EVIDENCE THAT THE V-KAPPA-III GENE USAGE IS NONSTOCHASTIC IN BOTH ADULT AND NEWBORN PERIPHERAL B-CELLS AND THAT PERIPHERAL CD5-CELLS ARE OLIGOCLONAL( ADULT B)

There is evidence that in certain situations the expressed antibody re pertoire is dominated by small subsets of V gene segments. They includ e fetal, CD5+, and autoantibody-forming B cells as well as low grade B cell malignancies. For instance, inside the VKIII family of similar t o 10 members, only 3 (humkv325, 328, and Vg) are used recurrently for autoantibody production. However, the significance of this recurrence is difficult to interpret without a clear vision of the actual reperto ire in normal subjects. To address this, we have sequenced and compare d two sets of rearranged VKIII genes generated by cDNA PCR amplificati on from a normal newborn, a normal adult, and from CD5+ B cells of the same adult donor. The results show that: (a) only four VKIII gene seg ments are used by neonatal and total adult B cells (kumkv325, humkv328 , Vg, and kv305), humkv325 being overexpressed in both repertoires; (b )there is no significant difference in terms of VKIII gene usage betwe en the adult and newborn repertoires; (c) regarding the junction regio ns, there is a favored use of the most 5' J(K), gene segments (Jk1-Jk2 ); similar to 20% of the newborn and adult junction sequences was char acterized by one or two additional codons, most probably resulting fro m a nontemplate addition of nucleotides; (d) adult clones, in contrast to most newborn clones, show sequence divergences from prototype sequ ences with patterns which suggest antigen-driven diversity; (e) regard ing the adult CD5+ B cell library, it is most probable that the 78 clo nes analyzed derived from no more than nine different V-K-J(K) rearran gements. Humkv325 is used by at least six of them, and most of the exp ressed V genes were in exact or very near germline configuration. Coll ectively these results suggest that the expressed antibody VKIII reper toire in the adult represents only a fraction of the potential genetic information and that it resembles the preimmune repertoire of the neo nate. The data, which also suggest that the adult peripheral blood CD5 + B cell population may be dominated by a small number of B cell clone s, are discussed with regards to the VKIII usage in pathological situa tions.