Immunologic aspects of schistosomiasis.

Abstract

Immunity to schistosomes, helminth worms that infect 200 million people, is targeted to invading larvae (concomitant immunity). In vitro studies have revealed the role of T cells and of particular antibody isotypes in immune defense: IgE antibody cooperates with mononuclear phagocytes, eosinophils, and platelets to kill schistosome larvae. IgE antibody appears as an essential component of acquired resistance in rats. The role of IgE antibody has recently been confirmed by epidemiological studies demonstrating a positive correlation between the acquisition of resistance to reinfection by schistosomes and the level of IgE antibody to the parasite. A negative correlation found in these studies with the levels of IgM, IgG2, or IgG4 antibodies could be related to the development of a blocking antibody response. Antigens involved in protective immunity are expressed transiently at the surface of schistosomes. Sm28, a glutathione-S-transferase, induces significant protection against schistosome infection in rodents and nonhuman primates. In addition, this vaccine reduces the size of egg granulomas and egg output. Besides allowing the definition of a vaccine strategy against a major disease, studies on immunology of schistosomiasis have unraveled unsuspected antigenic mimicry between schistosomes and HIV regulatory proteins and have led to the demonstration that IgE antibody, a protective isotype against helminths, may also activate Fc epsilon-RII-bearing mononuclear phagocytes, eosinophils, and platelets in allergic disease.