The level of lambda 1 light chain expression in the mouse reflects the probability of rearrangement of the relevant gene.

The predominance of kappa over lambda light chain expression in mice can either reflect the probability of rearrangement of the relevant locus or be the result of antigen-driven clonal expansion. To discriminate between these two possibilities we determined, by limiting dilution analysis, the frequencies of kappa- and lambda-producing cells in B lymphocytes generated in vitro from bone marrow pre-B cells. The frequencies obtained in these cultures are not significantly different from those obtained with mature spleen cells. In addition, Southern blot analysis of bone marrow-derived and splenic cell DNA revealed that in both populations the extent of B lymphocytes having undergone lambda 1 gene rearrangement does not exceed 4%. These results, therefore, establish that in the mouse the low level of lambda light chain expression directly reflects the probability of rearrangement of the relevant locus.