The Plasmodium circumsporozoite protein is involved in mosquito salivary gland invasion by sporozoites.

Plasmodium sporozoites develop in oocysts on the midgut wall of the mosquito and are released into the hemocoel. Approximately 15-20% of oocyst sporozoites will successfully attach to and invade salivary glands, their target organ. We have previously shown that the major surface protein of sporozoites, the circumsporozoite (CS) protein, binds specifically to salivary glands and not to other mosquito organs exposed to circulating hemolymph. In addition, a peptide from the N-terminal portion of CS protein inhibits binding of the protein to the glands. In this study, we have extended these findings and show that both the protein and the peptide can inhibit sporozoite invasion of salivary glands.