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Hemocyte-mediated phagocytosis and melanization in the mosquito Armigeres subalbatus following immune challenge by bacteria.

Hillyer JF, Schmidt SL, Christensen BM
Cell Tissue Res. 2003 313 (1): 117-27

PMID: 12838409 · DOI:10.1007/s00441-003-0744-y

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.

MeSH Terms (28)

Acid Phosphatase Animals Bacteria Bacterial Capsules Cell Adhesion Culicidae Escherichia coli Glycogen Granulocytes Green Fluorescent Proteins Hemocytes Histocytochemistry Immunity, Innate Immunohistochemistry Lectins Luminescent Proteins Mannose-Binding Lectins Melanins Micrococcus luteus Microscopy, Electron Microscopy, Fluorescence Microscopy, Immunoelectron Microscopy, Phase-Contrast Microspheres Monophenol Monooxygenase Phagocytosis Plant Lectins Wheat Germ Agglutinins

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