Morphologic, cytometric and functional characterization of the common octopus (Octopus vulgaris) hemocytes

•Octopus vulgaris hemocytes were characterized by optical, electron microscopy and flow cytometry.•Two types of cells: large and small granulocytes were found in the octopus hemolymph.•Large granulocytes showed higher phagocytosis and respiratory burst than small ones.•The highest nitric oxide production was induced by zymosan, PMA and LPS respectively.•The three stimuli induced the highest nitric oxide production at 3 h of incubation.

The hemocytes of Octopus vulgaris were morphologically and functionally characterized. Light and electron microscopy (TEM and SEM), and flow cytometry analyses revealed the existence of two hemocyte populations. Large granulocytes showed U-shaped nucleus, a mean of 11.6 μm ± 1.2 in diameter with basophilic granules, polysaccharide and lysosomic deposits in the cytoplasm. Small granulocytes measured a mean of 8.1 μm ± 0.7 in diameter, and have a round nucleus occupying almost the entire cell and few or not granules in the cytoplasm. Flow cytometry analysis showed that large granulocytes are the principal cells that develop phagocytosis of latex beads (rising up to 56%) and ROS after zymosan stimulation. Zymosan induced the highest production of both ROS and NO. This study is the first tread towards understanding the O. vulgaris immune system by applying new tools to provide a most comprehensive morpho-functional study of their hemocytes.