cDNA clones encoding immunoglobulin λ chains from rabbit expressing the phenotype c7

A cDNA library derived from spleen cells of an unimmunized rabbit expressing the c7 phenotype of Igλ chains (c7+, c21−) was screened with Vλ or Cλ probes of a λ light chain bearing c21 epitopes. The nucleotide sequences of three hybridizing clones were found to be identical within the Vλ, Jλ and Cλ regions. The Vλ region was 97% similar to that of the functional germ-line gene Vλ2, and the Cλ region was identical to that of gene Cλ6, recently identified. Gene Cλ6 exhibited four codon differences when compared with gene Cλ5, 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 Cλ6 encodes the C region of c7 λ chains and that c7 and c21 markers designate two distinct isotypic forms of λ chains. On the basis of comparative Southern blotting analyses and restriction maps of cloned genomic regions containing Vλ and Cλ genes, a scheme is proposed to account for the c7− and c21− phenotypes.