cDNA clones encoding rabbit immunoglobulin λ chains. Evidence for length variation of the third hypervariable region and for a novel constant region

Abstract

Five cDNA clones designated pDH2, pDH8, pDH9, pDH31 and pDH101 encoding rabbit immunoglobulin .lambda. light chain sequences have been characterized. Comparison of the V.lambda. sequences suggests that, in addition to an increased divergence in all of the complementarity-determining regions (CDRs), variable-region diversity is amplified by the length heterogeneity of the CDR3, at the V.lambda.-J.lambda. junction. An insertion of four codons at positions 48a-d has been noted in three cDNA sequences. This insert, not found in .lambda. nor .kappa. light chains of other species, has a variable sequence, suggesting its possible implication in expanding variability of the CDR2. One of the cDNA clones was shown to encode a novel C.lambda. region which differs by four amino acid substitutions from the C.lambda. region common to all the other clones. Thus, the rabbit can use two different C.lambda. genes, which might correlate with the expression of the two known allotypes of .lambda. chains, C7 and C21. Southern blotting experiments indicate a small number of germ-line V.lambda. genes and the cDNA nucleotide sequence data reported here suggest that several of these genes can be expressed. The possibility of at least two V-J-C gene clusters is discussed.