Morphological and biochemical characterization of Procambarus clarki blood cells

Morphological and cytochemical analysis of Procambarus clarki hemocytes demonstrated three cell types: hyaline, semigranular, and granular. Hyaline cells showed a higher nuclear/cytoplasmic ratio with few small electron-dense granules in the cytoplasm. Semigranular cells presented numerous round or oval eosinophilic granules (0.40-0.78 micron). Granular cell contained large eosinophilic granules (1.79-3.05 microns). Ultrastructurally, all cells showed microtubules near the borders, a poorly developed Golgi complex, and secretory-type electron-dense particles. No mitotic figures were seen. Cell monolayers showed three morphologically distinct cell types (composed of flattened and well-spread cells) depending on the presence and size of granules (hyaline, semigranular, and granular). No sex-related differences could be documented in cell features or proportions. Cytochemical studies showed that the three cell types were positive for acid phosphatase. Granular and semigranular cells were also positive for nonspecific esterase. Phenoloxidase activity was localized only in granular and semigranular hemocytes, and peroxidase activity was observed only in the granular hemocytes. These results may suggest that the semigranular and granular hemocytes participate in the prophenoloxidase system and also in phagocytic or cytotoxic function.