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There are emerging reports of poor efficacy of artemisinin-based combination treatment (ACT). However, mutations on the Kelch-13 gene marking delayed parasite clearance have no clinically defined relationship yet with ACT resistance across Africa. With improved malaria control efforts, declining acquired immunity could be responsible for varying drug response profiles that may be dependent on levels of exposure to infections. To examine the influence of antibody response on parasite clearance rate during treatment with artemether-lumefantrine (AL), plasma samples were collected, prior to treatment, from individuals presenting with
uncomplicated malaria. Five hundred and sixty-one individuals were screened, of which 26.7% (150) tested positive for P. falciparum. One hundred and twelve participants (43.3%) (65, male: 18, female: 47) of the P. falciparum positive patients met the inclusion criteria and were enrolled, treated with AL (Coartem) and followed up for 28 days. The participants were
categorized into three age groups: 1–5years (12 individuals; 18.5%); 6–14 years (19 individuals; 29.2%) and ≥15 years old (34 individuals; 52.3%). Using varATS qPCR, two main parasite clearance profiles of the participants were described. Individuals with parasite clearance within 24 hours (early group, N=20) and the others with clearance between 48–72 hours (late group, N =39). Magnetic bead-based luminex assay was used to profile antibody responses specific to a panel of 21 Plasmodium falciparum sporozoite, merozoite and An. gambiae salivary antigens. Median fluorescence intensity (MFI) of the antibodies was highest
against glutamate-rich protein (GLURP) and lowest against merozoite surface protein (MSP2)antigen. Anti-Rh2030, EBA175, HSP40, CSP, MSP2.Ch150, Rh42, MSP2, Hyp2, GLURP, H103, AMA1, SEA, GexP, Etramp4.Ag2, MSP1.19, and EBA140 level antibody levels were higher in older individuals compared with younger individuals. While anti-gsG6 and Rh5 were
higher in younger individuals. GST, MSP2, and SBP1 had no significant difference (p>0.05) in both young and old individuals. High levels of antibodies against almost all the antigens in individuals with late parasite clearance were higher when compared with the individuals with fast parasite clearance rate except EBA175, EBA140, MSP1.19, CSP, RH4.2, and GLURP.
Characterization of additional markers in larger populations is required to reveal potential immunological correlates of drug efficacy, potential vaccine candidates and immune boosters.Keywords: Artemisinin-based combination treatment, Immunity, Antibody, Artemetherlumefantrine, varATS, Luminex