Various V‐J rearrangement efficiencies shape the mouse λ B cell repertoire

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Abstract
The diversity of the B cell repertoire of Cx knockout mice is limited by the expression of four λ light chain types. Among the spleen B cells, λ1 is expressed by the majority (58%) of cells, and λ3 by the minority (8%), while λ2(V2) and λ2(Vx) are expressed in intermediate quantities (18% and 16%, respectively). To assess the influence of mechanistic pressures on the λ subtype distribution, the proportions of the different λ rearrangements were determined in various B cell subpopulations divided on the basis of the λ subtype expressed, and the VλJλ junction sequences were studied at different steps of B cell differentiation (pre‐B, immature and mature B cells). The data show that (1) the ratio of productive/non‐productive VJ junctions is determined by the nature of the λ segments that are rearranged as can be observed in the pre‐B cells, (2) V1‐J1 non‐productive rearrangements are often found in the λ1‐negative B cells in the periphery, and (3) V1J3 junctions are often non‐productive regardless of the nature of the cells analyzed. Our results, therefore, suggest that a strong probability of initiating a V1‐J1 rearrangement and a weak probability of giving a productive V1J3 junction are responsible for the λ1 dominance and the λ3 under‐expression, respectively. The intermediate proportion of λ2(V2) subtype is most likely due to a probability of obtaining a productive joint that is better than that for V1J3 and a probability of initiating a rearrangement that is lower than that for V1J1. However, the λ2(Vx) cell proportion cannot be determined only by these parameters.