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