The preparation and characterization of anti-peptide heteroantisera recognizing subregions of the intracytoplasmic domain of class I H-2 antigens

Peptides corresponding to each of the three intracytoplasmic exons (i.e. exons 6, 7 and 8) of the murine class I H-2K b gene were synthesized, coupled to bovine serum albumin and used as immunogens in rabbits. In each case the antisera were found to react with the immunizing peptide coupled to a heterologous carrier, and recognized class I heavy chains electrophoretically transferred from SDS-polyacrylamide gels to nitrocellulose. Immunoprecipitation of class I antigens from Nonidet P-40 (NP-40) solubilized EL-4 (H-2 b) tumour cells by each of the antisera reflected their ability to recognize the corresponding determinants in non-denatured class I molecules. The same sera were also able to immunoprecipitate class I molecules from NP-40 solubilized RDM-4 (H-2 k) and P815 (H-2 d) tumour cells, indicating the cross-reactive nature of these antisera for different class I alleles. In addition to reacting with the class I heavy chain in its conventional form as a dimer with β 2-microglobulin, the antiserum specific for the exon 8 peptide was able to react with “free” (i.e. non- β 2-microglobulin-associated) class I heavy chains. Thus, a unique set of immunological reagents has been prepared which offer a new approach to studying the structural and functional features of the cytoplasmic domain of class I H-2 antigens.