBM disease is confirmed.

Slide 60 · Case resolution: Shared basement membrane explains both organs

A target within the α3 chain of type IV collagen occurs in kidney and lung.

IgG binds tissue-fixed antigen and activates inflammatory effectors.

Organ manifestations follow damage to glomerular and alveolar capillaries.

Shared target antigen

Renal + pulmonary IgG

Inflammatory capillary injury

Pulmonary–renal syndrome

Slide 61 · Case application: Early graft microvascular inflammation

A kidney transplant biopsy shows glomerulitis and peritubular capillaritis with complement-product deposition. Which humoral pathway should be considered?

Assess antibody-mediated rejection in the appropriate context.

Antibodies may target donor alloantigens on vascular endothelium.

Classical complement activation links antibodies to microvascular injury.

Slide 62 · Case resolution: Vascular antibody binding leads to graft damage

Alloantibody binding activates complement at graft endothelium.

The microvascular bed becomes inflamed and injured.

Focal thrombosis and organ dysfunction may accompany more severe injury.

Donor alloantigen

Endothelial antibody

Complement activation

Microvascular injury

Slide 63 · Case application: Necrotizing vasculitis with sparse deposits

Necrotizing vasculitis occurs with ANCA positivity but little immunoglobulin detected in renal tissue. Is dense tissue-bound IgG deposition required?

No: ANCA can activate neutrophils through a different antibody-associated process.

Neutrophil activation and degranulation drive vessel injury.

Contrast this mechanism with linear anti-GBM antibody deposition.

Slide 64 · Case application: Granular deposits in glomeruli

A glomerular sample has discrete granular immunoglobulin deposits. Does this pattern identify anti-GBM type II inflammation?

No: Granular deposition is characteristic of immune-complex-mediated mechanisms.

Both mechanisms can produce complement and leukocyte injury.

The source and arrangement of antigen–antibody interaction differ.

Slide 65 · Pitfalls when interpreting antibody-associated tissue injury

Common mistake

Correct interpretation

All IgG-mediated injury is inflammatory

Type II also includes opsonization and receptor dysfunction

All glomerular antibodies are immune complexes

Antibodies can bind intrinsic GBM in situ

Complement recruitment equals antigen specificity

Complement acts downstream of antigen–antibody recognition

ANCA vasculitis requires dense fixed deposits

ANCA-associated GN is typically pauci-immune

Slide 66 · Integrated pathway from antibody binding to organ dysfunction

Specific IgG attaches to fixed tissue components.

Complement fragments recruit cells and alter vascular permeability.

Fc/C3b-receptor engagement triggers enzyme and ROS release.

Matrix damage causes organ-dependent dysfunction.

Fixed tissue IgG

Complement products

Activated leukocytes

Structural injury

Slide 67 · Three questions summarize the pathologic mechanism

Where is the antigen: Tissue-fixed or within an immune complex?

Which effector dominates: Inflammatory cells, phagocytes, or receptor regulation?

What structural injury explains the clinical manifestation?

Target localization

Antibody binding

Inflammatory mediator

Clinical consequence

Slide 68 · Test your mechanism-based reasoning

Why does an antibody directed against a basement-membrane antigen produce inflammation instead of simple removal of the antigen?

The antigen is fixed in the tissue and cannot be engulfed like a circulating blood cell.

Complement activation and Fc receptor engagement recruit activated leukocytes.

Extracellular proteases and ROS injure the surrounding structural matrix.

Slide 69 · Selected textbook sources and figure contexts

Source section

Teaching material used

Chapter 6, pp. 181–182

Hypersensitivity definition and four-type classification

Chapter 6, pp. 185–188

Type II injury mechanisms, Fig. 6.16 and Table 6.3; type III contrast

Chapter 6, pp. 209–210

Acute antibody-mediated vascular graft rejection

Chapter 20, glomerular injury

Anti-GBM disease, linear/granular IF and crescentic GN