Submitted June 25, 2007
Accepted November 22, 2007
Inhibition of collagen-induced platelet aggregation by anopheline anti-platelet protein, a saliva protein from a malaria vector mosquito
Shigeto Yoshida*, Toshiki Sudo, Masashi Niimi, Lian Tao, Bing Sun, Junichi Kambayashi, Hiroyuki Watanabe, Enjou Luo, and Hiroyuki Matsuoka
Division of Medical Zoology, Department of Infection and Immunity, Jichi Medical University, Shimotsuke, Japan
First Institute of New Drug Discovery, Otsuka Pharmaceutical Co. Ltd., Tokushima, Japan
Otsuka Maryland Medicinal Laboratories, Rockville, MD, United States
* Corresponding author; email: shigeto{at}jichi.ac.jp.
During blood feeding, mosquitoes inject saliva containing a mixture of molecules that inactivate or inhibit various components of the hemostatic response to the bite injury as well as the inflammatory reactions produced by the bite, in order to facilitate the ingestion of blood. However, the molecular functions of the individual saliva components remain largely unknown. Here, we describe anopheline anti-platelet protein (AAPP) isolated from the saliva of Anopheles stephensi, a human malaria vector mosquito. AAPP exhibited a strong and specific inhibitory activity toward collagen-induced platelet aggregation. The inhibitory mechanism involves direct binding of AAPP to collagen, which blocks platelet adhesion to collagen and inhibits the subsequent increase in intracellular Ca2+ concentration ([Ca2+]i). The binding of AAPP to collagen effectively blocked platelet adhesion via GPVI and integrin 
2
1. Cell adhesion assay showed that AAPP inhibited the binding of GPVI to collagen type I and III without direct effect on GPVI. Moreover, intravenously administered recombinant AAPP strongly inhibited collagen-induced platelet aggregation ex vivo in rats. In summary, AAPP is a malaria vector mosquito-derived specific antagonist of receptors that mediate the adhesion of platelets to collagen. Our study may provide important insights for elucidating the effects of mosquito blood feeding against host hemostasis.
