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Fulltext Induction and Kinetics of Complement-Fixing Antibodies Against Plasmodium vivax Merozoite Surface Protein 3α and Relationship With Immunoglobulin G Subclasses and Immunoglobulin M

Oyong DA, Wilson DW, Barber BE, William T, Jiang J, Galinski MR, et al.

J Infect Dis, 2019 11 06;220(12):1950-1961.
PMID: 31419296 DOI: 10.1093/infdis/jiz407

BACKGROUND: Complement-fixing antibodies are important mediators of protection against Plasmodium falciparum malaria. However, complement-fixing antibodies remain uncharacterized for Plasmodium vivax malaria. P. vivax merozoite surface protein 3α (PvMSP3α) is a target of acquired immunity and a potential vaccine candidate.
METHODS: Plasma from children and adults with P. vivax malaria in Sabah, Malaysia, were collected during acute infection, 7 and 28 days after drug treatment. Complement-fixing antibodies and immunoglobulin M and G (IgM and IgG), targeting 3 distinctive regions of PvMSP3α, were measured by means of enzyme-linked immunosorbent assay.
RESULTS: The seroprevalence of complement-fixing antibodies was highest against the PvMSP3α central region (77.6%). IgG1, IgG3, and IgM were significantly correlated with C1q fixation, and both purified IgG and IgM were capable of mediating C1q fixation to PvMSP3α. Complement-fixing antibody levels were similar between age groups, but IgM was predominant in children and IgG3 more prevalent in adults. Levels of functional antibodies increased after acute infection through 7 days after treatment but rapidly waned by day 28.
CONCLUSION: Our study demonstrates that PvMSP3α antibodies acquired during P. vivax infection can mediate complement fixation and shows the important influence of age in shaping these specific antibody responses. Further studies are warranted to understand the role of these functional antibodies in protective immunity against P. vivax malaria.
Fulltext IgM in human immunity to Plasmodium falciparum malaria

Boyle MJ, Chan JA, Handayuni I, Reiling L, Feng G, Hilton A, et al.

Sci Adv, 2019 09;5(9):eaax4489.
PMID: 31579826 DOI: 10.1126/sciadv.aax4489

Most studies on human immunity to malaria have focused on the roles of immunoglobulin G (IgG), whereas the roles of IgM remain undefined. Analyzing multiple human cohorts to assess the dynamics of malaria-specific IgM during experimentally induced and naturally acquired malaria, we identified IgM activity against blood-stage parasites. We found that merozoite-specific IgM appears rapidly in Plasmodium falciparum infection and is prominent during malaria in children and adults with lifetime exposure, together with IgG. Unexpectedly, IgM persisted for extended periods of time; we found no difference in decay of merozoite-specific IgM over time compared to that of IgG. IgM blocked merozoite invasion of red blood cells in a complement-dependent manner. IgM was also associated with significantly reduced risk of clinical malaria in a longitudinal cohort of children. These findings suggest that merozoite-specific IgM is an important functional and long-lived antibody response targeting blood-stage malaria parasites that contributes to malaria immunity.

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