Recent advances in immunity to human schistosomiasis

For many years the epidemiological significance of immunity in human schistosomiasis has been the subject of inconclusive debate. Recently, the results of studies from Brazil and Kenya, on Schistosoma mansoni and from Zimbabwe and The Gambia on S. haematobium have confirmed the importance of protective immunity. In communities in endemic areas the development of immunity to infection only occurs after many years of exposure. In part this is due to the slow development of antibodies which are protective but also to the earlier development of antibody isotypes which lack protective capacity and which are capable of interfering with the functioning of protective antibodies. Protective antibodies appear to be of the IgE class but some IgG subclasses may also be important. Initially, blocking antibodies were thought to be predominantly IgM and IgG2 but IgG4 also seems to possess blocking activity. The early production of blocking antibodies and late production of protective antibodies may be indicative of cytokine induced immunoglobulin class switching caused by the sequential involvement of different lymphokines.