Cytokine expression in leucocytes and gut cells of rainbow trout, Oncorhynchus mykiss Walbaum, induced by probiotics

Understanding how the various host cells respond to probiotic bacteria in vitro may provide important insight into elaborate immune responses triggered by beneficial bacteria. The aim of this study was to investigate the detailed pattern of the mRNA expression of cytokines (IL-1β, IL-8, TNF-α and TGF-β) in head kidney (HK) leucocytes and gut cells isolated from rainbow trout (Oncorhynchus mykiss Walbaum) after co-culturing with live probiotics. HK leucocytes and gut cells adjusted to 5 × 106 and 2 × 106 ml−1, respectively, in L-15 medium containing 25% decomplemented FCS and 300 mg l−1l-glutamine were co-cultured with Carnobacterium maltaromaticum B26 and C. divergens B33 at an multiplicity of infection of 25 for 6 and 12 h. Quantitative real-time reverse transcriptase polymerase chain reaction using SYBR Green I was employed to determine the mRNA expression of studied genes. Although neither probiotic strains significantly induced mRNA of the cytokines in gut cells, expression ratios of IL-1β and TNF-α of HK cells were significantly higher, suggesting that these bacteria can stimulate innate immunity in rainbow trout.