THE INFLUENCE OF MALOPRIM CHEMOPROPHYLAXIS ON CELLULAR AND HUMORAL IMMUNE-RESPONSES TO PLASMODIUM-FALCIPARUM ASEXUAL BLOOD-STAGE ANTIGENS IN SCHOOLCHILDREN LIVING IN A MALARIA ENDEMIC AREA OF MOZAMBIQUE

We examined the impact of chemoprophylaxis on the cellular and humoral immune responses to polypeptides of the asexual Plasmodium falciparum blood stage antigens, the glutamate rich protein GLURP and Pf155/RESA , both of which in previous field studies have been identified as pote ntially protective antigens. The study was carried out in the Escola P rimaria de Lingamo, a primary school in a suburban area of Maputo, Moz ambique. A cohort of 392 schoolchildren (aged 7-12 years) was randomly allocated to two equal groups, one receiving chemoprophylaxis with da psone/pyrimethamine (Maloprim), the other receiving placebo every week from December 1989 to November 1990. The groups were then followed un til November 1991 without chemoprophylaxis. Cellular responses to immu nodominant epitopes from Pf155/RESA and GLURP, and to non malaria anti gens C. albicans and PPD, were assessed by lymphocyte proliferation as says in vitro. Anti-GLURP and anti-Pf155/RESA antibodies were detected by enzyme-linked immunosorbent assay(ELISA) and erythrocyte membrane immunofluorescence (EMIF), and total anti-P. falciparum antibodies wer e measured by indirect fluorescent antibody test (IFAT). Immunological reactivities were evaluated every six months, at the end of the rainy season and at the end of the dry season, both during the period of ch emoprophylaxis and during the follow-up. The antibody response rate to the GLURP was lower in the Maloprim group than in the placebo group d uring the intervention phase. The lymphoproliferative response rate to the malaria antigens was significantly lower at the end of the rainy season than at the end of the dry season, but the difference between t he experimental group and the control group of schoolchildren was not statistically significant. These results suggest that the antibody res ponses to the GLURP molecule and partly to the Pf155/RESA antigen in t his study population were shortlived and dependent on frequent booster ing, but whether these antigens play a role in the development of natu ral clinical immunity remains open. In the experimental group of schoo lchildren weekly chemoprophylaxis successfully reduced the parasite ra te during the rainy season from 43% to 4%, and during the dry season f rom 18% to O%. Chemoprophylaxis may therefore have a useful role in co mbination with another partially effective malaria control measure suc h as insecticide-impregnated bed nets or a malaria vaccine.