Maturation of fish erythrocytes coincides with changes in their morphology, enhanced ability to interact with Candida albicans and release of cytokine-like factors active upon autologous macrophages

Erythrocytes from the rainbow trout Salmo gairdneri Richardson (Salmo g.R.) were classified into immature and mature populations, respectively, by measuring longitudinal diameters. More elongated fish erythrocytes (FE), classified as mature cells, were those interacting with Candida albicans (CA) in a higher frequency in terms of either binding to the fungus or its intracellular engulfment. At the same time, in the rosetting phenomenon more elongated mature FE surrounded macrophages (Mcircle divide) phagocytosing CA. Finally, FE activated by CA released in the supernatants cytokine-like factors able to modulate Mcircle divide functions. In particular, these active supernatants were analyzed for their capacity to inhibit Mcircle divide migration Macrophage Inhibition Factor (MIF) activity and enhance Mcircle divide phagocytosis. Both activities were detected in supernatants from CA stimulated FE but not in control supernatants. MIF activity could play a role in the accumulation of Mcircle divide in the context of functional rosettes, while the factor enhancing Mcircle divide phagocytosis could promote clearance of CA in a more efficacious way.