[Significance of schistosome lectins in the host allergic reaction evoked by penetration of cercaria].

Cercarial dermatitis is a skin allergic response caused by larval stages (cercariae) of the trematode family Schistosomatidae. In the Czech Republic the main causative agents of the disease are bird schistosomes of the genus Trichobilharzia. In the past it was supposed that cercariae of animal schistosomes die soon after the penetration into the human skin. However, we observed a migration and partial development of T. szidati cercariae within a nonspecific (mouse) host. The initial development of parasites in mice was similar to that observed in a specific host (duck) as well as to that described in human schistosomes causing schistosomiasis. After penetration, the transformation of T. szidati cercaria to schistosomulum is characterised by ultrastructural and biochemical changes, resulting in formation of a new parasite surface as well as in differences in specific binding of various lectins and host immunoglobulins to parasite surface components. It seems that the transformation of parasites represents a part of their immune evasion within the infected host. It was observed that T. szidati cercariae possess lectins localized on the parasite surface and in postacetabular penetration glands. It is supposed that, after the penetration into the skin, when glycocalyx disappears and gland material is expelled, the parasite surface may serve as an activator of the alternative complement pathway. The postacetabular gland components have probably a lytic function and facilitate migration of parasites through the skin. Moreover, the gland content is considered to play a role in shedding of surface antigens and in changes of parasite tegumental architecture.