Principles of Immunology Organs of the Immune System

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 o o o o o Antigenic commitment Clonal proliferation GALT Lymphocyte activation MALT Peyer’s patches Primary lymphoid organs Secondary lymphoid organs Self antigens

Lymphoid System o Primary lymphoid organs n n o Bone marrow Thymus Secondary lymphoid organs n Organized o o n Lymph nodes Spleen Less organized

Lymphatic System o Network of vessels n n Collects fluid from tissues Major cell is lymphocyte Unidirectional Often first place where antigens are detected

Thymus o Structure n Gross o o n Bi-lobed Lies above heart Microscopic o o Capsular Lobules with outer cortex and inner medulla

Thymus o Function n Takes in immature T cells and puts out mature (immunocompetent) T cells Increased diversity of T cells T cell selection

Thymus o T cell selection n Based on MHC/Ag complex recognition o o Recognize MHC/Non self AG complexes Recognize MHC/Self Ag complexes Do not recognize MHC/Ag complexes Athymic condition n n Natural Other

Bone marrow o Structure n Microscopic o Less well defined than thymus o o Role of stromal cells Function n n Hematopoiesis B cell maturation B cell selection Puts out mature, naive B cells

Lymph Nodes o Structure n Gross o o Bean-shaped structures Drains major segments of lymphatic system

Lymph Nodes o Structure n Microscopic o Major cell types n n n o o Lymphocytes Macrophages Dendritic cells Cortex/paracortex/medulla Follicles n n Primary Secondary

Lymph Nodes o Function n n n 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 50 X in efferent lymphatic vessel Lympadenopathy

Spleen o Structure n Gross o n Ovoid organ in upper left quadrant of abdomen Microscopic o Compartmentalized n n o Periarticualr lymphoid sheath n o Red pulp White pulp Site of Ag presentation Major cell types n n Lymphocytes Macrophages Dendritic cells RBCs

Spleen o Function n o Filters out older RBCs Responds to Ag in circulatory system Produces activated B cells Splenectomy

Tonsils o o Follicular structure Contains lymphocytes, macrophages, mast cells Germinal centers appear in response to Ag Protective role in URI

Appendix o o o Associated with intestines Responds to Ag Role in GI immune response

MALT o o Lymphoid tissues below epithelium Presence of B cells Ag presented through unique cell (M cell) Preferentially responds with Ig. A antibody