RESUMEN
We examined the effect of 17alpha-ethinylestradiol on immunity of the Western fence lizard, Sceloporus occidentalis. Injection of 17alpha-ethinylestradiol resulted in dose-dependent suppression of peripheral blood leukocyte levels as determined by cell counts, whereas total spleen cell levels were decreased only at higher doses of 17alpha-ethinylestradiol. In contrast, spleen cell proliferation was enhanced by 17alpha-ethinylestradiol as measured by reduction of MTT to formazan following a two-way mixed lymphocyte reaction. Antibody responses were unaffected. Effects on peripheral blood leukocyte levels and spleen cell proliferation similar to those observed in response to injection of 17alpha-ethinylestradiol were observed following injection of a single dose of hydrocortisone. However, injection of lizards with 17alpha-ethinylestradiol did not result in a significant increase in serum cortisol. Results of this study suggest that exposure of Western fence lizards to 17alpha-ethinylestradiol leads to decreased numbers of circulating leukocytes and total spleen cell numbers and the enhancement of spleen cell proliferation in a two-way mixed lymphocyte reaction. These effects probably involve mechanisms other than or in addition to the induction of cortisol release.