BIOL 1103 Lecture Notes - Immunoglobulin Class Switching, Somatic Hypermutation, Immunoglobulin G
30 Jan 2013
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Role: produce clonally diverse lymphocytes with broad but tolerant ag: primary lymphoid organs recognition, bone marrow. Site of initial production of all hematopoietic cells. Stromal cells provides support and cytokines for hematopoiesis: b-lymphopoiesis. Full progression from stem cell to mature sig+ b cell. Vectoral (precursors found at periphery whereas mature cells are. B cell loss through bad rearrangements and negative selection (clearance through macrophages: t-lymphopoiesis. Cd7+ stem cell proceeds to pro-thymocyte, which travels to: thymus (see diagram p. 315) Medullary epithelium cells and macrophages (also at cmj) are negative in the center) thymus selecting. B cell that encounters correct ag proliferates and secretes unmodified igm. Direct th2-b cognate interaction activates b cell, germinal center. B cell proliferates as centroblast (dark zone), ig hypermutation and class switching occurs. Centrocytes (nondividing, light zone) undergo selection towards affinity maturation; the ig they produce has to be higher affinity than that in ag/ab complex presented by fdc. Eventual differentiation into plasma and memory cells.
