The surface-associated
glycopeptides gp40, one of the most polymorphic Cryptosporidium
antigens, and gp15, one of the most immunodominant Cryptosporidium
antigens, are putative
vaccine candidates because they mediate
infection in vitro and induce immune responses in vivo. We evaluated antibody responses to these
antigens before and after the first episode of symptomatic
cryptosporidiosis in 51 children from a birth cohort study in an area in South India where Cryptosporidium is endemic and a major cause of parasitic
diarrhea.
IgG levels to gp15 and to homotypic and heterotypic gp40
antigens were measured in pre- and postdiarrheal sera by
enzyme-linked
immunosorbent assay (ELISA). There was a significant
IgG response to gp15 (P < 0.001) following the first episode of cryptosporidial
diarrhea. Using a general additive model, we determined the estimated time of the peak
IgG response to gp15 to be 9.3 weeks (confidence interval, 5.2 to 13.4) following the diarrheal episode. In a subset of 30 children infected with Cryptosporidium hominis subtype Ia, there was a significant difference in
IgG responses to homotypic C. hominis Ia and to heterotypic Cryptosporidium parvum II gp40
antigens (P = 0.035). However, there was also a significant correlation (P = 0.001) in the responses to both
antigens in individual children, suggesting that while responses are in part subtype specific, there is significant cross-reactivity to both
antigens. This is the first report of the characterization of immune responses to
cryptosporidiosis in Indian children and the first study to investigate human immune responses to the polymorphic gp40
antigen. However, further studies are needed to determine whether immune responses to these
antigens are protective against subsequent
infections.