SELECTION AGAINST N-REGION DIVERSITY IN IMMUNOGLOBULIN HEAVY-CHAIN VARIABLE REGIONS DURING THE DEVELOPMENT OF PREIMMUNE B-CELL REPERTOIRES

The generation of Ig heavy chain chain diversity is dependent on the ordered rearrangement of three different, i.e. variable (V(H)), diversity (D(H)), and joining (J(H)), germline gene segments, exonuclease nibbling of the terminals of these gene segments, and the addition of template-independent nucleotide (N-sequences) in the junctions of these segments. The latter process has recently been reported to be limited within B cells formed during early ontogeny. In this study, we have analysed a large number of V(H)DJ(H) rearrangements isolated from genomic DNA of adult and neonatal C57Bl/6 mice using the polymerase chain reaction (PCR) technique. A comparison of functional versus non-functional V(H)DJ(H) rearrangements derived from these PCR libraries, or from a set of previously published clones of BALB/c origin, revealed a selection against N-region diversity both in neonatal and adult B cell repertoires. This selection process is most pronounced in the early development of the immune system but can still be observed in the adult. Furthermore, selection against N-sequence additions was evident amongst neonatal V(H)DJ(H) rearrangements utilizing both V(H) 7183 and V(H) J558 genes, but only in V(H) 7183 utilizing clones of adult origin. These results imply that in addition to a developmentally controlled onset of N-sequence additions, cellular selection against N-region diversity exist both in the neonatal and adult immune system.