Lymphoid Organs Flashcards
Secondary Lymphoid Organs
MALT
Spleen
Lymph Nodes
Primary Lymphoid Organs
BM and Thymus
Adaptive Immunity
Occurs after 1-6 days; mediated by B-cells and T-cells activated by macrophage products
N-terminal regions
“Variable regions”
Composed of variable heavy an light chains
IgE
Secreted; binds to mast cells
*Parasitic infxns and allergic rxn
IgM
Largest Ab; secreted as a pentamer and found in membranes
*Contains B-cell Ag receptors
IgD
Membrane Ig; contains B-cell Ag receptor
IgG
Primary Ig found in serum; responsible for adaptive “memory” and neonatal immunity
*Also important in phagocytosis (marks Ags)
IgA
Secreted dimer found in mucous membranes
T-Cell Antigen Receptor
Have a single Ag binding site w/ both alpha and beta chains
*Recognizes small peptides on the surface of APCs
Clonal Expansion
B-cells recognize an Ag, produce clones of plasma cells that secrete Ab to destroy foreign substance
B-cells
Use membrane bound antibodies to recognize a variety of epitopes; can turn into plasma cells
T-cell Selection
Positive: Cells w/ useful Ag receptors
Negative: Cells that react too strongly and can’t differentiate self
*This process peaks from birth-puberty
Blood-thymus barrier
Prevents exposure of immature T-cells to foreign Ags
-Formed by endothelial cells w/ tight jnxns and thick basal lamina
MALT
Collections of lymphoid cells that are adjacent to mucous and exposed to the external environment; has high concentrations of IgA
*Found in the GI, respiratory, and reproductive tracts
High Endothelial Venules
Location @ which lymphocytes enter lymph nodes from blood vessels
*Tall, cuboidal epithelia
Spleen
Removes aged/damaged RBCs an activates B-lymphocytes
Peyer’s Patches
Lymph nodes found in the lamina propria and sub-mucosa of the ileum
Germinal Centers
Location where lymphocyte proliferation occurs
*Spleen may not have them
Location of T-cells in Lymphatic Nodules
Paracortex
Hassall’s Corpuscles
Key histological feature of the thymus; found in the medulla of the thymus
Red pulp
Dense, reticular fibers of the spleen that contain RBCs, WBCs, and other cells that remove aged RBCs
Splenic cords
Aggregations of lymph tissue found in the red pulp
Venous sinuses
Dilated vessels w/ cuboidal epithelial cells found in the red pulp
IgA secretion
IgA binds to polyIg receptors on mucosal cells, is internalized and transported across the cell where it is cleaved and released into the lumen of the organ
White Pulp
Aggregations of lymph nodes found in the trabeculae of the spleen
