A comparative study of natural immune responses against Plasmodium vivax C-terminal merozoite surface protein-1 (PvMSP-1) and apical membrane antigen-1 (PvAMA-1) in two endemic settings

Abstract

The mechanisms of cellular and humoral immune responses against P. vivax parasite remain poorly understood. Several malaria immunological studies have been conducted in endemic regions where both P. falciparum and P. vivax parasites co-exist. In this study, a comparative analysis of immunity to Plasmodium vivax antigens in different geography and incidence of Plasmodium spp. infection was performed. We characterised antibodies against two P. vivax antigens, PvMSP-1 and PvAMA-1, and the cross-reactivity between these antigens using plasma from acute malaria infected patients living in the central region of China and in the western border of Thailand. P. vivax endemicity is found in central China whereas both P. vivax and P. falciparum are endemic in Thailand. There was an increased level of anti-PvMSP-1/anti-PvAMA-1 in both populations. An elevated level of antibodies to total P. vivax proteins and low level of antibodies to total P. falciparum proteins was found in acute P. vivax infected Chinese, suggesting antibody cross-reactivity between the two species. P. vivax infected Thai patients had both anti-P. vivax and anti-P. falciparum antibodies as expected since both species are present in Thailand. More information on humoral and cell mediated immunity during acute P. vivax-infection in the area where only single P. vivax species existed is of great interest in the relation of building up anti-disease severity caused by P. falciparum. This knowledge will support vaccine development in the future.

Keywords: Plasmodium falciparum; Plasmodium vivax; antibody to malaria; malaria immunity.

Table 1. Information and clinical data of P. vivax patients, immune and naïve controls

Table 2. PCR primers and sequences

Figure 1. Absorbance (405 nm) value of IgG antibody reacting with (A) crude P. vivax antigens, (B) recombinant P. vivax MSP-1₁₉ protein, (C) recombinant P. vivax AMA-1 protein, and (D) crude P. falciparum antigen respectively, in the naïve controls (NC), immune controls (IC), acute P. vivax infection (AC) comparing between Chinese and Thai patients. Data are shown in median, interquartile ranges (box plots), maximum and minimum (upper-lower lines).