MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-II AND COMPLEMENT POLYMORPHISMS IN POSTPARTUM THYROIDITIS

The objective was to re-evaluate the association between class II HLA- DR and DQ MHC antigens and postpartum thyroiditis (PPT) and to determi ne the prevalence of the class III complement allotypes of Properdin f actor B (Bf), C4A and C4B in this condition, Two hundred and sixty-fiv e (of 2897) pregnant women screened positive for thyroid autoantibody activity took part, Further blood samples were obtained for HLA class II (185) and complement (193) typing. The severity of the ensuing PPT was assessed by measuring thyroid function during the postpartum year. The HLA-DR and DQ phenotypes were assigned from restriction fragment length polymorphism analysis, and Bf, C4A and C4B allotypes were deter mined by immunofixation with anti-Bf or anti-C4 antibodies after elect rophoresis. A weak association between the HLA class II antigens and P PT, as indicated by a reduced frequency of DR15 and DQ6 together with an increased frequency of DR5 and DQ7, was confirmed. However, only th e change in DR5 frequency remained significant after correction (corre cted p < 0.05). Postpartum thyroiditis was also associated with freque ncy disturbances in Bf and C4A allotypes but not C4B allotypes. Whilst this study has not provided evidence of a strong marker gene for PPT, it does not preclude the involvement of the MHC in this condition. Th ese data show disturbances in complement allotype frequencies, suggest ing that the class III region may provide a useful focus for further s tudy of this pathology.