The epitope recognized by pan-HLA class I-reactive monoclonal antibody W6/32 and its relationship to unusual stability of the HLA-B27/beta 2-microglobulin complex

A broadly used pan-HLA class I-reactive monoclonal antibody W6/32 is believ ed to recognize a conformational epitope dependent on association between h eavy chains and beta (2)-microglobulin (beta (2)m). However, in the present study we report that W6/32 does recognize at least some free HLA class I h eavy chains under the partially denaturating conditions of nonreducing West ern blotting, namely nearly all HLA-B allelic products. Furthermore, we con firm, and largely extend our previous observation that complexes of beta (2 )m with heavy chains of a few HLA class I allelic forms (most notably HLA-B 27) exhibit unusual resistance to dissociation by SDS, which is reminiscent of MHC class II molecules. In addition, our data indicate the existence of covalent (disulfide-linked) heterodimers of certain HLA class I heavy chai ns (namely Cw1 and Cw4) and beta (2)m.