Effect of cyclosporin A on spontaneous autoimmune thyroiditis of Obese strain (OS) chickens

The spontaneous autoimmune thyroiditis (SAT) which develops in the Obese strain (OS) of chickens depends on an intact B-dependent portion of immune system. T helper cells have been shown to be required for the production of thyroglobulin autoantibodies (Tg-AAb), but a possible contribution of cytotoxic T cells in the initial phases of SAT still remains to be elucidated. Cyclosporin A (CsA), an immunosuppressive drug with selective activity on T blast formation was used as a probe to clarify this issue: (a) the immunosuppressive potential of CsA was first verified for an avian species by demonstrating prolongation of skin allograft survival; (b) posthatching treatment of OS chickens with CsA until they were killed at 3 weeks of age did not alter the frequency and severity of SAT and the incidence and titer of Tg-AAb; (c) treatment of OS embryos on days 15, 17 and 19 of incubation entailed the development of significantly more severe disease and higher titers of Tg-AAb as compared to controls. A possible effect of CsA on precursors of suppressor T cells in the chicken is postulated. Cytotoxic T cells seem to play a minor role in the beginning of thyroid infiltration. It is concluded that CsA may not be the drug of choice for treatment of at least some autoimmune diseases.