Effect of corticosteroids on viability and proliferation of the rainbow trout monocyte/macrophage cell line, RTS11

Cortisol at 1000 and 100 ng/ml, and less consistently at 10 ng/ml, inhibited increases in cell number and 3H-thymidine incorporation by cultures of the rainbow trout (Oncorhynchus mykiss) monocyte/macrophage cell line, RTS11. Cell viability was not altered by cortisol, although a small decline in the capacity of cultures to reduce the redox dye, Alamar Blue was observed. In cortisol-treated cultures, more round and fewer spread cells were evident. Similar results were observed with dexamethasone but not cortisone. The glucocorticoid receptor antagonist, RU-486, prevented the effects of cortisol on RTS11 proliferation, and shape. In co-culture with the spleen stroma cell line (RTS34st) or in medium conditioned by RTS34st, the proliferation of RTS11 was enhanced. Treating RTS11/RTS34st co-cultures or RTS11 cultures in RTS34st conditioned medium with cortisol did not inhibit RTS11 proliferation. Overall these experiments suggest that proliferation of rainbow trout macrophages is regulated by cortisol, but the effect is modulated by the cellular micro-environment, possibly through the release of cytokines.