Molecular mechanisms and selection influence the generation of the human VλJλ repertoire

To define the A light chain repertoire in humans, a single-cell PCR technique using genomic DNA obtained from individual peripheral B cells was employed. Of the 30 known functional Vλ genes, 23 were detected in either the nonproductive or productive repertoires. Specific Vλ genes, including 2A2, 2B2, 1G, and 4B, were overexpressed in the nonproductive repertoire, whereas some Vλ genes, such as 3R, 2A2, 2B2, 1C, 1G, and lB, were overexpressed in the productive repertoire. Comparison of the nonproductive and productive repertoires indicated that no Vλ genes were positively selected, whereas a number of Vλ genes, including 4C, 1G, 5B, and 4B, were negatively regulated. All four of the functional Jλ segments were found in both repertoires, with Jλ7 observed most often. Evidence of terminal deoxynucleotidyltransferase activity was noted in nearly 80% of nonproductive VλJλ rearrangements, and exonuclease activity was apparent in the majority. Despite this, the mean CDR3 length was 30 base pairs in both productive and nonproductive repertoires, suggesting that it was tightly regulated at the molecular level. These results have provided new insights into the dimensions of the human Vλ repertoire and the influences that shape it.