Abstract
Background: A transmission-blocking vaccine (TBV) can be a useful tool to reduce malaria infection in an endemic area. For a TBV, elicited antibody (either by itself or working with complement) has a critical role in the mechanism of action, which for most known TBV targets, blockade will occur within the mosquito. However, no study has quantitively assessed the longevity of ingested antibody in Anopheles mosquito vectors. Methods: A mixture of mouse or human monoclonal antibody (mAb), human red blood cells and human serum were fed to An. stephensi mosquitoes, and their midguts were collected at multiple time points (0 to 48 hours; 12 mosquitoes at each time point) after feeds. The reactivity of antibodies against target antigen (integrity of antigen-binding region of the antibody) in each midgut was assessed by ELISA. For one mouse mAb, integrity of antibody constant region was also determined by western blot (WB) with a mouse-specific secondary antibody.Results: First, the half-life of mouse anti-Pfs25 mAb, 4B7, was determined both by ELISA and WB in three independent assays. When the ELISA and WB signals were plotted against time after feed, both data reasonably fit one-phase exponential decay models (R2 B 0.70), and the half-lives were estimated as 8.6 hours by ELISA and 4.7 hours by WB. To determine whether the longevity was affected by target antigens or species of antibody, two human anti-Pfs25 mAbs (AB1245 and AB2544), one human anti-Pfs48/45 mAb (TB31F), and one mouse anti-Pfs230 mAb (15A4-1B12) were examined by ELISA in two or three independent assays. The ELISA results of each additional mAb also reasonably fit to a one-phase exponential decay model (R2 a 0.78), and the half-lives of those mAbs were similar to that of 4B7 (7.2 to 9.3 hours), except AB1245 which showed a half-life of 4.6 hours. Conclusions: Depending on the methods of detection and mAbs used, the longevity of ingested antibody varied around 2-fold, but all estimated half-lives were < 10 hours. These data suggest a TBV with antibody dependent mechanism of action(s) is more likely to succeed when targeting earlier stages of parasites (or parasite interaction) in mosquitoes.
Half-life of Ingested Antibodies in Anopheles Stephensi Mosquito Is Less Than 10 Hours
