IgM antibody responses to the circumsporozoite protein in naturally acquired falciparum malaria

Abstract

The circumsporozoite (CS) protein on the surface of sporozoites is the major target for antibody response(s) to the infective stage of the malaria parasite. Sera from malaria endemic areas contain both IgM and IgG antibodies that react with a dominant epitope in the tetrapeptide repeat region of the CS protein. In order to characterize the IgM CS antibody response in Plasmodium falciparum (PF) malaria, a prospective study was conducted in Thai Rangers. Variable IgM responses against the CS protein were detected in 81% of 47 PF-infected subjects. Similar to IgG response kinetics, IgM levels rose to a peak 6-10 days after detection of parasitemia and showed an apparent serum half-life of less than 25 days. The classic difference in isotype ratio (IgG/IgM) between primary and secondary antibody responses was observed to blood-stage, but not CS, antigens.

Antibody responses to Plasmodium falciparum: evolution according to the severity of a prior clinical episode and association with subsequent reinfection.

“…Non-responsiveness to circumsporozoite protein in a proportion of individuals living in endemic areas is a well-documented finding. 5,10,14,15,30,32,33 Our findings both confirm and extend these observations, showing that the lack of an anti-NANP IgG response persists over time in some individuals despite the fact that they are all able to produce IgM to the same molecule. In addition, more than 50% of these nonresponsive individuals were reinfected at least once prior to collection of the last plasma sample.…”