Antibody responses in Burkinabe children against P. falciparum proteins associated with reduced risk of clinical malaria

Abstract

Individuals residing in malaria-endemic regions with high disease transmission can develop semi-immunity within five years of age. Although understanding the target of the IgGs in this age group helps discover novel blood-stage vaccine candidates and serological markers, it has not been well elucidated due to limited accessibility to plasmodial antigens and samples. This study presents the first comprehensive analysis of antibody levels in plasma obtained from Burkinabe children (n=80, aged 0 to 5 years) to 1307 Plasmodium falciparum proteins expressed by the eukaryotic wheat germ cell-free system. Antibody levels were measured by AlphaScreen. We found that 98% of antigens were immunoreactive. The number of reactive antigens by the individual was correlated with increasing age. The most significant increases in seroprevalence occur during the first 2 years of life. By correlating antibody levels and the number of clinical malaria during a 1-year follow-up period, we identified 173 potential protein targets which might be associated with clinical immunity. These results provide valuable insights into how children acquired semi-immunity to malaria in their early lives.

Keywords: AlphaScreen; Burkinabe children; Plasmodium falciparum; blood-stage; immune response; immunoglobulin G; serology; wheat germ cell-free system.

Figure 1

(A) Seroprevalence of each age group (0-0.5, >0.5-1, >1-2, >2-3, >3-4, >4-5, and all). Box plots illustrated the median and the 25/75 percentiles, with whiskers extending to 1.5 times the interquartile range. Dashed blue lines indicate the cut-off value of 10% seroprevalence. The differences among age groups were analyzed by the Wilcoxon rank sum test with Bonferroni correction: ***P<0.001, NS, not significant. (B) The relationship between age and the number of episodes per period of malaria risk (RpT). A significant negative correlation between age and RpT for 79 individual plasma samples (one plasma from a 0-0.5 group infant with RpT=0 was excluded) was observed using Spearman’s rank correlation, rho = - 0.514, P = 1.236×10^-6. The lines were drawn by using linear regression.

Figure 2

The antibody responses of the top 10 antigens associated with reduced risk of clinical malaria episodes. (A) The scatter plots of the ASC (normalized, log-transformed and backgound-subtracted AlphaScreen Count) and RpT (the number of episodes per period of malaria risk) with P-value and rho derived from Spearman’s rank correlation. The straight lines were drawn by linear regression. (B) The seroprevalence of different age groups. (C) The comparison of log-transformed ASC between the 0-0.5 and >0.5-1 age groups. The bar and error bar indicate the mean and the standard error, respectively. No significant differences were observed by Welch’s t-test.