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