James Goding; Week 10 MED1011; Immunology
Plasma cells are mature B cells. Thymus and bone marrow are primary lymphoid organs and are where lymphocytes undergo maturation. Mature lymphocytes move to secondary lymphoid organs (spleen, lymph nodes). T cells from thymus, B from bone marrow. Activated lymphocytes carry out functions in secondary lymphoid organs and in tissues. Both H and L chains contribute to antigen binding. Light chains are kappa or lambda, heavy are IgM, E, G, D, A. Heavy chains can have specific variations. IgM is first to be made, interacts with complement, large. IgG is most common, crosses placenta, interacts with complement. IgA is found in secretions (milk, bile, saliva). IgE is minor class, binds to mast cells, causes allergic responses. IgD is minor class, only found on the surface of B cells.
Affinity is dependant on hypervariable chains. Fc portion is used in phagocytosis, transporting blood from mother to baby through placenta (Fc receptor), binds to IgE to cause degranulation and allergic responses. Antigen fitting receptor causes proliferation and secretion. Clonal downsizing results in some memory cells that proliferate in further infection. There are about 50 genes in each light chain region and 50 in each heavy, 2500 variations occur. Mutations can also be a factor. Tolerance is learnt by removing self-reactive cells in bone marrow and thymus.