The kappa gene repertoire of human neonatal B cells

Abstract

The kappa chain repertoire of individual IgD + human neonatal B cells was analyzed using a single cell PCR technique. A total of 104 productive and 90 non-productive VκJκ rearrangements from three cord blood B cell samples were sequenced and compared to the adult IgM + peripheral B cell VκJκ repertoire. All six Vκ families were present in neonatal B cells, but the distribution was not random. In the non-productive repertoire Vκ2 and Vκ6 families were less frequent, Vκ1 and Vκ3 families were as frequent, and Vκ4 and Vκ5 families were more frequent than expected from random chance. Notably, the Vκ2 family was negatively selected into the productive repertoire. In contrast, the Vκ1 family was positively selected because of positive selection of three specific genes, O12/O2, L12a and L9. B3 (Vκ4) and B2 (Vκ5) were over-represented in the non-productive repertoire and then were expressed less frequently in the productive repertoire. In contrast, the Vκ3 family gene, A27, was also over-represented in the non-productive repertoire but not further selected into the productive repertoire. Compared to the adult repertoire, junctional diversity was less marked because of a diminished influence of TdT activity, whereas the mean CDR3 length was comparable to that of normal adult B cells. Comparison of the distribution of Vκ and Jκ genes with those found in normal adult subjects suggested that there was less receptor editing in neonatal B cells. When neonatal CD5 + B cells were compared with CD5 − IgD + B cells, it was noted that the Vκ gene A30 was used only in CD5 + B cells in both the productive and non-productive repertoires. The results indicate that the usage of Vκ genes by neonatal B cells is biased by both intrinsic molecular processes and selection. The evidence of selection indicates that the Vκ repertoire is shaped by self antigens, since exposure to exogenous antigens is limited at the time of birth.