cDNA clones encoding immunoglobulin lambda chains from rabbit expressing the phenotype c7.

A cDNA library derived from spleen cells of an unimmunized rabbit expressing the c7 phenotype of Ig lambda chains (c7+, c21-) was screened with V lambda or C lambda probes of a lambda light chain bearing c21 epitopes. The nucleotide sequences of three hybridizing clones were found to be identical within the V lambda, J lambda and C lambda regions. The V lambda region was 97% similar to that of the functional germ-line gene V lambda 2, and the C lambda region was identical to that of gene C lambda 6, recently identified. Gene C lambda 6 exhibited four codon differences when compared with gene C lambda 5, the latter encoding c21 epitopes. The data presented here and in the accompanying report (Jaton, J.-C. et al., Eur. J. Immunol. 1990, 20:2713) support the view that gene C lambda 6 encodes the C region of c7 lambda chains and that c7 and c21 markers designate two distinct isotypic forms of lambda chains. On the basis of comparative Southern blotting analyses and restriction maps of cloned genomic regions containing V lambda and C lambda genes, a scheme is proposed to account for the c7- and c21- phenotypes.