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Summary: Dr. Haque is studying the mechanisms of acquired immunity to E. histolytica infection and disease in Bangladeshi children.

It was not known whether acquired immunity to Entamoeba histolytica infection exists. Many prior studies are impossible to interpret because E. histolytica–specific tests were not used. We are conducting a prospective cohort study in children in Mirpur, Dhaka, Bangladesh. In this study, we found that acquired immunity to E. histolytica infection was linked to intestinal IgA against the CRD of the Gal/GalNAc lectin of E. histolytica, and resistance to infection was seen despite the fact that children were infected with genetically diverse strains of E. histolytica. We are continuing to follow the children of this cohort to better understand the immunity to E. histolytica infection and disease. We have studied the duration of immunity as documented by the stool anti-CRD IgA response and natural E. histolytica infection and on the role of MHC class II alleles in protection against E. histolytica infection.

During the four-year period follow-up, 80 percent (162/202) of the children had a total of 384 episodes of new asymptomatic E. histolytica infection, 20 percent (40/202) experienced E. histolytica–associated diarrhea, and 12 percent (24/202) had E. histolytica-associated dysentery. The duration of protection conferred by a positive stool anti-CRD and natural E. histolytica infection was measured using the Kaplan-Meier survival analysis. The median duration of protection after a positive stool anti-CRD IgA response was 744 days (95 percent CI, 586–902 days). The median duration of protection after the first E. histolytica infection was 616 days (95 percent CI, 490–741 days). We have also identified a potential protective association with the class II allele DQB1*601 and the DQB1*601-DRB1*1501 haplotype with E. histolytica infection among this cohort of children. Our results suggest that, along with mucosal anti-CRD IgA antibodies, human genes underlie susceptibility to intestinal infection with E. histolytica. The study has several implications for vaccine development to prevent amebic disease and infection.