Effect of sex-steroid hormones, testosterone and estradiol, on humoral immune parameters of gilthead seabream

The role of sex-steroid hormones, testosterone (T) and 17β-estradiol (E2), on the humoral immune parameters of the teleost gilthead seabream Sparus aurata was studied attempting to deepen on the knowledge of the immune–reproductive system interactions. Fish were injected intraperitoneally with coconut oil containing different dosages of T (0, 2, or 5 μg g−1 body weight [bw]) or E2 (0, 1, or 2 μg g−1 bw) and sampled 1, 3, and 7 days later. Hormonal levels and immune parameters (complement, peroxidase and antiprotease activities and IgM levels) were determined in plasma. Plasma hormone levels peaked at 1 day post-injection decreasing thereafter. Treatment with T significantly increased both complement and peroxidase activities after 3 days of injection but antiprotease activity and IgM levels remained unchanged. Treatment with E2 enhanced complement activity 1 day post-injection while decreased it after 3 and 7 days. However, peroxidase activity increased at 3 and 7 days post-injection while total IgM levels decreased. Implications of T and E2 in the immune-reproductive system interactions were discussed.