Periostial hemocyte aggregation on the surface of the mosquito heart

Mosquitoes respond to infection by mounting potent immune responses.  Many of these responses are mediated by hemocytes, which are immune cells that either circulate with the hemolymph or are attached to other tissues.  We have previously shown that when some pathogens enter the hemocoel of Anopheles gambiae, they induce the migration of hemocytes to specific regions of the heart (the portion of the dorsal vessel that is positioned in the abdomen), and that these regions correspond to the locations of the heart valves, or ostia.  Once near the ostia, these cells are called periostial hemocytes.  In this presentation, we will show that (1) immune responses on the surface of the heart occur following diverse immune stimuli, (2) the intensity of the heart-associated phagocytosis response corresponds with the density of periostial hemocytes, and (3) periostial hemocyte aggregation correlates with the pattern of hemolymph entry into the heart.  Altogether, these data detail a potent immune response that occurs on the surface of the primary circulatory organ of an insect.