The swine Ig heavy chain locus has a single JH and no identifiable IgD

Abstract

Sequence analysis of 84 V region cDNAs expressed with IgM, IgG and IgA from both adult and newborn swine suggested that their J_H segments had been derived from the same germline J_H. Only a single hybridizing J_H segment could be identified in genomic DNA, in a J_h-C_μ cosmid and in a Sacl fragment of the cosmid extending 5 kb 5' of the Enh_H. The single germline J_H segment mapped 6 kb 5' to C_μ. This J_H had a sequence identical to 40 of 42 J_H segments expressed in a newborn piglet and 25 of 42 expressed by adult swine. None of the 19 J_H segments which varied from the germline sequence were identical to each other and half of the nucleotide changes were silent. No cosmid DNA hybridizing with heterologous probes for C_δ could be found within 20 kb 3' of C_μ and C_δ could not be cloned from genomic or cDNA libraries. A conserved IgD fragment could be amplified from human, mouse and rat genomic DNA but not from rabbit, swine or cattle. We hypothesize that heavy chain organization and constituency in homeothermic vertebrates is correlated with the site of secondary antibody repertoire development and the mechanism(s) used.