Insects use a circulatory system to transport molecules and cells, and an immune system to combat infections. In the African malarial mosquito Anopheles gambiae, the immune and circulatory systems are functionally integrated, as hemocytes (immune cells) reside near the ostia (valves) of the heart. These heart-associated hemocytes are advantageous when fighting an infection because they are in the regions that experience the swiftest hemolymph flow, and hence, are in the locations where they are most likely to encounter and phagocytose invading pathogens. However, whether this functional integration between the immune and circulatory systems is conserved across insect evolution remains unknown. Therefore, we analyzed insects from 16 orders representing 51 families and tested whether an infection results in a concentrated immune response on the heart. We found that infection induces hemocyte and pathogen aggregation on the heart of insects in 14 orders. These data suggest that the interaction between the immune and circulatory system is conserved in class Insecta.
