Tissues of the Immune System

Slide 1 · Tissues of the Immune System

Anatomical organization of adaptive immunity

Primary organs

Lymphocyte development

Secondary organs

Antigen-driven responses

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Distinguish primary from secondary lymphoid organs by developmental and immune functions.

Trace antigen delivery to lymph nodes, spleen and barrier-associated lymphoid tissues.

Identify T-cell and B-cell compartments in lymph nodes and splenic white pulp.

Explain how dendritic cells, follicular dendritic cells and macrophages support immunity.

Contrast trafficking of naive lymphocytes, effector T cells and antibody-secreting plasma cells.

Slide 3 · Immune tissues are organized by function

Primary (central) organs generate immunocompetent lymphocytes.

Secondary (peripheral) organs initiate adaptive responses to microbes.

Anatomical specialization links maturation, antigen capture and effector action.

Primary organs

Thymus

Bone marrow

Secondary organs

Lymph nodes

Spleen

Mucosal / cutaneous tissues

Organ classification · schematic

Slide 4 · Primary and secondary organs form a functional network

Lymphocytes develop in generative sites before entering peripheral immune surveillance.

Antigen is concentrated at secondary sites where circulating lymphocytes search.

Activated effectors subsequently function beyond the site of initiation.

Maturation

Secondary-organ encounter

Adaptive response

Effector function

Functional sequence · schematic

Slide 5 · Primary organs prepare cells for antigen recognition

Their defining task is lymphocyte development and acquisition of responsiveness.

T- and B-cell maturation occurs at anatomically distinct sites.

This stage is different from initiation of a response to a peripheral microbe.

Generative

Cells mature and become competent

Peripheral

Antigen-driven responses begin

Slide 6 · The thymus is the site of T-cell development

The thymus is a primary lymphoid organ.

T lymphocytes mature here before participating in peripheral adaptive responses.

This developmental role distinguishes thymus from lymph-node T-cell zones.

Thymus

Developing T lymphocyte

Mature T lymphocyte

Functional sequence · schematic

Slide 7 · Bone marrow is a central lymphocyte-generative site

Bone marrow produces blood cells, including naive B lymphocytes.

It is the primary organ emphasized for B-cell generation.

Later, plasma cells may reside in marrow while secreting antibodies.

Bone marrow

Naive B lymphocyte

Peripheral B-cell follicle

Functional sequence · schematic

Slide 8 · T- and B-cell developmental sites differ

T lineage: Thymic development is the central-organ role.

B lineage: Bone marrow generates naive B cells.

Both lineages subsequently participate in peripheral adaptive immunity.

T lineage

Thymus

T-cell zones

B lineage

Bone marrow

B-cell follicles

Parallel pathways · schematic

Slide 9 · Maturation and activation are distinct events

Maturation yields lymphocytes capable of responding to antigen.

Initiation occurs when antigen is presented or encountered in secondary organs.

Effector-cell migration is a subsequent, functionally separate phase.

Maturation

Antigen encounter

Activation

Response

Functional sequence · schematic

Slide 10 · Secondary organs are sites of adaptive immune initiation

Major sites are lymph nodes, spleen and lymphoid tissues associated with barriers.

Their architecture concentrates antigens and circulating naive lymphocytes.

Spatial organization helps coordinate cellular and humoral arms.

Secondary tissues

Lymph nodes: Lymph

Spleen: Blood

Skin / mucosa: Barrier entry

Organ classification · schematic

Slide 11 · Three architectural advantages promote immunity

Antigens are delivered to, trapped in or carried into these organs.

Naive lymphocytes circulate through the same sites searching for antigen.

T and B cells occupy organized neighborhoods that enable coordination.

Concentrate antigen

Recruit surveying cells

Organize interactions

Immune

Function

Conceptual relationship · schematic

Slide 12 · Antigen capture increases local encounter opportunity

Without concentration, antigen and rare responsive lymphocytes may remain separated.

Secondary-organ filtering brings antigens and adaptive immune cells together.

The delivery route determines whether a node, spleen or barrier tissue is engaged.

Distributed antigen

Concentration at lymphoid site

Cellular recognition

Functional sequence · schematic

Slide 13 · Naive lymphocytes survey secondary lymphoid tissue

Naive lymphocytes travel between blood and peripheral lymphoid organs.

Their repeated passage allows searching where microbial antigens accumulate.

This trafficking is particularly important for naive T cells.

Circulation

Secondary-organ survey

Antigen found?

Response initiated

Functional sequence · schematic

Slide 14 · T- and B-cell zoning partitions immune work

T lymphocytes localize preferentially to dedicated T-cell compartments.

B lymphocytes concentrate in follicular areas.

Different antigen-presenting cells are associated with these neighborhoods.

T-cell zone

Dendritic cells

T-cell activation

B-cell zone

Follicular dendritic cells

B-cell response

Parallel pathways · schematic

Slide 15 · Antigen entry route predicts the responding organ

Tissue or epithelial antigens may move in lymph to draining lymph nodes.

Blood-borne antigens are monitored by the spleen.

Barrier-associated lymphoid tissue responds at mucosal and cutaneous surfaces.

Tissue or epithelium

Draining lymph node

Bloodstream

Spleen

Barrier entry

Mucosal / cutaneous system

Organ classification · schematic

Slide 16 · Lymph nodes sample antigens from tissue drainage

Nodes are nodular aggregates located along lymphatic channels.

Lymph flows slowly through nodes, allowing antigen surveillance.

APCs in nodes can recognize antigen brought from peripheral tissues.

Tissue antigen

Lymphatic channel

Lymph node

Immune surveillance

Functional sequence · schematic

Slide 17 · Their position along lymphatics is functional

Foreign material reaching tissue spaces can enter lymphatic drainage.

A node intercepts the lymph traversing that drainage territory.

This arrangement explains why the draining node receives localized tissue antigens.

Epithelial breach

Local tissue

Afferent lymph

Draining node

Functional sequence · schematic

Slide 18 · Dendritic cells transport sampled antigens to nodes

Dendritic cells are located below epithelia and in tissue interstitium.

They capture microbial material and travel by lymphatics to lymph nodes.

They enter T-cell zones where naive T cells can recognize presented peptides.

Peripheral DC captures antigen

DC migrates in lymph

Node T-cell zone

Naive T cell encounters DC

Functional sequence · schematic

Slide 19 · Antigens can also arrive directly in lymph

Microbial antigens entering tissues may be transported in lymph.

APCs within nodes are positioned to recognize these incoming materials.

This complements transport by antigen-bearing dendritic cells.

Soluble or particulate antigen

Lymphatic fluid

Node APC

Antigen-bearing cell

Migrating dendritic cell

Node T-cell zone

Parallel pathways · schematic

Slide 20 · A draining lymph node concentrates tissue antigen

Antigens from microbes entering epithelia or local tissues converge via drainage.

Lymphatic delivery makes antigen available within the node.

Because many foreign antigens enter through tissues, nodes initiate many responses.

Local microbial entry

Antigen in tissue / DC

Drainage territory

Responding lymph node

Functional sequence · schematic

Slide 21 · Conventional dendritic cells initiate T-cell responses

Dendritic cells are major antigen-presenting cells for naive T cells.

They express high levels of MHC and molecules needed for T-cell activation.

Their location in T-cell zones aligns the APC with its principal target.

Capture

DC below epithelium

Microbial antigen

Presentation

DC in T-cell zone

Naive T lymphocyte

Parallel pathways · schematic

Slide 22 · The lymph-node cortex contains B-cell follicles

Follicles lie around the peripheral cortex of a lymph node.

They are sites of concentrated B lymphocytes.

Follicular dendritic cells support antigen recognition within follicles.

Cortical B-cell

Follicles

Paracortex

(T-cell region)

Medulla

Simplified lymph-node compartment schematic—not an H&E section

Slide 23 · Follicles are organized B-cell compartments

The follicle is an anatomical lymphocyte neighborhood rather than a random cluster.

B cells localize near FDCs that retain antibody- or complement-bound antigen.

Such proximity supports development of humoral immune responses.

B cell

Recognizes antigen within follicular milieu

FDC

Traps antigen complexes for B cells

Slide 24 · Recent B-cell activation can produce germinal centers

A follicle that has recently responded to antigen may develop a germinal center.

The germinal center occupies the central part of that responding follicle.

Its presence indicates an antigen-responsive follicular compartment in this source.

Follicle

Responding follicle

Germinal center

Antigen response may produce a central germinal center

Simplified follicular schematic; Not a histology image

Slide 25 · The paracortex contains concentrated T lymphocytes

The T-cell-rich paracortex lies next to the cortical follicles.

Conventional dendritic cells reside in this compartment.

The arrangement enables antigen presentation to T lymphocytes.

Cortical B-cell

Follicles

Paracortex

(T-cell region)

Medulla

Simplified lymph-node compartment schematic—not an H&E section

Slide 26 · Antigen-presenting cells are compartment-specific

Conventional dendritic cells present antigen to T cells in the paracortex.

Follicular dendritic cells display trapped antigen to B cells in follicles.

The two dendritic populations differ in lineage and immunologic function.

Feature

Conventional DC

Follicular DC

Usual zone

Paracortex

Follicle / germinal center

Principal interaction

Naive T cell

B cell

Source role

T-cell priming

Humoral response

Slide 27 · Cortex, paracortex and medulla provide orientation

Cortical follicles and adjacent paracortex are different lymphocyte compartments.

The medulla lies deeper within the lymph node.

A schematic cross-section can orient these regions but is not histologic evidence.

Cortical B-cell

Follicles

Paracortex

(T-cell region)

Medulla

Simplified lymph-node compartment schematic—not an H&E section

Slide 28 · Lymph-node zoning links structure with function

Antigen travels into a node from peripheral tissue.

T cells scan presented antigen in the paracortex.

B cells occupy follicles and may form germinal centers after responding.

Cortical B-cell

Follicles

Paracortex

(T-cell region)

Medulla

Simplified lymph-node compartment schematic—not an H&E section

Slide 29 · A node integrates two principal antigen-delivery modes

Lymph transports antigen from peripheral sites.

Migrating dendritic cells carry acquired antigens from tissues.

The node combines antigen delivery with organized T/B lymphocyte populations.

Fluid pathway

Antigen in lymph

APCs in node

Cellular pathway

Tissue dendritic cell

T-zone presentation

Parallel pathways · schematic

Slide 30 · The spleen monitors the blood rather than lymph

Blood-borne microbial antigens are intercepted in the spleen.

The organ is a functional counterpart to nodes for blood-derived antigen.

Its macrophage- and DC-associated sinusoids contribute to antigen trapping.

Bloodstream antigen

Splenic blood channels

APC capture

Adaptive response

Functional sequence · schematic

Slide 31 · Sinusoids expose incoming blood to immune cells

Blood entering the spleen passes through a network of sinusoids.

Macrophages and dendritic cells line these channels in the source description.

They trap blood-borne microbial antigens for initiation of adaptive immunity.

Arteriole

PALS

(T cells)

White-pulp

B-cell follicle

Blood sinusoids /

Red-pulp region

Highly simplified spleen white-pulp schematic; Not tissue morphology

Slide 32 · Macrophages and DCs cooperate in splenic surveillance

Both cell populations contribute to capture of blood-borne antigens.

Dendritic cells link capture to T-cell activation.

Macrophages also perform antigen presentation and microbial disposal.

Dendritic cell

Antigen capture and T-cell presentation

Macrophage

Antigen capture, presentation and ingestion

Slide 33 · Splenic white pulp organizes lymphocytes

T lymphocytes collect in periarteriolar lymphoid sheaths.

B lymphocytes inhabit white-pulp follicles.

These are specialized zones for responses to antigens delivered by blood.

Arteriole

PALS

(T cells)

White-pulp

B-cell follicle

Blood sinusoids /

Red-pulp region

Highly simplified spleen white-pulp schematic; Not tissue morphology

Slide 34 · Periarteriolar lymphoid sheaths are T-cell zones

T cells surround small arterioles in a sheath-like distribution.

The distribution gives this white-pulp component its name: PALS.

It parallels the T-cell-rich paracortex of a lymph node.

Arteriole

PALS

(T cells)

White-pulp

B-cell follicle

Blood sinusoids /

Red-pulp region

Highly simplified spleen white-pulp schematic; Not tissue morphology

Slide 35 · Splenic follicles contain the B-cell compartment

Splenic B cells reside in follicles analogous to nodal follicles.

Follicles form part of splenic white pulp.

Their separation from PALS maintains a spatial B/T division.

Arteriole

PALS

(T cells)

White-pulp

B-cell follicle

Blood sinusoids /

Red-pulp region

Highly simplified spleen white-pulp schematic; Not tissue morphology

Slide 36 · Splenic T- and B-cell areas are complementary

Antigen capture in splenic blood channels occurs near immune-cell-rich tissue.

PALS position T cells around arterioles.

Follicles position B cells for humoral responses.

PALS

Arteriole-associated

T lymphocytes

Follicle

White-pulp B-cell area

B lymphocytes

Parallel pathways · schematic

Slide 37 · Nodes and spleen differ primarily in what they sample

Nodes: Antigens entering lymphatics from peripheral tissues.

Spleen: Antigens circulating through the bloodstream.

Both concentrate antigen and organize T/B lymphocytes.

Comparison

Lymph node

Spleen

Incoming antigen

Tissue / lymph

Blood

T-cell location

Paracortex

PALS

B-cell location

Cortical follicle

White-pulp follicle

Slide 38 · The same microbial antigen may follow distinct routes

An antigen localized in tissue is commonly carried through lymphatic drainage.

A blood-circulating antigen is sampled by the spleen.

Organ selection follows the antigen’s anatomical distribution, not a fixed microbial label.

Peripheral tissue

Lymphatic drainage

Lymph node

Circulating blood

Splenic filtration

Spleen

Parallel pathways · schematic

Slide 39 · Mucosal and cutaneous systems guard barriers

Lymphoid tissue lies beneath epithelial surfaces of skin and mucosa.

Gut and respiratory mucosa are major mucosal immune locations.

These systems respond to antigens that cross breaches in epithelia.

Mucosal epithelium

External antigen

Subepithelial lymphoid cells / antigen-presenting cells

Entry across epithelium → local antigen sampling and response

Barrier-associated immune tissue · schematic

Slide 40 · The epithelial barrier determines initial antigen access

Intact epithelial surfaces physically separate external materials from immune tissue.

When antigen crosses the barrier, underlying immune cells can respond.

This spatial arrangement applies to cutaneous as well as mucosal sites.

Mucosal epithelium

External antigen

Subepithelial lymphoid cells / antigen-presenting cells

Entry across epithelium → local antigen sampling and response

Barrier-associated immune tissue · schematic

Slide 41 · Respiratory and gastrointestinal mucosa are immune sites

Both tracts expose large epithelial surfaces to environmental material.

Lymphoid cells associated with their mucosa can respond to entering antigens.

The anatomical association distinguishes mucosal tissue from spleen and nodes.

Airway mucosa

Surface exposure

Mucosal lymphocytes

Intestinal mucosa

Surface exposure

Mucosal lymphocytes

Parallel pathways · schematic

Slide 42 · Pharyngeal tonsils are organized mucosal tissue

Pharyngeal tonsils are anatomically defined components of the mucosal immune system.

Their position relates them to an epithelial antigen-entry interface.

They illustrate that mucosal immunity includes discrete organized structures.

Mucosal epithelium

External antigen

Subepithelial lymphoid cells / antigen-presenting cells

Anatomically defined mucosal tissue: Pharyngeal tonsil

Barrier-associated immune tissue · schematic

Slide 43 · Peyer patches are discrete intestinal lymphoid tissue

Peyer patches are organized mucosal lymphoid tissue in the intestine.

They exemplify lymphoid architecture associated with the gut barrier.

They belong to the mucosal rather than primary lymphoid category.

Mucosal epithelium

External antigen

Subepithelial lymphoid cells / antigen-presenting cells

Organized intestinal lymphoid tissue: Peyer patches

Barrier-associated immune tissue · schematic

Slide 44 · Mucosal tissues contain many lymphocytes

A large proportion of the body’s lymphocytes may be within mucosal tissues.

This reflects the substantial extent of mucosal surfaces and tissue.

The distribution underscores why mucosal immune responses are anatomically important.

Extensive mucosal tissue

Large lymphocyte pool

Barrier surveillance

Immune

Function

Conceptual relationship · schematic

Slide 45 · Memory cells are abundant at mucosal sites

Many lymphocytes resident in mucosal tissues have memory phenotypes.

Their presence is compatible with repeated environmental antigen exposure.

The source notes their prevalence, without specifying a numerical proportion.

Naive-cell survey

Secondary organs

Search for antigen

Mucosal memory

Barrier-associated tissue

Previously primed lymphocytes

Parallel pathways · schematic

Slide 46 · Cutaneous immune tissue is situated under the skin

Cutaneous lymphoid components lie beneath the skin epithelium.

They respond to antigens gaining access through epithelial breaches.

Epidermal Langerhans cells are a dendritic-cell population relevant to antigen sampling.

Skin epithelium

External antigen

Subepithelial lymphoid cells / antigen-presenting cells

Entry across epithelium → local antigen sampling and response

Barrier-associated immune tissue · schematic

Slide 47 · Epithelial capture and lymphoid activation are linked

Dendritic cells at or below epithelial entry sites capture antigens.

The cells may migrate in lymph to draining lymph nodes.

Node T-cell zones provide the subsequent antigen-presentation environment.

Barrier breach

Tissue antigen capture

DC transport in lymph

Node T-cell activation

Functional sequence · schematic

Slide 48 · Peripheral immune organs are tailored to antigen routes

Nodes are optimized for lymph-borne antigens.

Spleen surveys blood-borne antigens.

Barrier-associated tissues respond beneath mucosal and cutaneous epithelium.

Site

Anatomical input

Principal context

Lymph node

Lymphatic drainage

Tissue-derived antigen

Spleen

Circulating blood

Blood-borne antigen

Barrier tissue

Across epithelium

Mucosal or skin response

Slide 49 · Lymphocyte recirculation connects immune locations

Lymphocytes continuously move between blood and specific tissues.

Naive lymphocytes pass through secondary lymphoid organs.

Effector cells can travel to sites where infection and inflammation are present.

Blood

Secondary lymphoid tissue

Activation

Inflamed tissue

Functional sequence · schematic

Slide 50 · Naive and effector lymphocytes follow different goals

Naive lymphocytes move through organs where antigen is concentrated.

Effector lymphocytes migrate to sites requiring microbial elimination.

Circulation is organized around cell function rather than random redistribution.

Naive lymphocyte

Antigen search

Secondary lymphoid organs

Effector lymphocyte

Microbial elimination

Infection / inflammation site

Parallel pathways · schematic

Slide 51 · T-cell recirculation is functionally essential

Naive T cells must search secondary-organ sites for presented antigen.

Effector T cells need access to infected tissues to act on microbes.

This is why the source places particular emphasis on T-cell recirculation.

Naive T cell

Secondary immune organ

Antigen encounter

Effector T cell

Infected peripheral tissue

Microbial control

Parallel pathways · schematic

Slide 52 · Plasma cells use a different distribution strategy

Plasma cells can remain in lymphoid organs and bone marrow.

They secrete antibodies that circulate in blood to distant sites.

Unlike effector T cells, antibody-producing cells need not reach each infected tissue.

Effector T cell

Cell migrates to infection

Local contact-dependent work

Plasma cell

Antibodies travel in blood

Distant humoral action

Parallel pathways · schematic

Slide 53 · Dendritic cells are positioned for naive T-cell priming

They are frequent at epithelial and interstitial sites of antigen entry.

Microbial signals promote their movement to lymphoid T-cell zones.

They display protein-derived antigen with abundant MHC and activation molecules.

Tissue dendritic cell

Microbial antigen captured

Migration to T-cell zone

Naive T-cell activation

Functional sequence · schematic

Slide 54 · Follicular dendritic cells support B-cell responses

FDCs are specialized fibroblasts within follicles and germinal centers.

They retain antibody- or complement-associated antigen using Fc and C3b receptors.

Their interaction supports selection of B cells with higher antigen affinity.

Immune complexes

Captured by FDC

B-cell antigen recognition

High-affinity B-cell survival

Functional sequence · schematic

Slide 55 · Conventional DCs and FDCs are fundamentally different

Conventional DCs present processed antigens to T lymphocytes.

FDCs retain antigen complexes and make them available to B lymphocytes.

Despite their names, FDCs are not the cells that prime naive T cells.

Aspect

Conventional dendritic cell

Follicular dendritic cell

Main location

T-cell area

Follicle / germinal center

Key function

T-cell antigen presentation

Antigen retention for B cells

Identity

Myeloid APC

Specialized fibroblast

Slide 56 · Macrophages contribute at several immune stages

Ingestion and processing allow macrophages to present peptide antigens to T cells.

T-cell activation can increase macrophage killing of ingested microbes.

Macrophages also ingest microbes coated with IgG or C3b.

Antigen presentation

T-cell-enhanced killing

Opsonized microbe removal

Immune

Function

Conceptual relationship · schematic

Slide 57 · A macrophage can present ingested antigen to a T cell

Macrophages phagocytose microbes or protein antigens.

Processed peptide fragments can be presented to T lymphocytes.

This connects innate microbial ingestion with adaptive immune recognition.

Microbe engulfed

Peptide processing

Antigen presentation

T-cell recognition

Functional sequence · schematic

Slide 58 · T lymphocytes can amplify macrophage microbicidal action

Certain cell-mediated responses are directed against intracellular microbes.

Activated T cells stimulate macrophages.

Activated macrophages are more effective at killing ingested organisms.

Intracellular microbe

T-cell response

Macrophage activation

Enhanced killing

Functional sequence · schematic

Slide 59 · Opsonization improves macrophage phagocytosis

Antibody IgG or complement fragment C3b may coat a microbe.

Macrophages efficiently ingest and destroy coated microbes.

This is an effector link between humoral immunity and innate phagocytes.

IgG / C3b binds microbe

Opsonized microbe

Macrophage ingestion

Destruction

Functional sequence · schematic

Slide 60 · Application: A microbe enters damaged skin

A skin breach introduces microbial antigen into underlying tissue.

Dendritic cells and lymph drainage can convey antigen toward a regional node.

A draining lymph node is the expected major site of initiating an adaptive response.

Reasoning prompt

Antigen enters a peripheral tissue through damaged skin. Which secondary organ first concentrates the draining antigen?

Anatomical inference

The regional draining lymph node—tissue antigens reach it via lymphatic drainage and/or migrating DCs.

Slide 61 · Application: Microbial antigen circulates in blood

The anatomic route is blood, not lymph from a single tissue site.

Splenic macrophages and dendritic cells encounter circulating antigen.

The spleen is the relevant organ for blood-borne adaptive immune initiation.

Reasoning prompt

A microbial antigen is distributed through the bloodstream. Which peripheral organ is anatomically specialized to sample it?

Anatomical inference

The spleen—splenic blood channels expose circulating antigens to macrophages and dendritic cells.

Slide 62 · Application: A follicle develops a pale center

A responding B-cell follicle may form a central germinal center.

Follicular dendritic cells support B-cell responses at this site.

A follicular pattern should not be confused with the adjacent T-cell-rich paracortex.

Reasoning prompt

A schematic lymph-node follicle now contains a central germinal center. Which lymphocyte compartment is responding?

Anatomical inference

The B-cell follicle—germinal-center formation is associated with recent follicular antigen response.

Slide 63 · Application: Identify the T-cell-rich nodal region

The cortex contains B-cell follicles.

The paracortex is rich in T cells and conventional dendritic cells.

A location adjacent to follicles therefore points to the T-cell compartment.

Reasoning prompt

An antigen-presenting dendritic cell interacts with a naive T cell beside cortical follicles. Name the nodal region.

Anatomical inference

Paracortex—the lymph-node T-cell zone, adjacent to the cortical B-cell follicles.

Slide 64 · Application: Why plasma cells need not migrate

Plasma cells can remain in bone marrow or lymphoid organs.

Their secreted antibodies circulate to distant sites via blood.

Effector T cells, in contrast, must often reach infected tissue.

Reasoning prompt

A plasma cell stays in marrow despite an infection elsewhere. Why can it still contribute to host defense?

Anatomical inference

It secretes antibodies distributed through blood; The cell itself need not reach the site of infection.

Slide 65 · Organ, input and lymphocyte territory must be linked

Node: Lymphatic input; Follicles contain B cells and paracortex contains T cells.

Spleen: Blood input; Follicles contain B cells and PALS contains T cells.

Barrier tissue: Subepithelial sampling, including organized mucosal structures.

Tissue

Input route

Characteristic T/B arrangement

Lymph node

Lymphatic

Paracortex / cortical follicles

Spleen

Blood

PALS / white-pulp follicles

Mucosa or skin

Barrier epithelium

Subepithelial immune populations

Slide 66 · Five principles explain the tissue organization

Primary tissues generate antigen-responsive T and B lymphocytes.

Secondary tissues concentrate antigen and surveying naive lymphocytes.

T- and B-cell neighborhoods organize different phases of immunity.

Lymph nodes sample lymph; Spleen samples blood; Barriers host local immunity.

Recirculation delivers naive cells to antigen and effectors to sites of action.

Generate

Concentrate

Partition

Circulate

Immune

Function

Conceptual relationship · schematic

Slide 67 · Source and scope

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

Chapter 6: Diseases of the Immune System—“Tissues of the Immune System,” p. 174–175.

Immediately preceding “Myeloid Cells” section supplies DC, FDC and macrophage context.

Anatomical diagrams are original editable teaching schematics, not histologic specimens.

Core source

Primary and secondary immune tissues

Adjacent context

Dendritic cells and macrophages