The solid-phase enzyme-linked immunospot assay has been adapted for enumerating cells secreting antibodies to crude antigenic extracts from the main developmental stages of Schistosoma mansoni. The frequencies of splenocytes secreting antibodies reactive with soluble antigenic extracts from cercariae, adult worms, and eggs, were examined in C57BL/6 mice during the first 12 weeks of a primary infection with S. mansoni. Despite the existence of cross-reactive moieties present in these antigenic preparations, the characteristics of the responses monitored differed with regard to kinetics, magnitude, and/or isotype distribution. The responses peaked between 8 and 10 weeks of infection, were characterized by a predominance of cells secreting IgM antibodies against all three antigens, and followed the patterns IgM > IgA > IgG for cercariae, IgM > IgG IgA for adult worms and IgM > IgG > IgA for egg extracts. On the other hand, these patterns were not always reflected in serum, expecially for cercariae-reactive circulating IgG and IgA responses. When examined for numbers of total IgM-, IgG- and IgA-producing cells, the spleen of 5. mαnsom-infected mice was shown to display considerable numbers of immunoglobulin-producing cells in all three isotypes studied. The most spectacular increases were noted for IgG-secreting cells (more than 10-fold) and for IgM-secreting cells (up to 6-fold) 4 weeks after initial cercarial exposure. Taken together, these observations indicate that primary infection with S. mansoni results in early immunoregulatory alterations which may contribute to the maintenance of specific as well as nonspecific B cell hyperactivity. The data presented in this study also suggest that the solid-phase enzyme-linked immunospot assay may have informative value in documenting the dynamic and anatomical aspects of such alterations in a variety of other tissues draining the sites of parasite migration
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