In vivo kinetics of cytokine expression during peritonitis in carp: Evidence for innate and alternative macrophage polarization

Despite the discovery of many cytokine genes in fish, knowledge on their functional homology is limited. To enlighten the biological function of inflammation-related mediators, we studied their kinetics of gene expression during peritonitis in carp. Zymosan-induced intraperitoneal influx of phagocytes reached a maximum at 24 h. In peritoneal leukocytes (PTL) up-regulation of IL-1β, TNF-α, CXCa, and chemokine receptor CXCR1 preceded this peak. Delayed up-regulation of these genes in the head kidney (HK) indicates emigration of antigen-presenting cells from peritoneum into HK and/or systemic spreading of inflammation. In turn, early increase in expression of anti-inflammatory genes in HK (6 h) precede their up-regulation in the focus of inflammation. In PTL peaks of IL-10 and arginase 2 expression were recorded at 96 and 168 h, respectively. These results give evidence that carp macrophages in vivo differentiate into a continuum of different activation states with innate and alternative activation representing the extremes.