Identification of a Novel IL-1 Cytokine Family Member in Teleost Fish

A novel IL-1 family member (nIL-IF) has been discovered in fish, adding a further member to this cytokine family. The unique gene organization of nIL-1F, together with its location in the genome and low homology to known family members, suggests that this molecule is not homologous to known IL-1F. Nevertheless, it contains a predicted C-terminal beta-trefoil structure, an IL-1F signature region within the final exon, a potential IL-1 converting enzyme cut site, and its expression level is clearly increased following infection, or stimulation of macrophages with LPS or IL-1 beta. A thrombin cut site is also present and may have functional relevance. The C-terminal recombinant protein antagonized the effects of rainbow trout rIL-1 beta on inflammatory gene expression in a trout macrophage cell line, suggesting it is an IL-1 beta antagonist. Modeling studies confirmed that nIL-IF has the potential to bind to the trout IL-1RI receptor protein, and may be a novel IL-1 receptor antagonist. The Journal of Immunology, 2009, 183: 962-974.