Rapid regulation of hemocyte homeostasis in crayfish and its manipulation by viral infection

In crustaceans, the number of circulating hemocytes changes rapidly in response to pathogen infection and injury, but the underlying mechanism remains unclear. In this study, we investigated the regulation of hemocytes homeostasis in crayfish after hemolymph withdrawal. We showed that the circulating hemocytes increased by over 2 folds within 1 h post hemolymph withdrawal and returned to normal level within 8 h. New hemocytes produced by hematopoiesis accounted for <6.5% of the total replenishment, implying a major role of sessile hemocytes in rapid hemocyte supply. Moreover, when hemocytes were transplanted, the extra cells were efficiently stored, mainly in the gill. These stored cells could be released into circulation immediately on demand. Notably, the rapid regulation of hemocyte homeostasis was abolished by white spot syndrome virus infection. These data indicate that the adjustment between the sessile and circulating pools of hemocytes may be the major route for the rapid regulation of circulating hemocytes in crayfish, and this process may be altered by pathogen infection.