Studies on the interaction between alpha-gliadin and HLA and T cell receptor molecules in coeliac disease

Coeliac disease has a known strong linkage with the HLA complex and has also recently been linked to the T cell receptor genes but the mechanism whereby these genes confer susceptibility is not known. This study has examined two possible mechanisms: (i) direct, lectin-like binding of alpha-gliadin (the causative agent of CD) to HLA or TcR molecules and (ii) antigenic cross-reactivity between alpha-gliadin and HLA or TcR molecules. A flow cytometer was used to assess interactions between alpha-gliadin, anti-alpha-gliadin antibodies (raised in both coeliac patients and in rabbits) and EBV-transformed B cell lines from coeliac patients and HLA-matched and mismatched normal controls. The B cell lines were shown to express HLA-DP, -DQ and -DR antigens which are also found on coeliac intestinal epithelial cells. After incubating B cell lines with alpha-gliadin over a wide range of concentrations, no binding of alpha-gliadin to any of the cell lines could be detected with either of the gliadin-specific antibodies. This suggests that HLA molecules do not bind to alpha-gliadin in a lectin-like fashion. In contrast to the B cell lines, alpha-gliadin binding to peripheral blood monocytes could be demonstrated. This binding occurred equally to patient and control monocytes and was not influenced by HLA allotype. The second possibility tested was that alpha-gliadin and the disease-associated HLA molecule bear antigenic similarities. However, neither rabbit anti-gliadin serum nor purified human alpha-gliadin antibody bound directly to the B cell lines. Using peripheral blood T cells similar results were obtained; no binding of alpha-gliadin or antibodies to alpha-gliadin was found. Thus this study shows that the HLA and TcR associations with CD are not explained by the direct binding of alpha-gliadin to these molecules nor by a sharing of antigenic determinants between alpha-gliadin and these molecules.