Strong association of HLA-B27 heavy chain with beta(2)-microglobulin

Monoclonal antibody TG1 recognizes specifically antigens HLA-B27, B7, B22 a nd B17 on cell surface in cytotoxicity and cytofluorometry tests. When cell detergent extracts were subjected to SDS PAGE under mild conditions (no he ating and no reduction of the sample) followed by Western blotting, TG1 det ected exclusively a complex of B27 heavy chains with beta (2)-microglobulin (as a 50 kDa band) whereas the other B-locus antigens (B7, B22, B17) were detected as free 43 kDa heavy chains under the same conditions. When the sa mples were boiled prior to SDS PAGE, TG1 detected again the 43 kDa free hea vy chains of B7, B22 and B17 but no zone corresponding to B27 could be dete cted indicating that the epitope in free B27 chains is more sensitive to de naturation by SDS. Thus, our main finding is that the interaction of HLA-B2 7 heavy chain with beta (2)-microglobulin appears to be stronger than that of the other HLA-B chains. The resistance of the HLA-B27/beta (2)-microglob ulin complex to the SDS dissociation is strikingly similar to the behavior of MHC class II molecules under similar conditions. Thus, it may be specula ted that HLA-BZ: complexes can be also more stable than other MHC class I m olecules under more physiological dissociative conditions (e.g. in endosoma l compartments). This feature might potentially influence antigen presentat ion by HLA-B27 and contribute to the well known disease linkage of HLA-B27. (C) American Society for Histocompatibility and Immunogenetics, 2000. Publ ished by Elsevier Science Inc.