Transcript Organs of the Immune System 01/31/06

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
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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
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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
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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
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Red pulp
White pulp
 Periarticualr lymphoid sheath
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Site of Ag presentation
 Major cell types
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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