Effects of Trichobilharzia ocellata on hemocytes of Lymnaea stagnalis

Abstract We analyzed the effects of infection with Trichobilharzia ocellata on hemocytes of its snail host, Lymnaea stagnalis , and correlated them with successive stages of parasite development. Circulating hemocytes were studied at 0, 2, 4, 6, and 8 weeks post exposure (p.e.) with respect to cell number, distribution of subpopulations (as characterized by morphology, determinants recognized by either of two lectins and a monoclonal antibody) and to proliferative, phagocytic and endogenous peroxidase activity. Infection results in a net elevated level of activity of circulating hemocytes at 2 weeks p.e., when mother sporocysts are present in the head-foot-mantle region, as well as at 4 weeks p.e., when daughter sporocysts are migrating to and growing in the digestive gland region. A lower level of activity was observed at 6 weeks p.e., when cercariae are differentiating within daughter sporocysts. A net activation was again found at 8 weeks p.e., when cercariae are escaping. So, infection with T. ocellata results in a net general activation of the internal defense system of L. stagnalis , during several stages of development of the parasite.