Longitudinal study of natural immune responses to the Plasmodium falciparum apical membrane antigen (AMA-1) in a holoendemic region of malaria in western Kenya: Asembo Bay cohort project VIII

We investigated the development and maintenance of proliferative and antibo dy responses to apical membrane antigen-1 (AMA-1) epitopes in a holoendemic area of western Kenya. Young children (< 10 years), older children (10-17 years), and adults ( greater than or equal to 18 years) were followed longi tudinally for antibody and T-cell responses at 3 time points with an interv al of 3-4 months. The proliferative responses against the AMA-I T epitopes (PL171, PL172, PL173, PL186, PL191, and PL192) were not stable during follo w-up; however, response to mycobacterial antigen PPD was highly stable. The responder frequencies were similar in all 3 time points except for epitope PL192. The younger and older children responded more frequently to T-cell epitopes, but the differences were not significant. A positive proliferativ e response to PL191 was associated with a significantly lower risk of paras itemia at subsequent follow-up (relative risk, 0.5; P = 0.03). The presence of antibody response to B epitopes PL169, PL170, PL173, PL187, and PL192 i n one time point was associated with a subsequent response (P = 0.0001-0.00 8) suggesting a stable response. Younger (P = 0.046) and older children (P = 0.017) more frequently responded to epitope PL169 than did adults, and ad ults responded more frequently to PL187 than did younger children (P = 0.00 9). Responses to AMA-1 T-cell epitopes were short lived, and antibody respo nses were relatively stable.