Immunomodulation of potassium diformate in juvenile grass carp (Ctenopharyngodon idella) after Aeromonas hydrophila infection: T-cell differentiation and cytokine production

Potassium diformate (KDF) is a green and safe feed additive to replace antibiotics in animal. Although a few studies have found that KDF improved disease resistance, the specific mechanisms have not been explored in depth. Therefore, the study aims to examine the effects of KDF on immune defense substances, inflammatory process, T cell differentiation, and related molecular expression in fish. The juvenile grass carp were selected from six groups after feeding graded levels of KDF (0.0, 1.5, 3.0, 4.5, 6.0 and 7.5 g/kg) for 70 days. Then 6-day challenge experiment was performed by intraperitoneal injection Aeromonas hydrophila. Appropriate levels of KDF increased the lysozyme and acid phosphatase activities, the complement 3 and complement 4 contents in the head kidney and spleen of juvenile grass carp. Meanwhile, Appropriate addition levels of KDF down-regulated the abundances of TNF-alpha, IL-2, IL-6, IL-8, IL-1 beta, IL-12, IL-22, IL-17D, T-bet and ROR gamma t (ROR gamma 2) mRNA and upregulated the abundances of TGF-beta, IL-4, IL-10, GATA3, FOXP3, CD4, MHCII alpha and MHCII beta mRNA in the head kidney and spleen. Besides, appropriate levels of KDF down-regulated the mRNA levels of IKK gamma (not IKK alpha), IKK beta, NF-kappa B p65 (not p52), STAT1, STAT4, and the protein level of NF-kappa B p65, up-regulated the mRNA levels of I kappa B alpha, JAK1, JAK2, JAK3, STAT3b1, STAT3b2 (not STAT3a), STAT5b, STAT6, and the protein level of p-STAT3Tyr705. The appropriate levels of KDF enhanced the immune defense and mediated the inflammatory process that might be related to T cell differentiation probably via JAK-STATs and NF-kappa B signalings in fish.