Association between Immunoglobulin G Subtypes Immune responses to Plasmodium falciparum Merozoite Surface Protein 1-19 and Malaria

Aims: To determine Immunoglobulin G (IgG) subtypes (IgG1, IgG2, IgG3 and IgG4) responses to
PfMSP1-19 antigens and their associations with malaria across different age groups.
Study Design: A community based cross sectional study.
Place and Duration of Study: Bondo Ward, in Handeni district of Tanga Region between January
and May 2016.
Methodology: We included 331 participants; 216 females, 115 males aged between 1 and 82 years,
with a median age of 10 years and an inter-quartile range 5 -30 years. Two milliliters of blood was
collected from each participant in EDTA coated tubes for detection of malaria and serology. Anti-
MSP1-19 IgG subtypes were measured by indirect ELISA based on a protocol developed by Afro
Immuno-Assay Consortium. Demographic data were collected using designed record form.
Results: Out of 331 participants, 68 (20.5%) were malaria positive. We report malaria prevalence to
be highest in the age category of between 6 and 15 years, compared to individuals above 15 years
(OR= 4.5; 95% CI = 2.2–8.9). Most participants were seropositive for total IgG (87.0%), IgG1 (78.5%)
and IgG3 (52.9%). Concentration (optical densities) of total IgG, IgG1 and IgG3 was generally lower in
the 1-5 year age category. There was no clear pattern for IgG 2 and IgG4 seropositivity across age
categories. After adjusting for age, only IgG1 seropositivity was significantly associated with lower
malaria prevalence in all age categories (OR=0.4; 95% CI = 0.2 – 0.8).
Conclusion: IgG1subtype to MSP1-19 is associated with lower malaria prevalence which may imply its
possible suitability a target of a prospective malaria vaccine. We report a high prevalence of malaria
in the study area, with highest malaria prevalence recorded in older children of 6-15 years of age. Our
findings show that only IgG1 antibody to MSP1-19 is associated with low malaria prevalence,
suggesting a possible protective role of the subtype against malaria. We report very low responses
and seropositivity of IgG2 and IgG4 subtypes. Based on our present findings, IgG1 to MSP1-19 could
be an important target of a prospective malaria vaccine.