Naturally Acquired Antibody Responses to a Synthetic Malaria Antigen

Rebeka Nazareth, Pius Horumpende, Tolbert Sonda, Arnold Ndaro, Edson Mollel, Eliakim Paul, Emmanuel Athanase, Jaffu Chilongola
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Background: A major challenges to malaria vaccine development is identification of protective epitopes and understanding the nature and targets of protective immune responses.

Objective: To characterize naturally Immunoglobulin G (IgG) antibody responses to the synthetic peptide AS202.11, a malaria vaccine candidate molecule.

Methodology: This community based cross-sectional study enrolled 320 participants aged 1 year and above, residing in the study area. Demographic information of participants was recorded in a specially prepared questionnaire. Detection of P. falciparum infection was done by microscopy, malaria Rapid Diagnostic Test (mRDT) and confirmed by Polymerase Chain Reaction. Detection and quantification of IgG antibody was done using indirect ELISA. Data was analyzed by using STATA version 14.

Results: The overall AS202.11 IgG seropositivity was 78.8% (73.9 – 82.9). Seropositivity by age categories were: ≤12 years [74.3% (67.4 - 80.2)], 13-40 years [85.3% (76.5 – 91.1)] and >40 years [82.6% (68.7 – 91.1)]. In comparison with the ≤ 12 years group, adjusted ORs for the other age groups (95% CI) were 2.22 (1.14-4.32), p=0.019 and 1.87(0.81-4.35), p=0.143 for the 13-40 and >40 years groups of participants, respectively. The 13-40 years group had a statistically higher proportion of seropositive individuals compared to the ≤ 12 group. Seventy-eight (78.8%) of participants were seropositive for IgG antibodies to the AS202.11 peptide. Most infections (96.2%) were due to P. falciparum diagnosed by microscopy.

Conclusion: We report a high degree of recognition of the AS202.11 by IgG elicited by field P. falciparum strains, suggesting close similarity of the synthetic peptide to native P.falciparum antigens and possible suitability of the peptide as a future malaria vaccine candidate.