Surrogate light chain expression is required to establish immunoglobulin heavy chain allelic exclusion during early B cell development

Allelic exclusion at the IgH locus was examined in B lineage cells of wild-type mice and mice unable to express the surrogate light chain molecule λ5 using a single-cell PCR approach. By analyzing B precursor cells containing two V(H)D(H)J(H) rearrangements, we found that in wild-type animals, cells are allelically excluded as soon as μ chains are expressed. Furthermore, we provide evidence that in cells expressing Dμ proteins V(H) → D(H)J(H) rearrangement is inhibited. In contrast, in the absence of λ5 protein, B precursor cells were allelically 'included,' indicating that allelic exclusion at the IgH locus requires expression of the pre-B cell receptor either containing a, μ chain or a Dμ chain. However, although μ chain double-producing B precursor cells are generated in λ5-deficient mice, such cells were not detected among surface immunoglobulin positive B cells.