Differential immune responses to excretory–secretory antigens of lung-stage larvae of Schistosoma mansoni in mice and rats

In contrast to mice, rats are less-susceptible to infection with Schistosoma mansoni, perhaps mounting protective immune responses that provide a microenvironment unfavorable for the normal growth and survival of the parasite. Upon infection, schistosomular excretory–secretory products (ESP) trigger T helper (Th) effector cells and polarize the immune microenvironment. We investigated the differences in mouse and rat immune responses to the larval ESP, 14-3-3-like protein, P18, and fructose-1,6-bisphosphate aldolase, prepared in a recombinant or multiple antigen peptide form. Ex vivo spleen cells (SC) of naïve, and 7 day-S. mansoni-infected CD1 mice and Wistar rats were stimulated in vitro with the selected ESP, and the culture supernatants were assessed for cytokine levels by capture enzyme-linked immunosorbent assay. S. mansoni ESP failed to induce SC of 7 day-infected mice to produce detectable interleukin (IL)-4 levels, but led to significant increase in released interferon-gamma (IFN-γ) as compared to naïve mice. Conversely, SC of rats released significant IL-4 levels in response to ESP stimulation, while IFN-γ was hardly detected in the supernatants. Amounts of ESP-specific antibodies in infected rats were significantly higher than in infected mice. Our results suggest that resistance to schistosomiasis is associated with type 2 cytokines and high levels of parasite ESP-specific antibodies.