THYROIDITIS IN THE BB RAT IS ASSOCIATED WITH LYMPHOPENIA BUT OCCURS INDEPENDENTLY OF DIABETES

The spontaneously diabetic BB rat is an excellent and well studied mod el for human insulin-dependent diabetes (IDDM), sharing many important features with the human disease. Similarities include an equal freque ncy of IDDM in males and females, production of antibodies against pan creatic cell antigens, and an MHC disease association. In addition, th e BB rat shares with human IDDM patients an increased frequency of aut oantibodies against the parietal cells of the stomach and colloid cell s of the thyroid gland. Here we investigate the genetic basis of thyro iditis in the BB rat. Based on crosses between BB, Lewis and Fischer r ats, we show that two susceptibility factors for diabetes-the lymphope nia trait present in diabetes prone BB rats and the MHC-also appear to be risk factors for thyroiditis. However, the nature of the susceptib ility was different for the two autoimmune diseases, with lymphopenia being absolutely required for diabetes although it only conferred incr eased risk for thyroiditis. Also, in contrast to IDDM, the MHC conferr ed dominant susceptibility to thyroiditis. Despite these shared risk f actors, diabetes per se did not show significant correlation with thyr oiditis. (C) 1995 Academic Press Limited