Multiple levels of selection responsive to immunoglobulin light chain and heavy chain structures impede the development of Dmu-expressing B cells.

The truncated/V(H)-less mouse H chain Dmu forms precursor B cell receptors with the surrogate L chain complex that promotes allelic exclusion but not other aspects of pre-B cell development, causing most progenitor B cells expressing this H chain to be eliminated at the pre-B cell checkpoint. However, there is evidence that Dmu-lambda1 complexes can be made and are positively selected during fetal life but cannot sustain adult B lymphopoiesis. How surrogate and conventional L chains interpret Dmu's unusual structure and how that affects signaling outcome are unclear. Using nonlymphoid and primary mouse B cells, we show that secretion-competent lambda1 L chains could associate with both full-length H chains and Dmu, whereas secretion-incompetent lambda1 L chains could only do so with full-length H chains. In contrast, Dmu could not form receptors with a panel of kappa L chains irrespective of their secretion properties. This was due to an incompatibility of Dmu with the kappa-joining and constant regions. Finally, the Dmu-lambda1 receptor was less active than the full-length mouse mu-lambda1 receptor in promoting growth under conditions of limiting IL-7. Thus, multiple receptor-dependent mechanisms operating at all stages of B cell development limit the contribution of B cells with Dmu H chain alleles to the repertoire.

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