Estradiol increases susceptibility of goldfish to Trypanosoma danilewskyi.

We examined the in vivo and in vitro effects of estradiol on the host defense of goldfish against a hemoflagellate Trypanosoma danilewskyi. Estradiol (10(-6) M), significantly suppressed the mitogen-induced proliferation of peripheral blood lymphocytes in vitro. The parasitemia and mortality of goldfish implanted with tubing containing estradiol were significantly higher than that of sham operated control fish. In addition, the mitogen-induced proliferation of peripheral blood lymphocytes obtained from estradiol-implanted fish was significantly impaired when compared to that of lymphocytes obtained from untreated sham operated control fish. Estradiol implantation did not influence the ability of goldfish to resist a challenge infection with T. danilewskyi. These results indicate that estradiol can modulate the susceptibility to hemoflagellates by suppressing the host immune response.