title: Hemocyte-mediated phagocytosis and melanization in the mosquito Armigeres subalbatus following immune challenge by bacteria.
abstract: Mosquitoes are important vectors of disease. These insects respond to invading organisms with strong cellular and humoral immune responses that share many similarities with vertebrate immune systems. The strength and specificity of these responses are directly correlated to a mosquito's ability to transmit disease. In the current study, we characterized the hemocytes (blood cells) of Armigeres subalbatus by morphology (ultrastructure), lectin binding, enzyme activity, immunocytochemistry, and function. We found four hemocyte types: granulocytes, oenocytoids, adipohemocytes, and thrombocytoids. Granulocytes contained acid phosphatase activity and bound the exogenous lectins Helix pomatia agglutinin, Galanthus nivalis lectin, and wheat germ agglutinin. Following bacteria inoculation, granulocytes mounted a strong phagocytic response as early as 5 min postexposure. Bacteria also elicited a hemocyte-mediated melanization response. Phenoloxidase, the rate-limiting enzyme in the melanization pathway, was present exclusively in oenocytoids and in many of the melanotic capsules enveloping bacteria. The immune responses mounted against different bacteria were not identical; gram(-) Escherichia coli were predominantly phagocytosed and gram(+) Micrococcus luteus were melanized. These studies implicate hemocytes as the primary line of defense against bacteria.
authors.affiliation: Department of Animal Health and Biomedical Sciences, University of Wisconsin-Madison, 1656 Linden Drive, Madison, WI 53706, USA.
authors.forename: Julián F
authors.initials: JF
authors.lastname: Hillyer
authors.forename: Shelley L
authors.initials: SL
authors.lastname: Schmidt
authors.forename: Bruce M
authors.initials: BM
authors.lastname: Christensen
mesh_terms: D000135:Acid Phosphatase / Q000032:analysis; D000818:Animals; D001419:Bacteria / Q000254:growth & development / Q000276:immunology*; D016667:Bacterial Capsules / Q000378:metabolism; D002448:Cell Adhesion / Q000502:physiology; D009033:Culicidae / Q000276:immunology / Q000382:microbiology / Q000502:physiology*; D004926:Escherichia coli / Q000235:genetics / Q000276:immunology; D006003:Glycogen / Q000032:analysis; D006098:Granulocytes / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D049452:Green Fluorescent Proteins; D006434:Hemocytes / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D006651:Histocytochemistry; D007113:Immunity, Innate / Q000276:immunology; D007150:Immunohistochemistry; D037102:Lectins / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics; D037241:Mannose-Binding Lectins / Q000378:metabolism; D008543:Melanins / Q000378:metabolism*; D016982:Micrococcus luteus / Q000276:immunology; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D008858:Microscopy, Phase-Contrast; D008863:Microspheres; D014442:Monophenol Monooxygenase / Q000032:analysis / Q000276:immunology / Q000502:physiology; D010587:Phagocytosis / Q000502:physiology*; D037121:Plant Lectins / Q000378:metabolism; D014909:Wheat Germ Agglutinins / Q000378:metabolism
chemical_list: C038095:Helix lectin; D037102:Lectins; D008164:Luminescent Proteins; D037241:Mannose-Binding Lectins; D008543:Melanins; D037121:Plant Lectins; D014909:Wheat Germ Agglutinins; C063117:snowdrop lectin; D049452:Green Fluorescent Proteins; D006003:Glycogen; D014442:Monophenol Monooxygenase; D000135:Acid Phosphatase