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Organization of the lymphoid
organs and tissues
BONE MARROW
HSC
MYELOID
PRECURSOR
HEMATOPOIETIC STEM CELL
LYMPHOID
PRECURSOR
BLOOD
BLOOD
DC
monocyte mast neutrophil
TISSUES
DC
THYMUS
mackrophage mast neutrophil
B-cell
NK-cell
T-cell
LYMPHOID TISSUES
B-cell
T-cell
STRUCTURE OF THE THYMUS
Capsule
Septum
Blood
circulation
Epithelial cells
Thymocytes
Dendritic cell
Macrophage
Mature naive T- lymphocytes
Hassal’s corpuscle
STRUCTURE OF THE THYMUS
THYMUS INVOLUTION
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)
Organization (levels) of immunocytes
Diffuse cells
Follicle
Patch
organ
Lymph nodes are communication centers within the immune system
They form a unified, interconnected system via circulation
of 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.
Lymph node
4. Germinal centre
(site of intense
B cell proliferation)
3. Secondary
lymphoid follicle
2. Primary Lymphoid
follicle (B cell area)
Paracortical
(T cell) area
1. Afferent lymphatic
vessel. Lymph, Ag, &
cells with captured Ag
drained from tissues
enters here
5. Medullary cords
(Macrophage &
plasma cell area)
6. Efferent lymphatic
vessel
Artery
Vein
Medullary sinus
Marginal sinus
Secondory
follicle
Afferent lymph
Primary follicle
B CELLS
Germinal
Center (GC)
B CELLS
medulla
High endothelial
venule (HEV)
Trabecula
Collagen capsule
Paracortex
Cortex
mature,naive
Mature,naive
BB-sejt
cell
FDC
Efferent lymph
vein
arthery
B CELLS
T CELLS
Memory B cell
Plasma cell
STRUCTURE OF LYMPH NODES
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
Capsule
Subcapsular sinus
Valve
Capsule
Trabecula
Medullary cords
Follicles
Cortex
Medullary sinuses
Blood & Lymphatic vessels
Artery and vein
Lymphatic
STRUCTURE OF THE SPLEEN
STRUCTURE OF THE SPLEEN
NO LYMPHOID CIRCULATION
Filtration of blood borne antigens
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
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
Peyer’s patches
Dome area
Villi
GC
Gut-associated lymphoid tissues
Peyer’s patches 5-100 follicles forming a dome structure
M-cells: microfold cells --- no glycocalyx – antigen uptake
Transport of antigens via M cells
Dendritic cells of the lamina propria outside Peyer’s patches
capture antigens by samlpeing the gut lumen directly
Large number of intraepithelial lymphocytes are
present in gut epthelia
Intraepithelial lymphocytes