Abstract
There is a well documented association between rheumatoid arthritis (RA) and the HLA-DR4 and DRw53 in many racial groups. Recently, much interest in the genes and their products in HLA class III region has been generated by their possible involvement in the development of autoimmune diseases including systemic lupus erythematosus. In this study, the allotypes of complement C4A, C4B and properdin factor B, which are coded for by genes in the class III region, were investigated in Japanese RA patients and controls. The frequency of C4B5 was significantly higher in RA patients, especially in male as compared with female patients, than that of the controls. Since a strong linkage disequilibrium among genes of C4B5, DR4 and DRw53 is reported in Japanese, and since RA patients in other ethnics are not associated with C4B5, the allotype, C4B5, will not have a direct role for the development of RA. We further analysed restriction fragment length polymorphisms of the genes in the HLA class III region in RA patients and controls by Southern blot method using C4 or 21-hydroxylase cDNA probe and restriction enzymes, such as BamHI, TaqI, HindIII and KpnI. When the C4 probe was used, HindIII 6.0 and 10kb fragments were observed only in C4B5-positive persons including patients and controls. Some of the RA patients were deficient for TaqI 6.0kb fragment which was present in all of the controls tested. However, we could not identify any specific bands for RA patients.
