Differential induction of immunoglobulin G to Plasmodium falciparum variant surface antigens during the transmission season in Daraweesh, Sudan

BACKGROUND: The acquisition of immunoglobulin (Ig) G to variant surface antigens (VSAs) seems important for the development of protective immunity against malaria. Unlike VSAs expressed by parasite isolates associated with uncomplicated malaria, VSAs expressed by parasite isolates associated with severe malaria (VSA(SM)) are frequently recognized by IgG.

METHODS: We analyzed levels of anti-VSA IgG in 57 individuals in Daraweesh, Sudan, before and after the transmission season. IgG responses to 79 Plasmodium falciparum isolates from children with defined malaria syndromes and exposed to high transmission in a different part of Africa were also analyzed.

RESULTS: After the transmission season, individuals with malaria had an increase in IgG recognition to 25.8% (95% confidence interval [CI], 19.9%-31.7%) and a decrease in IgG recognition to 7.6% (95% CI, 4.4%-10.8%) of 79 parasite isolates, and individuals without malaria had an increase in IgG recognition to 8.1% (95% CI, 6.0%-10.2%) and a decrease in IgG recognition to 11.9% (95% CI, 7.0%-16.8%) of 79 parasite isolates. Most newly acquired IgG responses were against parasite isolates expressing VSAs(SM) that are frequently recognized by IgG.

CONCLUSIONS: Anti-VSA IgG levels decrease in the absence of infection, and an episode of clinical malaria induces IgG against a range of VSAs, particularly VSAs(SM).