Investigation of defense response and immune priming in Biomphalaria glabrata and Biomphalaria straminea, two species with different susceptibility to Schistosoma mansoni.

For many years, the immune response of invertebrates was considered to lack any mechanism of memory. However, the study of their response has shown a kind of acquired immunity, which is not so well understood given the lack of knowledge of the invertebrate defense system. This event can be called "innate immune memory." Recent studies using Biomphalaria glabrata snails have reported this phenomenon, relating it to an increase in humoral products, but no focus was given to hemocyte response or to other species of snails. In this study, we focus on hemocyte dynamics and some humoral factors in the species B. glabrata and B. straminea, the most widespread species in Brazil, sensitized and non-sensitized to the Schistosoma mansoni worm. We report a change in the prevalent hemocyte type after sensitization, through an increase in the proportion of granulocytes, as well as a change in the total number of hemocytes caused by a second exposure to the parasite. We also showed that melanization is not a key factor in Biomphalaria snail defense and varies little after the second exposure event. The data reported in this article confirm the effect of immune priming on these snails and suggest that the increase of humoral products shown in the literature is accompanied by variation in hemocytes after sensitization.