Yeast cell walls stimulate viability, respiratory burst, and phagocytosis in channel catfish (Ictalurus punctatus) head-kidney macrophages

Yeast cell wall (YCW) preparations are important nutritional additives in the aquaculture industry. Head-kidney macrophages play important roles in innate immune functions in fish. However, the mechanisms underlying their stimulation are not yet characterized. The purpose of this study was to investigate the effects of YCW on immunological functions of channel catfish (Ictalurus punctatus) head-kidney macrophages. Our results showed that YCW preparations not only improved the proliferation and phagocytosis of macrophages but also induced the secretion of reactive oxygen species (ROS), nitric oxide (NO), inducible nitric oxide synthase (iNOS), and cytokines, such as tumor necrosis factor-α (TNF-α) and interleukin 1β (IL-1β). At a concentration of 500.0 μg/mL, YCW preparations stimulated macrophage proliferation and phagocytosis to 1.98 and 1.8 times, respectively, when compared with the negative group. Equally, YCW preparations raised the production of NO by inducing iNOS and ROS in a concentration-dependent manner. Furthermore, these preparations enhanced TNF-α and IL-1β mRNA levels to multiple digits from 1.2 to 3.0 times, respectively. In conclusion, the stimulatory effects of YCW on the phagocytic activity of the fish macrophages were associated with respiratory bursts coupled with nitric oxide production.