Granulomatous Inflammation

Slide 1 · GRANULOMATOUS

INFLAMMATION

Organized macrophage response to persistent stimuli

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Explain why a persistent or indigestible stimulus generates a granuloma.

Distinguish foreign-body and T-cell–dependent immune granulomas.

Identify the principal cellular and morphologic components.

Interpret key disease-associated patterns without equating pattern with cause.

Construct an etiology-directed workup for tissue granulomas.

Slide 3 · A granuloma is an organized macrophage collection

Macrophage core

Activated macrophages

Lymphocytic rim

Schematic — not a tissue image

Activated macrophages form the principal cellular component.

T lymphocytes often participate; Necrosis may or may not be present.

Organization reflects attempted containment of a difficult-to-clear stimulus.

Slide 4 · Granulomatous inflammation is a chronic pattern

Chronic inflammation

Prolonged response to persistent stimuli

Macrophages and lymphocytes predominate

Tissue injury and repair coexist

Granulomatous subset

Organized macrophage aggregates

Often a T-cell–macrophage circuit

Necrosis present in some lesions

Slide 5 · Persistent stimuli drive granuloma formation

Agent remains

Macrophages accumulate

Activation persists

Granuloma develops

The response is sustained because the stimulus is not readily eliminated.

Organization may sequester the agent but does not guarantee eradication.

Slide 6 · Containment and collateral injury coexist

Potential benefit

Limits dispersion of resistant material

Concentrates phagocytes around the stimulus

Supports sustained local host defense

Potential cost

Activated cells injure adjacent tissue

Necrosis may accompany the reaction

Repair may culminate in scarring

Slide 7 · Chronic inflammation contains injury and repair

Activated

Macrophages

Mediator release

Tissue

Injury

Local damage

Fibroblast

Response

Repair / fibrosis

Inflammatory mediators sustain leukocyte recruitment.

Activated macrophages can damage parenchymal tissue.

The same cells contribute to fibroblast activation and repair.

Slide 8 · Macrophages arise from several sources

Blood monocyte

Tissue migration

Macrophage

Activation

Many macrophages in inflamed tissue arise from marrow-derived monocytes.

Some organs also contain long-lived tissue-resident macrophages.

Slide 9 · Resident and recruited macrophages

Recruited population

Monocytes enter inflamed tissues

Continued influx maintains chronic infiltrates

May become dominant within ~48 hours

Tissue-resident population

Established early in some organs

Examples: Microglia, Kupffer cells

Contribute to local immune responses

Slide 10 · Macrophages link defense, signaling and repair

Phagocytose

Release mediators

Interact with T cells

Promote repair

The same functional repertoire can both protect and injure tissue.

Their persistence is central to chronic inflammation.

Slide 11 · Macrophage–T-cell communication is reciprocal

Antigen-presenting

Macrophage

Activated

CD4 T cell

Antigen

Presentation

IFN-γ

Macrophages present antigens and influence T-cell responses.

Activated T cells release cytokines that modify macrophage function.

The feedback loop can maintain an inflammatory lesion.

Slide 12 · Classical activation favors inflammatory defense

Microbial products / IFN-γ

Macrophage activation

NO, ROS, enzymes

Microbial killing

Classical or M1-like activation can intensify inflammation and tissue injury.

Slide 13 · Alternative activation supports tissue repair

IL-4 / IL-13

Macrophage activation

Repair-promoting activity

Inflammation resolution

This is a functional polarization concept—not proof of a homogeneous cell subset.

Slide 14 · M1-like and M2-like labels have limitations

Useful model

Different signals elicit different functions

Classical: Killing and inflammation

Alternative: Resolution and repair

Biologic reality

Phenotypes overlap and change

Mixed states occur in lesions

Strict M1 → M2 temporal sequence is unproven

Slide 15 · Two mechanistic categories of granuloma

Dimension

Foreign-body

Immune

Trigger

Inert, indigestible material

Persistent antigen or microbe

T-cell dependence

No specific T-cell response required

T-cell–mediated response central

Major components

Macrophages and giant cells

Activated macrophages and T cells

Primary clue

Material in/near center

Persistent immunologic stimulus

Slide 16 · Foreign-body granulomas form without specific immunity

Foreign material

Activated macrophages

Lymphocytic rim

Schematic — not a tissue image

Inert foreign substances are large or otherwise difficult to ingest.

Macrophages and giant cells gather along the foreign surface.

A specific T-cell–mediated immune response is not required.

Slide 17 · Failure of phagocytosis localizes the reaction

Large inert material

Phagocytosis impeded

Surface-apposed macrophages

Giant cells accumulate

The physical properties of the foreign material help determine the lesion’s architecture.

Slide 18 · Recognized foreign-body triggers

Suture material left in tissue after a procedure.

Talc particles; Exposure can occur with intravenous drug use.

Other fibers or inert materials too large for ordinary phagocytosis.

These examples are nonimmunogenic description.

Slide 19 · Foreign-body reaction: Cellular disposition

Foreign material

Activated macrophages

Lymphocytic rim

Schematic — not a tissue image

Cells gather along the foreign-material interface.

Multinucleated giant cells may directly abut or contain material.

Identifying the foreign object changes the etiologic interpretation.

Slide 20 · Polarized microscopy can reveal foreign material

Inspect H&E

Look for central material

Use polarized light

Assess refractility

Not all foreign substances are equally refractile.

Polarization is an adjunct to, not a replacement for, routine morphology.

Slide 21 · Reasoning from a possible foreign-body granuloma

Localize the cellular aggregate

Search for recognizable central material

Examine with polarized light

Correlate with exposure or procedure

The morphologic pattern suggests, but does not independently prove, the source.

Slide 22 · Immune granulomas depend on sustained T-cell responses

Macrophage core

Activated macrophages

Lymphocytic rim

Schematic — not a tissue image

Persistent microbes and other stimuli activate T cells.

T-cell cytokines sustain macrophage activation.

The resulting focus may damage local tissue despite its containment function.

Slide 23 · Adaptive immunity maintains an immune granuloma

Persistent stimulus

T-cell activation

Cytokine signaling

Activated macrophages

The stimulus must remain sufficiently persistent to sustain the cellular response.

Slide 24 · Th1 cells activate macrophages through IFN-γ

Antigen-driven Th1 response

IFN-γ release

Macrophage activation

Granuloma maintenance

IFN-γ is a central mechanistic link emphasized.

Slide 25 · Th1–macrophage signaling forms a reinforcing loop

Antigen-presenting

Macrophage

Activated

CD4 T cell

Antigen

Presentation

IFN-γ

T cells release IFN-γ that increases macrophage activation.

Macrophages present antigen and sustain T-cell interactions.

Amplification is helpful against microbes but can damage host tissue.

Slide 26 · T-cell subsets shape the inflammatory milieu

Subset

Textbook mediators

Principal effect

Th1

IFN-γ

Classical macrophage activation

Th2

IL-4, IL-5, IL-13

Eosinophils; Alternative activation

Th17

IL-17

Chemokines; Neutrophil / monocyte recruitment

Slide 27 · Schistosomiasis illustrates a Th2-associated pattern

Parasitic stimulus

Strong Th2 response

Eosinophil recruitment

Granulomatous inflammation

Schistosomiasis as a granulomatous setting with a prominent Th2/eosinophilic response.

Slide 28 · Foreign-body versus immune granuloma: Practical clues

Question

Foreign-body pattern

Immune pattern

What is in the lesion?

Visible/refractile material possible

Specific stimulus may be microscopic

What sustains the cells?

Persistent inert surface

Persistent T-cell activation

Which pathway dominates?

Macrophage/giant-cell response

T-cell–macrophage interaction

What confirms the cause?

Material and exposure correlation

Organism / disease-specific studies

Slide 29 · Epithelioid cells are activated macrophages

Epithelioid cell

Activated macrophages

Lymphocytic rim

Schematic — not a tissue image

Macrophages enlarge and develop abundant cytoplasm.

Their epithelial-like appearance explains the name “epithelioid.”

They are not derived from epithelial cells.

Slide 30 · Multinucleated giant cells arise by fusion

Fused giant cell

Activated macrophages

Lymphocytic rim

Schematic — not a tissue image

Some activated macrophages fuse to form giant cells.

A giant cell contains multiple nuclei within one cytoplasm.

Giant cells can occur in both granuloma types.

Slide 31 · Granulomas have recognizable spatial organization

Macrophage core

Activated macrophages

Lymphocytic rim

Schematic — not a tissue image

An activated macrophage aggregate forms the principal focus.

T lymphocytes often surround or intermingle with it.

Some lesions have peripheral fibroblasts and connective tissue.

Slide 32 · Necrosis may be absent or present

Nonnecrotizing pattern

Organized epithelioid cell aggregate

No central necrotic zone identified

Described in sarcoidosis and Crohn disease

Necrotizing pattern

Central necrotic material present

Common prototype: Tuberculosis

Necrosis alone does not identify an organism

Slide 33 · Caseating granulomas include central necrosis

Necrotic center

Activated macrophages

Lymphocytic rim

Schematic — not a tissue image

A necrotic center contains amorphous granular debris.

The center is surrounded by activated macrophages.

Lymphocytes and fibroblasts may form a more peripheral rim.

Slide 34 · Chronic granulomas may acquire fibrous rims

Sustained inflammation

Macrophage mediators

Fibroblast response

Scar formation

Repair can coexist with persistent inflammation and tissue injury.

Slide 35 · Necrotizing granuloma: Schematic cross-section

Necrotic center

Activated macrophages

Lymphocytic rim

Schematic — not a tissue image

Central necrosis is a distinct compartment.

Epithelioid cells and giant cells occupy the cellular zone.

A surrounding lymphocytic/fibroblast-rich region may be present.

Slide 36 · Nonnecrotizing granuloma: Schematic cross-section

Macrophage core

Activated macrophages

Lymphocytic rim

Schematic — not a tissue image

Activated macrophages occupy the core.

T lymphocytes can surround and intermingle with macrophages.

Absence of necrosis does not identify a unique etiology.

Slide 37 · Reading granulomatous histology systematically

Recognize macrophage aggregate

Assess epithelioid and giant cells

Record necrosis or suppuration

Search for foreign material / organisms

Describe what is actually present before inferring a cause.

Slide 38 · Morphology suggests an etiology, not a final answer

What morphology can do

Define the reaction pattern

Prioritize plausible causes

Guide targeted ancillary tests

What morphology cannot do alone

Identify every organism

Exclude infection reliably

Replace clinical and microbiologic data

Slide 39 · Tuberculosis: Prototype infectious granuloma

Tuberculosis

Mycobacterium tuberculosis

ETIOLOGY

Often caseating “tubercles”; Epithelioid histiocytes, giant cells, lymphocytes and a necrotic center

PATTERN / TISSUE REACTION

Always evaluate for tuberculosis when granulomas are discovered.

Slide 40 · The classic tubercle has layered components

Necrotic center

Activated macrophages

Lymphocytic rim

Schematic — not a tissue image

Amorphous granular necrosis occupies the center.

Epithelioid macrophages and occasional Langhans giant cells are present.

Lymphocytes and fibroblasts surround the focus.

Slide 41 · Tuberculosis requires microbiologic confirmation

Granulomatous morphology

Acid-fast stain

Culture or molecular test

Etiologic diagnosis

A characteristic granuloma is a clue; Organism identification is the objective.

Slide 42 · Tuberculosis can overlap with other patterns

Supports tuberculosis

Caseating epithelioid granulomas

Compatible host and clinical setting

Demonstration of acid-fast bacilli

Does not prove tuberculosis

Necrosis without microbial evidence

A giant cell by itself

A nonnecrotizing pattern alone

Slide 43 · Leprosy: Macrophages can harbor acid-fast bacilli

Leprosy

Mycobacterium leprae

ETIOLOGY

Acid-fast bacilli within macrophages; Noncaseating granulomas comparison

PATTERN / TISSUE REACTION

Interpret with the complete tissue findings and organism-directed study.

Slide 44 · Syphilis: The granulomatous gumma

Syphilis

Treponema pallidum

ETIOLOGY

Gumma surrounded by histiocytes; Plasma-cell infiltrate; Central necrotic cells may retain their outlines

PATTERN / TISSUE REACTION

Serologic studies are an important component of etiologic evaluation.

Slide 45 · Cat-scratch disease: Granulomas with neutrophils

Cat-scratch disease

Bartonella henselae

ETIOLOGY

Rounded or stellate granuloma; Granular central debris and recognizable neutrophils

PATTERN / TISSUE REACTION

Giant cells are uncommon in this pattern.

Slide 46 · Sarcoidosis: A noncaseating example

Sarcoidosis

Unknown etiology

ETIOLOGY

Noncaseating granulomas with abundant activated macrophages

PATTERN / TISSUE REACTION

Noncaseating architecture does not eliminate infectious possibilities.

Slide 47 · Crohn disease: Granulomas in the intestinal wall

Crohn disease

Immune response to intestinal bacteria; Possible self-antigens

ETIOLOGY

Occasional noncaseating granulomas with dense chronic inflammation in the intestinal wall

PATTERN / TISSUE REACTION

A granuloma must be interpreted with bowel distribution and other pathology.

Slide 48 · Etiologic classification: Examples

Category

Examples

Common reaction feature

Infectious

Tuberculosis; Leprosy

Mycobacterial / acid-fast association

Infectious

Syphilis; Cat-scratch disease

Gumma or suppurative granuloma

Immune-mediated / unknown

Crohn disease; Sarcoidosis

Often noncaseating pattern

Foreign material

Suture; Talc; Fibers

Particle-centered giant-cell response

Slide 49 · Compare textbook granulomatous disease patterns

Disease

Distinctive clue

Caution

Tuberculosis

Caseating tubercle

Confirm M. Tuberculosis

Syphilis

Gumma; Plasma cells

Use etiology-specific testing

Cat-scratch

Stellate / neutrophilic center

Suppuration is a clue

Sarcoidosis

Noncaseating focus

Exclude mimics

Crohn disease

Occasional intestinal granulomas

Requires tissue/context integration

Slide 50 · Location and clinical context refine the differential

Intestinal wall with chronic mucosal disease: Crohn disease may enter the differential.

Granulomatous lymphadenitis with neutrophils: Consider a suppurative cause.

Implant or suture site: Search directly for embedded material.

Any granulomatous lesion demands evaluation for infectious causes, particularly tuberculosis.

Slide 51 · Necrosis does not uniquely diagnose tuberculosis

What necrosis tells you

Tissue destruction occurred

A necrotizing granuloma is present

Tuberculosis becomes important to test

What it cannot tell you

Which organism is responsible

Whether organisms remain viable

Whether all infection has been excluded

Slide 52 · Nonnecrotizing does not uniquely diagnose sarcoidosis

Examples with nonnecrotizing lesions

Sarcoidosis

Crohn disease

Leprosy in textbook table

What to do next

Review organ site and systemic history

Assess organism-specific evidence

Correlate with other tissue features

Slide 53 · Initial questions after identifying a granuloma

Does it contain identifiable foreign material?

Is there necrosis or suppuration?

Where is the lesion and what is the clinical setting?

Which organisms or diseases need specific tests?

Slide 54 · Polarized light is an adjunct for foreign material

Routine microscopy

Identify suspicious particles

Polarized illumination

Refractility assessment

Some foreign material can be found within giant cells.

A negative polarized-light finding does not by itself resolve etiology.

Slide 55 · Special stains target suspected organisms

Granuloma recognized

Select organism stain

Examine for organisms

Interpret with morphology

The textbook specifically cites acid-fast staining for tubercle bacilli.

Slide 56 · Culture provides organism-directed confirmation

Suspect infection

Obtain suitable material

Culture for microbe

Interpret result

Culture methods for tuberculosis and fungal diseases.

Culture requires appropriately collected clinical material.

Slide 57 · Molecular testing may establish an infectious cause

Morphologic suspicion

Select targeted PCR

Microbial sequence detected

Integrate evidence

The chapter specifically mentions polymerase chain reaction in tuberculosis.

Slide 58 · Serology can answer selected etiologic questions

Compatible morphology

Relevant clinical question

Targeted serologic test

Integrated interpretation

The chapter highlights serologic studies for syphilis.

Slide 59 · Integrated diagnostic workflow

Describe the granulomatous pattern

Evaluate foreign material and tissue context

Exclude key infections using appropriate studies

Integrate ancillary findings with clinical evidence

No single morphologic pattern can substitute for identifying the cause.

Slide 60 · Case: Nodule at a previous operative site

Clinical–pathologic observation

A localized nodule develops at the site of an earlier surgical repair. Biopsy contains histiocytes and multinucleated giant cells surrounding a small linear structure.

Which etiologic class is favored, and which microscope technique could help?

Look for material at the center.

Slide 61 · Case resolution: Foreign-body granuloma

Suture-associated material

Macrophage/giant-cell reaction

Foreign-body granuloma

Polarization as adjunct

Local exposure and material identify the likely trigger.

This mechanism does not require an antigen-specific T-cell response.

Slide 62 · Case: Necrotizing granulomatous lymphadenitis

Clinical–pathologic observation

A lymph node contains an epithelioid granuloma with central amorphous necrotic debris and a peripheral lymphocytic rim. No organism is identified on routine H&E.

Which infectious disease must be excluded, and which confirmatory tests are named?

Morphology alone is insufficient.

Slide 63 · Case resolution: Exclude tuberculosis

Caseating granuloma

Test for acid-fast bacilli

Culture / PCR as indicated

Integrate organism evidence

Necrosis increases concern but does not establish mycobacterial etiology.

Slide 64 · Case: A nonnecrotizing intestinal granuloma

Clinical–pathologic observation

An intestinal wall biopsy shows a small nonnecrotizing epithelioid granuloma together with a chronic inflammatory infiltrate.

Which immune-mediated disease fits, and what diagnostic shortcut is unsafe?

Granuloma pattern is not disease-specific.

Slide 65 · Case resolution: Clinicopathologic correlation

Intestinal site

Nonnecrotizing granuloma

Crohn disease considered

Exclude plausible mimics

The histologic pattern fits but cannot alone establish the full diagnosis.

Slide 66 · Common reasoning errors and the corrective step

Error

Why misleading

Corrective action

“Caseation proves TB”

Pattern overlaps other causes

Pursue organism-specific studies

“No necrosis proves sarcoidosis”

Several diseases are nonnecrotizing

Correlate site and etiologies

“Giant cells prove infection”

Foreign-body reactions also form them

Look for particles / exposure

“H&E identifies every cause”

Organisms/material may be subtle

Use ancillary tests

Slide 67 · Integrated mechanism–morphology comparison

Origin

Dominant driver

Clue to investigate

Foreign material

Inert, hard-to-ingest particle

Embedded/refractile material

Mycobacterial infection

Persistent microbial antigen

Tubercle; Targeted microbiology

Th2-related parasite

Parasite-driven response

Eosinophil-rich granuloma

Crohn / sarcoidosis

Immune context / uncertain cause

Organ site and exclusion of infection

Slide 68 · Synthesis: Four rules for tissue granulomas

Granuloma = organized collection of activated macrophages, often with T cells.

Foreign-body and immune granulomas differ primarily in their initiating mechanism.

Epithelioid cells, giant cells, necrosis and fibrosis are components—not etiologic proof.

Confirm the cause by combining morphology, exposure, clinical context and targeted tests.

Slide 69 · Primary reference and scope

Robbins, Cotran & Kumar: Pathologic Basis of Disease. 11th edition (2026).

Chapter 3, “Inflammation and Repair,” granulomatous inflammation (pp. 90–91).

Parent sections: chronic inflammation, macrophages and lymphocytes (pp. 87–90).

Disease examples and microscopic descriptions follow Table 3.9.

All diagrams in this lecture are original, editable teaching schematics—not photomicrographs.