Reproductive consequences of an immune challenge during the preovulatory period in trout: possible mediatory role of tumor necrosis factor α
The relevance of immune-endocrine interactions to the regulation of ovarian steroidogenesis in teleost is virtually unexplored. However, it is known that, as part of the innate immune response during infection, a number of cytokines and other immune factors are produced and act on the reproductive system. In the present study, we have studied the effects of lipopolysaccharide (LPS) administration in preovulatory females and have observed a significant advance in the timing of ovulation coupled with a lower survival of the resulting embryos. Furthermore, we have investigated the effects of recombinant brook trout TNFα, as a potential mediator of the effects of LPS, on granulosa cell viability, gene expression in follicular layers and steroid production. Our results suggest that TNFα decreases granulosa cell viability and stimulates the expression of genes known to be involved in the normal ovulatory process in trout. TNFα also stimulates testosterone production by theca layers. In view of these results, we propose that a pathogen-induced activation of the immune system prior to ovulation could increase TNFα-mediated apoptosis in the trout ovary, advance ovulation and result in a potentially important decrease in egg quality.