Anopheles gambiae hemocytes exhibit transient states of activation

Hemocytes are crucial players of the mosquito immune system and critically affect transmission of pathogens including malaria parasites. We and others discovered previously that a blood meal is a major immune stimulus for mosquito hemocytes. To determine whether these blood meal-induced hemocyte changes in Anopheles gambiae constitute steps in cell differentiation or demonstrate transient cell activation, we analyzed the temporal pattern of these changes over the first three days post blood meal (dpbm). Flow cytometry and immunofluorescence analyses revealed a global shift of the entire hemocyte population, peaking at 1 dpbm. All hemocyte activation markers returned to pre-blood meal baseline levels within the following 24-48 h. Our observations are consistant with An. gambiae hemocytes undergoing transient activation rather than terminal differentiation upon blood feeding. Interestingly, the temporal pattern followed the gonotrophic cycle of the mosquito, strongly suggesting hormonal control of mosquito hemocyte activation and deactivation.