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 en hanced the protective effect of an i.p.-administered furunculosis vacc ine in salmon. In the present work, the peritoneal cell responses to y east glucan, glycogen, Freund's incomplete adjuvant (FIA) and saline w ere compared. Whereas saline gave no detectable peritoneal cell respon se, injection of the three other agents resulted in accumulation of ma crophages, neutrophils and thrombocytes in the peritoneal cavity 2-22 days later. Glucan and glycogen gave maximum leucocyte responses 2 day s after injection, whereas the number of leucocytes after FIA injectio n showed a continuous increase during the 22-day experimental period. Two days after injection, macrophages dominated in the leucocyte respo nse to yeast glucan, whereas neutrophils dominated in response to glyc ogen and FIA. At 8 and 22 days post-injection of yeast glucan and FIA, thrombocytes represented the largest fraction of peritoneal cells. Ex cept for an elevated number of neutrophils 3 weeks after injection, i. p. administration of yeast glucan gave no significant change in leucoc yte numbers from the head kidney. On the other hand, head kidney macro phages from glucan-treated fish showed an increased ability to kill a virulent strain of Aeromonas salmonicida.