Antibody Responses Against Plasmodium vivax TRAP Recombinant and Synthetic Antigens in Naturally Exposed Individuals From the Brazilian Amazon

Abstract

Thrombospondin-related adhesive protein (TRAP) is essential for sporozoite motility and the invasion of mosquitoes' salivary gland and vertebrate's hepatocyte and is, thus, considered a promising pre-erythrocytic vaccine candidate. Despite the existence of a few reports on naturally acquired immune response against Plasmodium vivax TRAP (PvTRAP), it has never been explored so far in the Amazon region, so results are conflicting. Here, we characterized the (IgG and IgG subclass) antibody reactivity against recombinant PvTRAP in a cross-sectional study of 299 individuals exposed to malaria infection in three municipalities (Cruzeiro do Sul, Mâncio Lima and Guajará) from the Acre state of the Brazilian Amazon. In addition, the full PvTRAP sequence was screened for B-cell epitopes using in silico and in vitro approaches. Firstly, we confirmed that PvTRAP is naturally immunogenic in the cohort population since 49% of the individuals were IgG-responders to it. The observed immune responses were mainly driven by cytophilic IgG1 over all other sublcasses and the IgG levels that was corelated with age and time of residence in the studied area (p < 0.05). Interestingly, only the levels of specific anti-TRAP IgG3 seemed to be associated with protection, as IgG3 responders presented a significantly higher time elapse since the last malaria episode than those recorded for IgG3 non-responders. Regarding the B-cell epitope mapping, among the 148 responders to PvTRAP, four predicted epitopes were confirmed by recognition of antibodies (PvTRAPR197−H227; PvTRAPE237−T258; PvTRAPP344−G374; and PvTRAPE439−K454). Nevertheless, the frequency of responders against these peptides were low and did not show a clear correlation with the antibody response against the corresponding antigen. Moreover, none of the linear confirmed epitopes were located in the binding regions of PvTRAP in respect to the host cell ligand. Collectively, our data confirm the PvTRAP immunogenicity among Amazon inhabitants, while suggesting that the main important B-cell epitopes are not linear.

Recombinant Plasmodium vivax circumsporozoite surface protein allelic variants: antibody recognition by individuals from three communities in the Brazilian Amazon

“…Anti-PvCSP specific antibodies against recombinant VK210, VK247, Vivax-like and C terminal region (CT), were evaluated by enzyme-linked immunosorbent assay (ELISA) as previously described by Matos et al 48 . Briefly, MaxiSorp 96-well plates (Nunc, Rochester, NY, USA) were coated overnight with 1.0 µg/ml of each recombinant protein.…”

Analysis of Pre-Erythrocytic Immunity During Plasmodium Vivax Infection Reveals a Diversity of Responses That is Partially Due to Blood Stage Cross-Reactivity

“…A P. vivax cohort study in a low-transmission P. vivax area in western Thailand during 2013 showed prevalence of 86%, 21% and 0% for CSP, CELTOS and TRAP antigens, respectively [28]. However, a crosssectional study of naturally acquired immunity performed in Brazil during 2016 against whole and synthetic peptides of PE TRAP showed prevalence of 46% and 25-32%, respectively [29]. Our results showed naturally acquired immunity against all 12 PE antigens tested in P. vivax patients with generally higher proportions of individuals responding to all PE antigens (range of 58-99%).…”

Changes in B Cell Pool of Patients With Multibacillary Leprosy: Diminished Memory B Cell and Enhanced Mature B in Peripheral Blood

“…The IgG level in each sample was calculated interpolating the mean optical density value of the sample on a linear regression graphic of recombinant IgG (ref. 15260) standard curve dilution (ranging from 0.500 to 0.031 µg/mL) performed using the same conditions described above ( 27 ).…”