The role of testosterone in spontaneous autoimmune thyroiditis of Obese strain (OS) chickens

We have recently reported a two-fold defect in glucocorticoid mediated immunoregulation in the Obese strain (OS) of chickens with spontaneous autoimmune thyroiditis (SAT): (i) a decreased basal corticosterone (CN) tonus due to an elevation of plasma corticosteroid-binding globulin (CBG) and (ii) an impaired CN rise in response to antigenic stimuli as well as lymphokines produced after mitogenic stimulation. The aim of the present study was to investigate the pathophysiological relevance of testosterone for the development of SAT. Compared to healthy normal White Leghorn chickens (NWL) the basal sex hormone tonus as well as androgen receptors of bursal tissue are not altered in the OS. Administration of sheep red blood cells (SRBC) or lymphokine containing conditioned media not only increased CN plasma levels but concomitantly modulated testosterone serum concentrations, although in an inverse direction and without significant difference between OS and healthy control chickens. These results suggest that, in contrast to the glucocorticoid system, androgen tonus as well as its modulation by immune signals are normal in the OS. The mode of action by which androgens exert their known beneficial effect on the development of SAT was also studied. According to our findings the capacity of testosterone to prevent SAT when administered during the posthatching period can be attributed to direct effects on bursal epithelial cells as well as indirect mechanisms, namely a fall in CBG levels leading to normalization of the CN tonus.