Seasonal changes and human chorionic gonadotrophin (hCG) effects on innate immune genes expression in goldfish (Carassius auratus)

• Innate immune genes increase during the breeding season in goldfish.
• Increasing expression levels are induced by hCG.
• Female goldfish were found to be more responsive than male goldfish.

We profiled the expression of a group of proinflammatory immune genes, comprising TNFα-1, TNFα-2, IFN-γ, IL1β-1, IL1β-2, CCL-1, and CXCL-8 in liver, head kidney, gills, and spleen of goldfish, during the reproductive cycle and in response to injection of the hormone human chorionic gonadotrophin (hCG). Most genes showed higher expression during the breeding season in both sexes. However, activation of immune responses was much stronger in female goldfish. Injection with hCG, an analog of luteinizing hormone (LH), which is involved in numerous reproductive functions, markedly changed gene expression in most studied organs, in both male and female goldfish. Again, female goldfish were found to be more responsive than male goldfish. The strongest activation of these genes was seen 7 days post-injection; the effect was dose dependent with a lower dose being in general more effective. For several of the genes, the gills were the most responsive tissue and, in male goldfish, gills were often the only responsive tissue, suggesting an important immunological role for gills during breeding. The data suggest that increasing expression levels are regulated by LH arising during the breeding season, with greater sensitivity in female goldfish than in male goldfish. These data support an interaction between the innate immune system and the reproductive axis.