1. Organization of the lymphoid organs and tissues

2. HEMATOPOIETIC STEM CELL
BONE MARROW
HSC
HEMATOPOIETIC STEM CELL
MYELOID
PRECURSOR
THYMUS
B-cell
LYMPHOID
PRECURSOR
NK-cell
T-cell DC
neutrophil
monocyte
mast
BLOOD
BLOOD
TISSUES
LYMPHOID TISSUES
neutrophil
B-cell
T-cell
mast
mackrophage DC

4. STRUCTURE OF THE THYMUS Mature naive T- lymphocytes
Capsule
Septum
Blood circulation
Epithelial cells
Thymocytes
Dendritic cell
Macrophage
Hassal’s corpuscle
Mature naive T- lymphocytes

5. STRUCTURE OF THE THYMUS

6. THYMUS INVOLUTION

7. PERIPHERAL LYMPHOID ORGANS
Sites of lymphocyte activation and differentiation
Spleen
Lymph nodes
Epithelial 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)

8. Organization (levels) of immunocytes
Diffuse cells
Follicle
Patch
Follicle. Organized cylyndrical clusters of lymphocytes.
Patches: follicles gathered in groups
Organ: organized groups of follicles encapsulated. Supporting tissues
organ

9. Lymph nodes are communication centers within the immune system
They form a unified, interconnected system via circulation
of blood and lymph

10. Fluid from tissues is collected by venules and lymphatic capillaries

11. Activation of adaptive
immune response I.

12. Activation of adaptive
immune response II.

13. Lymph node 4. Germinal centre (site of intense B cell proliferation)
5. Medullary cords
(Macrophage &
plasma cell area)
3. Secondary
lymphoid follicle
6. Efferent lymphatic
vessel
2. Primary Lymphoid
follicle (B cell area)
Artery
Paracortical
(T cell) area
Vein
Medullary sinus
90% of lymphocytes come from the blood, only 10 % from the lymph.
1. Afferent lymphatic
vessel. Lymph, Ag, & cells with captured Ag drained from tissues enters here

14. STRUCTURE OF LYMPH NODES
Collagen capsule
Marginal sinus
Paracortex
Cortex
Trabecula
Secondory follicle
Germinal
Center (GC)
B CELLS
Afferent lymph
Efferent lymph
Plasma cell
Memory B cell
Mature,naive B cell
Primary follicle
B CELLS
High endothelial venule (HEV)
T CELLS
B CELLS
STRUCTURE OF LYMPH NODES

15. HOMING OF B LYMPHOCYTES IN LYMPH NODES
Naive B lymphocytes enter lymph nodes via HEV
B cells are reqruited to HEV from the blood by CCL21 chemokine secreted by stromal cells
CCL21 and CCL19 chemokines attract B lymphocytes to the lymph node

16. Capsule
Subcapsular sinus
Valve

17. Capsule
Trabecula
Follicles
Medullary cords
Cortex
Medullary sinuses

18. Blood & Lymphatic vessels
Artery and vein
Lymphatic

19. STRUCTURE OF THE SPLEEN

20. NO LYMPHOID CIRCULATION Filtration of blood borne antigens
STRUCTURE OF THE SPLEEN
NO LYMPHOID CIRCULATION
Filtration of blood borne antigens

21. Spleen white pulp Transverse section Marginal sinus B cell corona
Red pulp
Germinal centre
Marginal zone
Periarteriolar lymphocytic
sheath (PALS) – T cell area
Central arteriole

22. MALT Most pathogens attack mucosal epithelia
Covered by mucus containing glycoproteins, proteoglycans, enzymes
Antimicrobial peptides protect against physical damage and infection
Thin dynamic layers covering large areas
Well protected by the immune system
More lymphocytes are assigned to the mucosal surfaces than to the rest of the body

23. Peyer’s patches

24. Dome area
Villi GC

25. Gut-associated lymphoid tissues
Peyer’s patches follicles forming a dome structure
M-cells: microfold cells --- no glycocalyx – antigen uptake

26. Transport of antigens via M cells

27. Dendritic cells of the lamina propria outside Peyer’s patches
capture antigens by samlpeing the gut lumen directly

28. Intraepithelial lymphocytes
Large number of intraepithelial lymphocytes are
present in gut epthelia
Intraepithelial lymphocytes