Immunoglobulins iii, b cell development: overview hypermutation. B cell development has two phases (see fig. Antigen independent: (bone marrow), v(d)j and allelic exclusion. Antigen dependent: (elsewhere), clonal selection, class switching, Pro-b to pre-b also has loss of cd43 marker: pre-b cell receptor complex. Vpreb and l 5 are surrogate light chains, help heavy chains fold. Required to progress to pre-b cell, otherwise apoptosis: two types of b cells. Cd5+ in body fluids, sigm and cd19+, secrete lots of igm, anti-self. Antigen-dependent development of b cells: b cell activation and differentiation, t cell independent: relies on crosslinking of sigm on b cells, t cell dependent: T helper cell and b cell interact to activate b cell. Activated b cells differentiate into memory and plasma (ab secreting) cells: class switching. Directed by interleukins secreted by t cells (e. g. il-4 gives igg1 and ige) Upstream switch region transcripts are necessary: affinity maturation. Occurs in germinal center also: immunologic memory.