The formation and selection of cells expressing preB cell receptors and B cell receptors.

Abstract

The repertoires of B cell receptor (Ig)-expressing B cells are generated during B cell development in a stepwise fashion (Tonegawa 1983). First, DH segments are rearranged to JH segments on the H chain locus at the transition from B220+CD19- proB cells to B220+CD19+ckit+ preB-I cells. In most preB-I cells both H chain alleles are DHJH-rearranged (Rolink et al. 1995). PreB-I cells, as proB cells, express the VpreB and λ5 proteins of the surrogate L chain (Melchers et al. 1993) and the preB cell — and B cell — receptor-anchoring proteins Igα and Igβ (Reth 1994). Next, VH segments are rearranged to DHJH segments (Alt et al. 1984) at the transition from preB-I to preB-II cells (ten Boekel et al. 1995). Whenever this rearrangement occurs in-frame, a μH chain can be expressed. Productive VHDHJH- rearranged H chain alleles are found in large, cycling ckit- CD25+ preB-II cells which, like all subsequent stages of B cell development, all express an H chain in their cytoplasm (Rolink et al. 1994). One fifth of all large preB-II cells express the μH chains as complexes with surrogate L chains as so-called preB cell receptors on their surface (Winkler et al. 1995). In these cells the L chain loci remain in germline configuration, and are not transcribed. The other portion of the large preB-II cells appears further progressed in development. They no longer express the preB cell receptor, in fact, they have the expression of the surrogate L chain genes downregulated, and begin to transcribe L chain loci (Grawunder et al. 1995). A small fraction of preB-II cells expressing μH chains in their cytoplasm continues to express ckit and surrogate L chain, but fails to express preB cell receptors on their surface. Their properties are described below.KeywordsMouse Bone MarrowChain LocusAllelic ExclusionPrimary Lymphoid OrganChain Gene RearrangementThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.