Bioactivity studies of rainbow trout (Oncorhynchus mykiss) interleukin-6: Effects on macrophage growth and antimicrobial peptide gene expression

► The function of a fish IL-6 is studied for the first time in rainbow trout. ► Trout IL-6 expression is induced by LPS, polyI:C, IL-1β and IL-6 itself. ► rtIL-6 rapidly induces STAT3 phosphorylation and promotes macrophage growth. ► rtIL-6 instantly and transiently up-regulates the expression of signalling molecules. ► rtIL-6 induces a long lasting expression of the antimicrobial peptide genes.