Effects of hemocytes of Anopheles stephensi on the melanization of oocysts of Plasmodium yoelii

Aim To explore the mechanism of melanotic encapsulation of Plasmodium yoelii by Anopheles stephensi Methods Mosquito midgets samples were observed by transmission electron microscope Hemocytes collected from adult female An stephensi of four groups,no blood feeding,normal blood feeding,nitroquine administrated and infection of P yoelii,were detected by RT PCR and in situ hybridization Results In the nitroquine administrated group,oocysts were found markedly degenerated and one or more hemocytes could be found around the oocytes The expression of An stephensi PPO gene in various groups and tissues,in which a specific 470bp fragment was amplified and detected only in the hemocytes,but not in the midguts and salivary glands from 4 groups mosquitoes Total RNA samples were analyzed from An stephensi hemocytes by in situ hybridization,using digoxigenin labelled PPO cDNA as probes The stronger positive signal was detected in the nitroquine administrated group Conclusion The expression of the prophenoloxidase gene was only in mosquito hemocytes An stephensi hemocytes,especially granulocytes,play a critical role in the melanization of P yoelii oocyst This may provide rewarding information with regard to Anopheles/Plasmodium interactions