[A model and 3 examples for understanding HLA and diseases: cis and trans complementation of MHC class II in juvenile insulin-dependent diabetes, juvenile rheumatoid arthritis and celiac disease].

The heterozygous effect observed for the HLA and disease association in insulin dependent diabetes, juvenile rheumatoid arthritis and coeliac disease is interpreted in the view of recent cellular and molecular data of MHC class II molecules demonstrating the existence of hybrid HLA DQ molecules and conformational determinants created by Trans (or Cis) complementation. It is postulated that unique determinants created de novo by such mechanisms represent the structural basis for the altered immune response leading to the pathogenesis of these auto-immune diseases.