Principles of Immunology Organs of the Immune System 1/31/06 “There are two ways to slide easily through life. Believe everything or doubt everything. Both ways save us from thinking.” A Korzybski
Word List Antigenic commitment Clonal proliferation GALT Lymph Lymphocyte activation MALT Peyer’s patches Primary lymphoid organs Secondary lymphoid organs Self antigens
Lymphoid System Primary lymphoid organs Bone marrow Thymus Secondary lymphoid organs Organized Lymph nodes Spleen Less organized
Lymphatic System Network of vessels Collects fluid from tissues Major cell is lymphocyte Unidirectional Often first place where antigens are detected
Thymus Structure Gross Bi-lobed Lies above heart Microscopic Capsular Lobules with outer cortex and inner medulla
Thymus Function Takes in immature T cells and puts out mature (immunocompetent) T cells Increased diversity of T cells T cell selection
Thymus T cell selection Based on MHC/Ag complex recognition Recognize MHC/Non self AG complexes Recognize MHC/Self Ag complexes Do not recognize MHC/Ag complexes Athymic condition Natural Other
Bone marrow Structure Microscopic Less well defined than thymus Role of stromal cells Function Hematopoiesis B cell maturation B cell selection Puts out mature, naive B cells
Lymph Nodes Structure Gross Bean-shaped structures Drains major segments of lymphatic system
Lymph Nodes Structure Microscopic Major cell types Lymphocytes Macrophages Dendritic cells Cortex/paracortex/medulla Follicles Primary Secondary
Lymph Nodes Function 1 st line of response to antigens Secondary follicle (Germinal center) is site of B cell proliferation, mutation, differentiation Specificity is high >90% of B cells die through apoptosis After Ag stimualtion lymphocyte numbers up by 50X in efferent lymphatic vessel Lympadenopathy
Spleen Structure Gross Ovoid organ in upper left quadrant of abdomen Microscopic Compartmentalized Red pulp White pulp Periarticualr lymphoid sheath Site of Ag presentation Major cell types Lymphocytes Macrophages Dendritic cells RBCs
Spleen Function Filters out older RBCs Responds to Ag in circulatory system Produces activated B cells Splenectomy
Tonsils Follicular structure Contains lymphocytes, macrophages, mast cells Germinal centers appear in response to Ag Protective role in URI
Appendix Associated with intestines Responds to Ag Role in GI immune response
MALT Lymphoid tissues below epithelium Presence of B cells Ag presented through unique cell (M cell) Preferentially responds with IgA antibody