Excretory-secretory products from the parasite Schistocephalus solidus modulate threespine stickleback splenocytes

Helminths can modulate the immune systems of their hosts through the release of soluble molecules known as excretory-secretory products (ESPs). To better understand the extent and mechanisms behind helminth-mediated immunosuppression, we used an emerging model of immunoparasitology, threespine stickleback, Gasterosteus aculeatus, and its tapeworm parasite Schistocephalus solidus. We examined the impacts of exposure to ESPs of S. solidus (SsESPs) originating from Canadian lakes on the viability of threespine stickleback splenocytes in vitro. We found that exposure to SsESPs from Gosling Lake significantly increased overall splenocyte viability with the greatest impact on the granulocyte population. Interestingly, exposure to heat-inactivated Gosling Lake SsESPs increased live granulocyte and lymphocyte populations. These results, however, appear to be population-specific, as SsESPs derived from Nimpkish Lake cestodes dampened splenocyte viability. The observed increase in live splenocytes with Gosling Lake SsESPs contrasts with previous studies demonstrating that SsESPs can suppress head kidney leukocyte (HKL) viability, which suggests that S. solidus-derived ESPs may have cell- or tissue-specific immunomodulatory effects and highlights the importance of studying host-parasite interactions across diverse immune tissues.