1. 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 spleen Greater organization

2. 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

3. Lymph nodes Initial activation of B cells is thought to occur in paracortex w/i 4-7 days, a few B cells and T H cells migrate to 1° follicles of cortex  form 2° follicles

4. 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

5. 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

6. Mucosal-associated lymphoid tissue (MALT) Combined surface area of mucus membrane = 400 m 2 (size of basketball court) Major sites of entry Protected by loose assemblage of organized lymphoid tissues (MALT) Tonsils Peyer’s patches

7. MALT (cont’d) Each with groups of 30- 40 lymphoid follicles