The Association of High Prevalence of Trophozoites in Peripheral Blood with Lower Antibody Response toP. falciparumInfected Erythrocytes among Asymptomatic Children in Sudan

Abstract

Background. The most prominent variant surface antigens (VSAs) ofPlasmodium falciparumare the var gene-encodedPlasmodium falciparumerythrocyte membrane protein 1 (PfEMP1) family, which serves as a parasite-sequestering ligand to endothelial cells. In this study we have examined the antibody reactivity of autologous plasma from symptomatic and asymptomatic malaria infected children against the infected erythrocytes’ surface antigens using flow cytometry.Methods. Ethidium-bromide-labelled erythrocytic mature forms ofP. falciparumparasites obtained from symptomatic and asymptomatic children were sequentially incubated with autologous plasma and fluorescein isothiocyanate-conjugated (FITC) antihuman IgG. Plasma antibody reactivity was detected by flow cytometry.Results. Asymptomatic children had more prevalence of trophozoites in peripheral blood (66%) compared to symptomatic children (16%),p=0.002. The mean percentage of infected RBCs reacting with autologous sera was 89.78 among symptomatic children compared to 79.62 among asymptomatic children (p=0.09). Moreover, the mean fluorescence intensity (MFI) in the asymptomatic was significantly higher compared to symptomatic children (pvalue = 0.040).Conclusion. Variant surface antigens onPlasmodium falciparuminfected RBCs from symptomatic malaria children tend to be better recognized by IgG antibodies. This may suggest a role of some IgG antibodies in severity of malaria.