Cellular immunity to merozoite surface protein 2 (FC27 and 3D7) in Papua New Guinean children. Temporal variation and relation to clinical and parasitological status.

A prospective study in 207 children aged 0.5-15 years was carried out in a highly endemic area of Papua New Guinea to examine the relationship between cellular responses to Plasmodium falciparum merozoite surface protein 2 (MSP2) and malaria infection and morbidity. In vitro proliferation, IFN-gamma and IL-4 induction were measured against two recombinant proteins of MSP2, FC27 and 3D7 as well as against a form of the 3D7 MSP2 lacking the central repetitive sequences (d3D7). The prevalence of proliferative response was generally low, 6% for FC27, 9% for 3D7 and 11% for d3D7. A higher prevalence of IL-4 response was obtained being 27% for FC27, 34% for 3D7 and 30% for d3D7 while the prevalence of IFN-gamma response was 13%, 15% and 18%, respectively. There was no correlation between age and proliferative responses; in contrast cytokine production increased with age for all three antigens. When proliferation or stimulation of either cytokine was used to assess T-cell activation the frequency of responders increased to 39%, 47% and 46% for FC27, 3D7 and d3D7 respectively. Analysis of the relation of T cell responses to concurrent infection and morbidity showed that lymphoproliferative response only to d3D7 was significantly associated with parasitaemia; while lymphoproliferative responses to all 3 MSP2 antigens were highest in the group of clinical malaria cases. There was no significant correlation between proliferation or cytokine production to MSP2 and concurrent or subsequent malaria morbidity.