Understanding the role of adaptive immunity in a protective yet infection permissive immune response to the Cryptosporidium parasite

Background: Cryptosporidium is one of the top causes of diarrhea in Bangladesh infants. Cryptosporidium infections lead to the production of antibody immune responses, which were associated with a decrease in parasite burden and decreased disease severity in subsequent infections. Methods: We conducted a longitudinal study of cryptosporidiosis from birth to five years of age in an urban slum of Dhaka Bangladesh. We then retrospectively tested all available samples from the stool collected during 0-3 years from 54 children by enzyme-linked immunosorbent assay (ELISA). We also assessed the concentration of anti-Cryptosporidium Cp17 or Cp23 IgA and IgG antibodies in the childrens plasma (1- 5 years). Results: The seroprevalence of both anti- Cp23 and Cp17 antibodies was high at greater than one year of age and reflected the exposure of these children in this community to cryptosporidiosis. Elevated levels of the antibodies against the antigens were associated with protection from reinfection but gradually decreased over the study period. In Bangladesh, the prevalence of cryptosporidiosis is high during the rainy season (June to October) but decreases during the dry season. Fecal anti-Cp23 and anti-Cp17 levels were unchanged irrespective of seasonality however in younger infants plasma anti-Cp17 and Cp23 IgG and anti-Cp17 IgA levels were markedly higher during the rainy season. Conclusions: In Bangladeshi children, infection resulted in anti-Cp23 and anti-Cp17 IgA and IgG antibodies. independent of the number of subsequent Cryptosporidium reinfections. This was associated with a decrease in both the number of reinfections and the amount of oocyst shed in child feces.