Identification of three distinct allelic forms of bovine CD4

The CD4-specific monoclonal antibody (mAb) CC26, when tested on a total of 143 cattle, failed to react with T cells from 16% of animals and gave reduced intensity staining in a further 35% of animals. The results of family studies with groups of half- and full-siblings indicated that CC26 recognizes an allele of CD4 which is co-dominantly expressed in heterozygous animals. This was confirmed by sequential immunoprecipitation and by selecting transfectants expressing the CC26+ and CC26- allelic forms of CD4 following transfection of genomic DNA from a heterozygous animal. Biochemical studies also revealed an allelic difference in the relative molecular weight (M(r)) of the CD4 molecule, one allele giving 49,000/52,000 MW bands and the other 52,000/57,000 MW bands in sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Treatment of CD4+ cell lines with tunicamycin resulted in the appearance of a 47,000 MW band for both allelic forms indicating that the difference in M(r) is due to glycosylation. All of the CC26+ alleles examined were of the low molecular weight form (M(r)low) whereas both M(r)low and M(r)high alleles were represented in CC26- animals. Thus, on the basis of M(r) and reactivity with mAb CC26, three allelic forms of bovine CD4 can be identified, namely CC26+ M(r)low, CC26- M(r)low and CC26- M(r)high; it is proposed that these alleles are designated CD4.1, CD4.2 and CD4.3, respectively. The allelic difference detected by CC26 was present in both Bos taurus and B. indicus cattle indicating that it had arisen prior to divergence of these subspecies. The M(r)high allele (CD4.3) was detected only in B. indicus animals.