Scientific Publications by FDA Staff

BMC Immunol 2014 Oct 30;15:51

Multiple factors influence the contribution of individual immunoglobulin light chain genes to the naive antibody repertoire.

Fitzsimmons SP, Aydanian AG, Clark KJ, Shapiro MA

BACKGROUND: The naive antibody repertoire is initially dependent upon the number of germline V(D)J genes and the ability of recombined heavy and light chains to pair. Individual VH and VL genes are not equally represented in naive mature B cells, suggesting that positive and negative selection also shape the antibody repertoire. Among the three member murine Vkappa10 L chain family, the Vkappa10C gene is under-represented in the antibody repertoire. Although it is structurally functional and accessible to both transcriptional and recombination machinery, the Vkappa10C promoter is inefficient in pre-B cell lines and productive Vkappa10C rearrangements are lost as development progresses from pre-B cells through mature B cells. This study examined VH/Vkappa10 pairing, promoter mutations, Vkappa10 transcript levels and receptor editing as possible factors that are responsible for loss of productive Vkappa10C rearrangements in developing B cells. RESULTS: We demonstrate that the loss of Vkappa10C expression is not due to an inability to pair with H chains, but is likely due to a combination of other factors. Levels of mRNA are low in sorted pre-B cells and undetectable in B cells. Mutation of a single base in the three prime region of the Vkappa10C promoter increases Vkappa10C promoter function in pre-B cell lines. Pre-B and B cells harbor disproportionate levels of receptor-edited productive Vkappa10C rearrangements. CONCLUSIONS: Our findings suggest that the weak Vkappa10C promoter initially limits the amount of available Vkappa10C L chain for pairing with H chains, resulting in sub-threshold levels of cell surface B cell receptors, insufficient tonic signaling and subsequent receptor editing to limit the numbers of Vkappa10C-expressing B cells emigrating from the bone marrow to the periphery.