Potentiation of schistosome granuloma formation. By lentinan--a T-cell adjuvant

Abstract

Lentinan is a fungal polysaccharide which acts as a T-cell adjuvant. When this glucan was administered to thymus-intact mice by intraperitoneal injection, conspicuously enlarged lung granulomas formed in response to either Schistosoma mansoni or S japonicum eggs or to antigen-coated polyacrylamide beads. Liver granulomas in cercaria-induced S mansoni infection were augmented up to eight-fold in volume. By contrast, nude mice showed a complete absence of hypersensitivity granulomas, regardless of whether they received lentinan. Lentinan-potentiated granulomas show a distinctive histopathologic picture characterized by abundant, large, pale-staining macrophages; reduced and redistributed eosinophil populations; and frequent, extensive central necrosis, uncommon in unpotentiated schistosome foci. They also differ in their distributions of egg antigen and of host immunoglobulins. Optimal lentinan effects followed a single 1-mg dose when given to sensitized mice on the day of intravenous challenge with S mansoni eggs rather than at the time of intraperitoneal sensitization or following challenge. This adjuvant appears to act on effector T cells or on macrophages interacting with T cells; its effect on macrophages in a latex bead foreign body granuloma was minimal. A number of other lentinan-associated systemic effects on parasite and host were noted and described, including reduced female schistosome egg output.