Morphological and functional characterization of the oyster Crassostrea gasar circulating hemocytes: Cell types and phagocytosis activity

International audienceHemocytes are the circulating cells of the hemolymph of oysters and are responsible for numerous physiologicalfunctions, including immune defense. The oyster Crassostrea gasar is a native species inhabiting mangrove habitatand is of great commercial interest, cultured throughout the Brazilian coast, mainly in the north and northeast.Despite its commercial importance, little is known about its immunological aspects and defense cells, the hemocytes.This work aimed to morphologically characterize hemocytes of the oyster C. gasar and to study one ofthe main cellular defense response, phagocytosis, using light microscopy and flow cytometry. The results showedthe presence of six hemocyte populations in C. gasar hemolymph. These comprise of large and small granulocytes,large and small hyalinocytes, blast-like cells and a rare type classified as vesicular or serous hemocytes.Hyalinocytes were highly abundant and the most heterogeneous cell population, while small granulocytes, alongwith vesicular hemocytes were the less abundant population. Hemocytes of C. gasar oysters demonstrated capabilitiesto phagocytose three different types of particles tested: zymosan A, latex particles and Escherichia coli,indicating a broad defense capacity. The zymosan A were the most engulfed particles, followed by beads, mainlyphagocytized by granulocytes, the most phagocytic cells, and finally E. coli, which were the least phagocytized.This study is the first characterization of C. gasar oyster hemocytes and will support future studies that aim tounderstand the participation of different hemocyte types in defense responses against pathogens and/or environmentalchanges