Vitamin C Modulates the Immunotoxic Effect of 17α-Methyltestosterone in Nile Tilapia

The synthetic androgen 17 alpha-methyltestosterone (MT) is profusely used and practically needed in the production of all-male Nile tilapia fry; however, such androgenic hormones badly disrupt the immune system. This study aimed to alleviate or counteract the immunotoxic effect of MT using vitamin C (ascorbic acid or vit C). Our results show that the highest phagocytic activity (PA), phagocytic index (PI), and lysozyme activity were detected in the vit C group and the MT plus vit C group. Furthermore, PA and PI were significantly suppressed, but lysozyme activity was stronger in the MT group than in the control. No differences were detected in the differential leukocyte count among the studied groups. Moreover, vit C obviously reduced the upregulated expression level of the innate immune-related genes, interleukin 1 beta (il1 beta) interleukin 8 (il8), tumor necrosis factor alpha (tnf alpha), CC-chemokine, Toll-like receptor 7 (tlr7), immunoglobulin M (IgM) heavy chain, and cellular apoptosis susceptibility (cas) induced by MT, excluding tnf alpha in the liver and CC-chemokine and tlr7 in the kidney. The micronucleus frequency was found to significantly improve in the vit C plus MT group in comparison to that in the MT group. Normal histoarchitecture of the liver, kidney, and spleen was observed in all the groups, except for the frequently observed melanomacrophage centers in the spleen and kidney of the fish that were treated with vit C and vit C plus MT. More importantly, our findings demonstrate that the upregulation of immune-related genes is not necessarily a sign of a stimulated or enhanced immune system.