Organization of the lymphoid organs and tissues

DC mackrophage

MYELOID PRECURSOR

BONE MARROW

HSC HEMATOPOIETIC STEM CELL

mast

DC monocyte neutrophilmast

neutrophil

TISSUES

BLOOD

B-cell T-cell

T-cellNK-cell

THYMUS

B-cell

LYMPHOIDPRECURSOR

LYMPHOID TISSUES

BLOOD

Blood circulation

Macrophage

Hassal’s corpuscle

Dendritic cell

Thymocytes

Epithelial cells

CapsuleSeptum

Mature naive T- lymphocytes

STRUCTURE OF THE THYMUS

STRUCTURE OF THE THYMUS

THYMUS INVOLUTION

PERIPHERAL LYMPHOID ORGANS

Sites of lymphocyte activation and differentiation

SpleenLymph nodesEpithelial cell – associated lymphoid tissues

Skin-associated lymphoid tissue (SALT)Mucosa-associated lymphoid tissue (MALT)

Gut-associated lymphoid tissue (GALT)Bronchial tract-associated lymphoid tissue

(BALT)

Organization (levels) of immunocytes

Diffuse cells

Follicle

organ

Patch

Lymph nodes are communication centers within the immune systemLymph nodes are communication centers within the immune systemThey form a unified, interconnected system via circulation They form a unified, interconnected system via circulation

of blood and lymphof blood and lymph

Fluid from tissues is collected by venules and lymphatic capillaries

Activation of adaptive immune response I.

Activation of adaptive immune response II.

5. Medullary cords (Macrophage & plasma cell area)

Medullary sinus

6. Efferent lymphatic vessel

Artery

Vein

4. Germinal centre (site of intense B cell proliferation)

3. Secondary lymphoid follicle

Paracortical(T cell) area

2. Primary Lymphoid follicle (B cell area)

1. Afferent lymphatic vessel. Lymph, Ag, & cells with captured Ag drained from tissues enters here

Lymph node

medulla

veinarthery

Collagen capsule

Marginal sinus

Paracortex Cortex

Trabecula

High endothelial venule (HEV)

Afferent lymph

Efferent lymph

Primary follicle

B CELLS

Secondory follicle

GerminalCenter (GC)

B CELLS

B CELLST CELLS

STRUCTURE OF LYMPH NODES

mature,naiveB-sejt

FDC

Plasma cell

Memory B cell

Mature,naive B cell

Naive B lymphocytes enter lymph nodes Naive B lymphocytes enter lymph nodes via HEVvia HEV

B cells are reqruited to HEV from the B cells are reqruited to HEV from the blood by CCL21 chemokine secreted by blood by CCL21 chemokine secreted by

stromal cellsstromal cells

CCL21 and CCL19 chemokines attract B CCL21 and CCL19 chemokines attract B lymphocytes to the lymph nodelymphocytes to the lymph node

HOMING OF B LYMPHOCYTES IN HOMING OF B LYMPHOCYTES IN LYMPH NODESLYMPH NODES

Subcapsular sinusValve

Capsule

Cortex

Trabecula

Follicles Medullary cords

Medullary sinuses

Capsule

LymphaticArtery and vein

Blood & Lymphatic vessels

STRUCTURE OF THE SPLEEN

STRUCTURE OF THE SPLEEN

NO LYMPHOID CIRCULATION

Filtration of blood borne antigens

Red pulp

Marginal zone

Marginal sinus

B cell corona

Germinal centre

Periarteriolar lymphocyticsheath (PALS) – T cell area

Central arteriole

Spleen white pulpTransverse section

MMALTALT

Most pathogens attack mucosal epitheliaMost pathogens attack mucosal epithelia

Covered by mucus containing glycoproteins, proteoglycans, Covered by mucus containing glycoproteins, proteoglycans, enzymesenzymes Antimicrobial peptides protect against physical damage and Antimicrobial peptides protect against physical damage and infectioninfection

Thin dynamic layers covering large areasThin dynamic layers covering large areas

Well protected by the immune systemWell protected by the immune system

More lymphocytes are assigned to the mucosal surfaces than to More lymphocytes are assigned to the mucosal surfaces than to the rest of the bodythe rest of the body

Peyer’s patches

Dome area Villi

GC

Gut-associated lymphoid tissuesGut-associated lymphoid tissues

Peyer’s patches 5-100 follicles forming a dome structurePeyer’s patches 5-100 follicles forming a dome structureM-cells: microfold cells --- no glycocalyx – antigen uptakeM-cells: microfold cells --- no glycocalyx – antigen uptake

Transport of antigens via M cells

Dendritic cells of the lamina propria outside Peyer’s patchescapture antigens by samlpeing the gut lumen directly

Intraepithelial lymphocytes

Large number of intraepithelial lymphocytes are present in gut epthelia