BOLA CLASS-I CHARGE HETEROGENEITY REFLECTS THE EXPRESSION OF MORE THAN 2 LOCI

Internationally recognized allo-antisera in lymphocyte microcytotoxici ty assays are thought to detect allelic products of a single highly po lymorphic class I locus. A recent report suggested that two bovine lym phocyte antigen (BoLA) class I loci are expressed at the protein level . However, 1D-IEF analysis of BoLA class I molecules reveals multi-ban d patterns which cannot be reconciled with the reported number of loci . The aim of this study was to investigate the origins of the charge d iversity of BoLA class I molecules observed using 1D-IEF. BoLA class I molecules appear to be glycosylated at a single N-linked position wit h a complex type carbohydrate moiety which has up to three terminal si alic acid residues. Class I molecules immunoprecipitated from resting bovine PBL are not phosphorylated. Neither modification is responsible for the observed charge heterogeneity. Peptide mapping reveals that d ifferent BoLA charge variants have distinct digestion patterns. Furthe rmore, a number of different polypeptides are associated with each ser ological specificity. These polypeptides appear to be encoded by diffe rent loci which exist in linkage disequilibrium. The number of charge variants with different peptide maps indicates that the BoLA system ha s a minimum of three class I loci expressed at the protein level.