Ultrastructural and functional characterization of circulating hemocytes from the freshwater crayfish Astacus leptodactylus: cell types and their role after in vivo artificial non-self challenge

The freshwater crayfish Astacus leptodactylus (Eschscholtz, 1823) is an important aquacultured decapod species as well as an invasive speciesin some European countries. In the current investigation we characterized the different classes of circulating blood cells in A. leptodactylus bymeans of light and electron microscopy analysis and we explored their reaction to different latex beads particles in vivo by total and differential cellcounts at 0.5, 1, 2 and 4 h after injections. We identified hemocytes by granule size morphometry as hyaline hemocytes with no or rare tinygranules, small granule hemocytes, unimodal medium diameter granule hemocytes and both small and large granule containing hemocytes. Thelatter granular hemocytes showed the strongest phenoloxidase L-DOPA reactivity both in granules and cytoplasm. A. leptodactylus respond toforeign particles with strong cellular immune responses. All treatments elicited a total hemocyte increase with a conspicuous recruitment of largegranule containing hemocytes. All hemocyte types mounted some phagocytic response but the small granule hemocytes were the only onesinvolved in phagocytic response to all foreign particles with the highest percentages. These results (1) depict the variability in decapod hemocytefunctional morphology; (2) identify the small granule hemocyte as the major phagocytic cell; (3) suggest that the rather rapid recruitment of largegranule hemocyte in all treatments plays a relevant role by this hemocyte type in defense against foreign particles, probably in nodule formation.# 2006 Elsevier Ltd. All rights reserved.