Morphological and cytochemical characterization of female Anopheles albimanus (Diptera: Culicidae) hemocytes

Hemocytes of 2- to 3-d-old female Anopheles albimanus Wiedemann are described by morphology, cytochemistry, and functional criteria. Supplemented Grace's insect medium in a modified Foley's perfusion method was used to obtain hemolymph from An. albimanus. Morphological analysis indicated 3 types of hemocytes were present, prohemocytes, plasmatocytes, and granular cells. Prohemocytes were small round cells with a high nuclear/cytoplasmic ratio. Plasmatocytes were the most abundant cell types in the hemolymph, and appeared as small to large and spindle-shaped cells with round or elongate nucleus, variable number of vacuoles, small granules, and pseudopodia. Granular cells were small to large and round with a large number of cytoplasmic granules, vacuoles, and numerous filopodia. Ultrastructurally, prohemocytes were undifferentiated with abundant free ribosomes and with few small electron-dense granules. Plasmatocytes were rich in mitochondria, rough endoplasmic reticulum, free ribosomes, small electron-dense granules, numerous peripheral vacuoles and with an important organelle polarization. Granular cells contained numerous large electron-dense granular inclusions and vacuoles. Cytochemical studies showed that plasmatocytes and granular cells have cationic bactericidal proteins. Only granular cells showed phenoloxidase and probably lysosomal activities. In vitro functional studies demonstrated that both plasmatocytes and granular cells were able to attach to glass slides, and only plasmatocyte had phagocytic activity and motility. These results characterize the hemocytes of An. albimanus and suggest that plasmatocytes and granular cells may have a role in defense responses to foreign organisms.