Morphological and functional characterization of hemocytes in cultivated mussel (Mytilus galloprovincialis) and effect of hypoxia on hemocyte parameters

Abstract

The circulating hemocytes of cultivated marine mussel (Mytilus galloprovincialis) were investigated using light microscopy and flow cytometry. In mussels two cell types, granulocytes and agranulocytes, were identified based on the existence of two subpopulations of cells differing by size and granularity level on light-scattered plots. Light microscopic observation confirmed the presence of cells with cytoplasmic granules and cells without granulation in hemolymph of mussels. The main type of cells in hemolymph were agranular cells amounting 78.4 ± 8.9% in mussels. Flow cytometry showed that the agranular hemocytes of the mollusks produce significantly less reactive oxygen species compared to granulocytes. Mussel were exposed for 24 h of hypoxia and immune functions including hemocyte mortality, proliferation and reactive oxygen species (ROS) production were analysed using flow cytometric methods. Granulocyte number was higher at low oxygen concentration than that at normoxia; agranulocytes number decreased, in contrast. The ROS production after hypoxic treatment was decreased compared to normoxia level. No significant changes in hemocyte mortality and proliferation were observed.