Role of heat-labile serum factor or host complement in the inhibition ofPlasmodium falciparumsporogonic stages inAnopheles stephensiby gametocyte carriers' serological factors

Abstract

SUMMARYThis study investigated the significance of serum complement on transmission-reducing activity (TRA) of field sera from 24 infectedPlasmodium falciparumgametocyte carriers (from Cameroon) against cultured NF54P. falciparum.Laboratory-rearedAnopheles stephensiwere given infectious blood meals prepared either with sera from naïve Dutch donor (AB type) or pair-matched field serum samples, both with and without active complement. TRA of serum factors and host complement on mosquito infection rate and oocyst intensity were divided into the various components involved in the early stages of sporogony. The majority (>80%) of sera tested showed positive antibody titres to Pfs230, the relevant complement-dependent target of transmission-reducing mechanisms. Regardless of the presence of active complement, bloodmeals with field sera exhibited significantly lower infection rates and oocyst intensity than the control group. Serological reactivity in Capture-ELISA against Pfs230 was significantly correlated with the reduction of parasite infectivity. Contrary to our expectation, the presence of active complement in the mosquito bloodmeal did not increase parasite losses and therefore the magnitude of transmission reduction by individual immune sera. Our findings onP. falciparumare consistent with previous studies on animal hosts ofPlasmodium, indicating that earlyP. falciparumsporogonic stages may be insensitive to the antibody-dependent pathways of complement in human serum.