Disruption of Plasmodium falciparum development by antibodies against a conserved mosquito midgut antigen

Malaria parasites must undergo development within mosquitoes to be transmitted to a new host. Antivector transmission-blocking vaccines inhibit parasite development by preventing ookinete interaction with mosquito midgut ligands. Therefore, the discovery of novel midgut antigen targets is paramount. Jacalin (a lectin) inhibits ookinete attachment by masking glycan ligands on midgut epithelial surface glycoproteins. However, the identities of these midgut glycoproteins have remained unknown. Here we report on the molecular characterization of an Anopheles gambiae aminopeptidase N (AgAPN1) as the predominant jacalin target on the mosquito midgut luminal surface and provide evidence for its role in ookinete invasion. alpha-AgAPN1 IgG strongly inhibited both Plasmodium berghei and Plasmodium falciparum development in different mosquito species, implying that AgAPN1 has a conserved role in ookinete invasion of the midgut. Molecules targeting single midgut antigens seldom achieve complete abrogation of parasite development. However, the combined blocking activity of alpha-AgAPN1 IgG and an unrelated inhibitory peptide, SM1, against P. berghei was incomplete. We also found that SM1 can block only P. berghei, whereas alpha-AgAPN1 IgG can block both parasite species significantly. Therefore, we hypothesize that ookinetes can evade inhibition by two potent transmission-blocking molecules, presumably through the use of other ligands, and that this process further partitions murine from human parasite midgut invasion models. These results advance our understanding of malaria parasite-mosquito host interactions and guide in the design of transmission-blocking vaccines.