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 1st 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