Secondary (2°) Lymph Organs

• Ranges from:1. Diffuse assemblages of lymphocytes and MØ (in lung

and intestinal wall) referred to as MALT and GALT to

2. Lymphoid follicles surrounded by draining lymph vessels to

3. Lymph nodes and spleenGreater organization

Lymph nodes:

Divided into 3 distinct regions:

Cortex – w/ 1° follicles composed of APC’s

Paracortex – w/T cells and DC’s w/ hi levels of MHC II

Medulla – w/ plasma cells producing Ab’s

Afferent vessels

Efferent vessel

Lymph nodes

• Initial activation of B cells is thought to occur in paracortex

• w/i 4-7 days, a few B cells and TH cells migrate to 1° follicles of cortex form 2° follicles

Spleen• Major role in IR’s to Ag’s in blood

• Response center for systemic infections

• Blood enters via splenic artery

• Organ separated into regions of red pulp and white pulp

Spleen • Red pulp consists of sinuses w/ MØ’s, RBC’s

site of RBC destruction/ removal

• White pulp contains PALS w/ 1 follicles surrounded by lympho-cytes, MØ, and DC’s

Mucosal-associated lymphoid tissue (MALT)

• Combined surface area of mucus membrane = 400 m2 (size of basketball court)

• Major sites of entry

• Protected by loose assemblage of organized lymphoid tissues (MALT)

• Tonsils

• Peyer’s patches

MALT (cont’d)

• Each with groups of 30-40 lymphoid follicles