PERITONEAL AND HEAD KIDNEY-CELL RESPONSE TO INTRAPERITONEALLY INJECTED YEAST GLUCAN IN ATLANTIC SALMON, SALMO-SALAR L

Previous studies have shown that intraperitoneal (i.p.) injection of a yeast cell wall glucan into Atlantic slamon, Salmo salar L., resulted in increased resistance to bacterial pathogens and that the glucan enhanced the protective effect of an i.p.-administered furunculosis vaccine in salmon. In the present work, the peritoneal cell responses to yeast glucan, glycogen, Freund's incomplete adjuvant (FIA) and saline were compared. Whereas saline gave no detectable peritoneal cell response, injection of the three other agents resulted in accumulation of macrophages, neutrophils and thrombocytes in the peritoneal cavity 2-22 days later. Glucan and glycogen gave maximum leucocyte responses 2 days after injection, whereas the number of leucocytes after FIA injection showed a continuous increase during the 22-day experimental period. Two days after injection, macrophages dominated in the leucocyte response to yeast glucan, whereas neutrophils dominated in response to glycogen and FIA. At 8 and 22 days post-injection of yeast glucan and FIA, thrombocytes represented the largest fraction of peritoneal cells. Except for an elevated number of neutrophils 3 weeks after injection, i.p. administration of yeast glucan gave no significant change in leucocyte numbers from the head kidney. On the other hand, head kidney macrophages from glucan-treated fish showed an increased ability to kill a virulent strain of Aeromonas salmonicida.