IN-VITRO DIFFERENTIATION OF EOSINOPHILIC GRANULAR CELLS IN RENIBACTERIUM-SALMONINARUM INFECTED GILL CULTURES FROM RAINBOW-TROUT

Gill explants were maintained for one week in culture, and infected wi th R. salmoninarum. The explants were collected at two weeks post-infe ction and processed for ultrastructural examination. A marked tissue r eaction occurred in the infected explants in contrast with the control (non-infected) cultures, partially resembling an inflammatory respons e, and involving a marked increase in the number of eosinophilic granu lar cells. Several stages were identified from non-granulated precurso rs to mature eosinophilic granular cells, the earlier ones being close ly apposed to fibroblasts. The ultrastructural images suggest that mat ure eosinophilic granular cells showed a chronic, non-anaphylactic, de granulation. Although the major extracellular products of R. salmonina rum may elicit the differentiation and degranulation of the EGCs, the possibility of these phenomena being cytokine-driven is discussed. The se results demonstrate that eosinophilic granular cells are able to di fferentiate in situ, thus reinforcing the analogies between this cell type and mast cells. (C) 1996 Academic Press Limited