Determinants of Variant Surface Antigen Antibody Response in Severe Plasmodium falciparum Malaria in an Area of Low and Unstable Malaria Transmission

Genetic polymorphism of vir genes of Plasmodium vivax in Myanmar

The Plasmodium vivax variant proteins encoded by vir genes are highly polymorphic antigens and are considered as one of key proteins of P. vivax for host immune evasion via antigenic variations. Because genetic diversity of these antigens is a critical hurdle in the development of an effective vaccine, understanding the genetic nature of the vir genes in natural population is important. In this study, we selected four vir genes (vir 4, vir 12, vir 21, and vir 27) previously used for genetic analysis in several studies and evaluated the genetic polymorphisms and phylogenetic relationship of these 4 vir genes in Myanmar P. vivax population. Taken all genetic diversity values, the vir 12 (S = 168, H = 17, Hd = 0.854, Tajima's D value = 2.91524) was the most genetically diverse gene and the vir 4 (S = 9, H = 4, Hd = 0.744, Tajima's D value = -0.49151) was the most conserved gene. All phylogenetic trees showed two clades, and vir 4 and 12 haplotypes from Myanmar were clustered in a distinct clade with those from India and Republic of Korea. These results confirmed the pattern of high genetic polymorphism of vir genes and provided information on vir gene for further functional research and studies focused toward the practical use of vir genes.

Diversity of vir Genes in Plasmodium vivax from Endemic Regions in the Republic of Korea: an Initial Evaluation

Variant surface antigens (VSAs) encoded by pir families are considered to be the key proteins used by many Plasmodium spp. to escape the host immune system by antigenic variation. This attribute of VSAs is a critical issue in the development of a novel vaccine. In this regard, a population genetic study of vir genes from Plasmodium vivax was performed in the Republic of Korea (ROK). Eighty-five venous blood samples and 4 of the vir genes, namely vir 27, vir 21, vir 12, and vir 4, were selected for study. The number of segregating sites (S), number of haplotypes (H), haplotype diversity (Hd), DNA diversity (π and Θ_w), and Tajima’s D test value were conducted. Phylogenetic trees of each gene were constructed. The vir 21 (S=143, H=22, Hd=0.827) was the most genetically diverse gene, and the vir 4 (S=6, H=4, Hd=0.556) was the opposite one. Tajima’s D values for vir 27 (1.08530, P>0.1), vir 12 (2.89007, P<0.01), and vir 21 (0.40782, P>0.1) were positive, and that of vir 4 (−1.32162, P>0.1) was negative. All phylogenetic trees showed 2 clades with no particular branching according to the geographical differences and cluster. This study is the first survey on the vir genes in ROK, providing information on the genetic level. The sample sequences from vir 4 showed a clear difference to the Sal-1 reference gene sequence, whereas they were very similar to those from Indian isolates.

Plasmodium falciparum parasites causing cerebral malaria share variant surface antigens, but are they specific?

Background

Variant surface antigens (VSA) expressed on the surface of Plasmodium falciparum-infected red blood cells constitute a key for parasite sequestration and immune evasion. In distinct malaria pathologies, such as placental malaria, specific antibody response against VSA provides protection. This study investigated the antibody response specifically directed against VSA expressed by parasites isolated from individuals presenting a given type of clinical presentation.

Methods

Plasma and isolates were obtained from four groups of Beninese subjects: healthy adults, patients presenting uncomplicated malaria (UM), cerebral malaria (CM), or pregnancy-associated malaria (PAM). The reactivity of plasma samples from each clinical group was measured by flow cytometry against parasites isolated from individuals from each clinical group.

Results

Antibody responses against VSA_UM were predominant in CM, UM and HA plasmas. When analysed according to age in all plasma groups, anti-VSA_CM and -VSA_UM antibody levels were similar until six years of age. In older groups (6-18 and >19 years of age), VSA_UM antibody levels were higher than VSA_CM antibody levels (P = .01, P = .0008, respectively). Mean MFI values, measured in all plasmas groups except the PAM plasmas, remained low for anti-VSA_PAM antibodies and did not vary with age. One month after infection the level of anti-VSA antibodies able to recognize heterologous VSA_CM variants was increased in CM patients. In UM patients, antibody levels directed against heterologous VSA_UM were similar, both during the infection and one month later.

Conclusions

In conclusion, this study suggests the existence of serologically distinct VSA_CM and VSA_UM. CM isolates were shown to share common epitopes. Specific antibody response to VSA_UM was predominant, suggesting a relative low diversity of VSA_UM in the study area.

The profile of IgG-antibody response against merozoite surface proteins 1 and 2 in severe Plasmodium falciparum malaria in Eastern Sudan

In this study, antibodies (Ab) directed against three MSP antigens; MSP1(19), MSP2(A), and MSP2(B) were analyzed in blood samples obtained from 223 Sudanese patients who presented with either severe malaria (SM) or uncomplicated malaria (UM) and from 117 malaria-free donors (MF). The results showed that the prevalence of MSP Abs was associated with the clinical outcome of malaria infection, and the Ab prevalence was age-dependent (P<0.0005). More importantly, the prevalence of MSP Abs against the test antigens was lower in SM compared to UM (P=0.001 to 0.020), suggesting a protective role for these Abs against SM. Furthermore, the Ab responses between individual complications of SM were significantly different.