Immune defense mechanisms of Culex quinquefasciatus (Diptera : culicidae) against Candida albicans infection

Mosquitoes have an efficient defense system against infection. The cellular immune defense mechanism initiated by the mosquito Culex quinquefasciatus infected with the fungus Candida albicans was investigated in this study. D ifferences in the hemocyte counts in hemolymph perfused from uninoculated, saline-inoculated, and C. albicans-infected mosquitoes were compared using a light microscope. Phagocytosis was also investigated using electron micro scopy. Four types of hemocytes were identified in control mosquitoes: prohe mocytes (9.8%), plasmatocytes (38.8%), granular cells (44.2%), and oenocyto ids (7.3%). Between 3 and 18 h postinoculation the total hemocyte count was significantly higher in infected, compared to uninfected, mosquitoes. Diff erential hemocyte counts from infected mosquitoes at 3, 6, and 18 h after i noculation showed that the relative proportion of plasmatocytes (48.6, 50.7 , 45%) was higher and, concomitantly, the proportion of granular cells was lower (38, 36.8, 35%, respectively). Yeast cells were phagocytosed and limi ted growth was observed within the plasmatocytes. Melanized nodules were fo und attached to different insect tissues at 24 to 72 h following infection. These results suggest that phagocytosis, followed by nodule formation, was capable of clearing the hemolymph of yeast cells. (C) 2000 Academic Press.