These studies suggested that physical association of lysozyme c-1 with developing malaria parasites might protect them from mosquito defense responses. To investigate whether lysozyme c-1 binds to Plasmodium parasites in susceptible mosquitoes, we performed immunohistochemical analyses of midgut tissues from mosquitoes infected with P. berghei or P. falciparum. We verified the specificity of anti-lysozyme c-1 antibodies aLys-c-1 9122 and aLys-c-1 9124 against lysozyme c-1 obtained from mosquito salivary glands, conditioned media of An. gambiae cell line 4a3B and recombinant lysozyme c-1 produced in E. coli or baculovirus. Via Western blotting, we confirmed that these antibodies Quinalizarin specifically crossreacted with a protein approximating the expected molecular weight of 15 kDa in these samples. A preimmune serum from the same rabbit in which lysozyme c-1 antibodies were raised did not cross-react to lysozyme c-1 from any of the aforementioned sources. Further support for specific binding of these antibodies to lysozyme c-1 was derived from these observations. First, the peptide used for generation of 9122 and 9124 antibodies differed significantly from the sequences of other An. gambiae lysozymes at these residues but was nearly identical to the orthologous sequence from An. stephensi. Second, antibody 9122 did not cross-react with partially PF06650833 purified recombinant lysozymes c-2 and c-4 produced in E. coli or with proteins from mouse blood. We surveyed over 300 parasites from nine separate infections of P. berghei in An. gambiae, more than 700 parasites from two infections of P. falciparum in An. gambiae, and 30 parasites from one infection of P. falciparum in An. stephensi for lysozyme c-1 labeling using anti-lysozyme c-1 antibodies. In vivo, some ookinetes showed a variable degree of labeling but 80�C90% ookinetes were not labeled at 22�C24 h. Similarly, in vitro cultured ookinetes pre-incubated with recombinant lysozyme c-1 did not subsequently cross-react with these antibodies. In contrast, the 9122 and 9124 antibodies bound to nearly all oocysts of P. berghei and P. falciparum in vivo at 2 days and 5 days post-infection.