Monoclonal antibody TG1 recognizes specifically antigens HLA-B27, B7, B22 and B17 on cell surface in cytotoxicity and cytofluorometry tests. When cell detergent extracts were subjected to SDS PAGE under mild conditions (no heating and no reduction of the sample) followed by Western blotting, TG1 detected 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 samples were boiled prior to SDS PAGE, TG1 detected again the 43 kDa free heavy chains of B7, B22 and B17 but no zone corresponding to B27 could be detected indicating that the epitope in free B27 chains is more sensitive to denaturation by SDS. Thus, our main finding is that the interaction of HLA-B27 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)-microglobulin complex to the SDS dissociation is strikingly similar to the behavior of MHC class II molecules under similar conditions. Thus, it may be speculated that HLA-B27 complexes can be also more stable than other MHC class I molecules under more physiological dissociative conditions (e.g. in endosomal compartments). This feature might potentially influence antigen presentation by HLA-B27 and contribute to the well known disease linkage of HLA-B27.