Adaptability of carp neutrophilic granulocytes to environmental temperatures: spontaneous cytotoxic activity and cell-adherent activity

This study observed the adaptability of carp neutrophilic granulocytes possessing spontaneous cytotoxic activity to different environmental temperatures. To study the adaptability of neutrophilic granulocytes, two different temperatures (25° C and 10° C) were selected, both for rearing and forin vitroassays, in which the cytotoxicity and the adherent rate against K562 target cells were measured. The cytotoxicity and adherent rate of neutrophilic granulocytes from carp kept at 25° C for 30 days were higher when assayed at 25° C than when assayed at 10° C. On the other hand, in carp acclimated from 25° C to 10° C, the cytotoxicities and adherent rates, when assayed at 25° C, decreased with increasing acclimation times, eventually becoming smaller than the values obtained when assayed at 10° C. After the fish kept at 10° C for a long period were re-acclimated to 25° C, these activities assayed at 25° C again became higher than the activities assayed at 10° C. These results indicated that carp neutrophilic granulocytes adapt their cytotoxic activity and adherent activity to different environmental temperatures. A change in cellular composition in the head kidney was also observed in carp kept at different environmental temperatures. The percentage of neutrophilic granulocytes became higher and lymphocytes became lower in carp that were kept at 10° C for a long period compared with carp that were kept at 25° C for a long period.