Abstract
Schistosoma mansoni-infected individuals who have low intensities of reinfection following treatment produce immunoglobulin E (IgE) antibodies against a range of S. mansoni adult-worm antigens. One of the targets of the IgE response is an adult-worm sodium dodecyl sulfate-polyacrylamide gel electrophoresis band of 22 kDa (Sm22), which contains an antigen(s) located within the tegument and gut lining of adult worms and relatively late schistosomula life cycle stages only. A significant negative correlation between the level of anti-Sm22 IgE and the intensity of reinfection following treatment suggests that IgE responses against this antigen(s) are characteristic of individuals who are resistant to reinfection. To identify the antigen(s) in the Sm22 band that are associated with these IgE responses, we have cloned and characterized a recombinant 22-kDa protein (rSm22) that cross-reacts immunologically with Sm22. There was a high correlation between native and recombinant Sm22 isotype responses, indicating that the correct antigen had been cloned and that responses against rSm22 made up the majority of the responses against Sm22. By analyzing human isotype responses to rSm22 with human sera from a longitudinal treatment and reinfection study and correlating the anti-rSm22 isotype responses, retrospectively, with the intensity of reinfection following treatment for each individual, we observed a negative correlation between the IgE response to rSm22 and the intensity of reinfection. This relationship remained significant after allowing for age and other isotype responses to rSm22, in particular IgG4.