Abstract. Cellular and humoral immune responses to Schistosoma mansoni antigen preparations were evaluated in individuals presumed to be susceptible or resistant to reinfection after chemotherapeutic cure. A consistent proliferative increase in the response to soluble egg antigen (SEA) was observed post-treatment in both the susceptible and resistant groups. However, this change was not related to resistance. Isotype studies showed that IgM antibody levels to soluble worm antigen preparation (SWAP) and cercariae antigens were significantly higher in the resistant group than in the susceptible group. Post-treatment, an increase in IgE anti-SWAP and anti-schistosomular tegument (STEG) responses and a decrease in IgG4 anti-SEA and anti-STEG responses were observed in the resistant group. These finding are similar to those we have reported previously for a putative resistant group termed endemic normals, and are compatible with immunologic studies in different endemic areas. Together, these findings indicate that even on the population level, high IgE specificities coupled with low IgG4 specificities correlate well with documented resistance to reinfection.Based on field studies following curative chemotherapy of either Schistosoma mansoni 1-3 or S. haematobium, 4,5 individuals are often categorized as being either susceptible or resistant to natural reinfection by schistosomes. These studies have shown that resistance to reinfection is an age-related phenomenon, with most people in endemic areas becoming resistant, or expressing their resistance during their second decade of life. When determined directly or by estimation, resistance appears to be unrelated to the degree of contact that the susceptible and resistant groups have with cercariaecontaining water, and is usually attributed to immunity rather than physiologic or behavioral changes with age. 4,6,7 These studies have cataloged a variety of humoral immune responses, and are in agreement with several of the correlations demonstrated between given immune responses and susceptible or resistant groups. 8,9 A number of studies have shown associations between resistance status and a balance between the level of effective anti-schistosomula antibodies and the presence of blocking antibodies. 5,[10][11][12] The latter are sometimes most easily demonstrated as antibodies to egg antigens that cross-react with epitopes present in the schistosomula tegument.
3,10The most common features that show relationships to resistance to reinfection include high levels of IgE against adult worm or larval antigens, while high levels of IgG4 and IgM antibodies against egg antigens generally parallel susceptibility. 5,9,[11][12][13][14][15] Recent studies have also reported correlations between resistance and elevated levels of IgA against a schistosome vaccine candidate (Sm 28 glutathione-S-transferase). 16,17 Further studies with other antigens have demonstrated that higher levels of IgE against a 22-kD schistosomula moiety 9 and higher levels of IgM against a 68-kD adult schistos...