In vivo cortisol administration suppresses the in vitro primary immune response of winter flounder lymphocytes

Abstract

Prolonged (24-day) administration of cortisol to adult winter flounder, Pleuronectes americanus , was found to decrease the in vitro primary immune response of splenic lymphocytes as measured by the passive haemolytic plaque assay. Intraperitoneal implantation of fish with cortisol mixed into a vegetable shortening and cocoa butter vehicle resulted in elevated serum cortisol levels that were within physiological ranges. Existing techniques for piscine lymphocyte culture were modified for use with winter flounder. Longer durations of elevated serum cortisol in the fish produced a more marked suppression of the plaque-forming cell (PFC) response. The suppression was evident as early as 10 days postimplantation when winter flounder cultures were stimulated for 14 days with trinitrophenyl-keyhole limpet haemocyanin (TNP-KLH). Suppression of the PFC response was not apparent until 17 days postimplantation in those cultures stimulated with trinitrophenyl-lipopolysaccharide (TNP-LPS) and was less apparent when the culture period was lengthened from 9 days to 14 days. Our results indicate that the in vitro primary PFC response can be used to evaluate the presence of chronic stress in fish.