Interleukin-1 family member 5 is a protein that in humans is encoded by the IL1F5 gene.

The protein encoded by this gene is a member of the interleukin 1 cytokine family. This cytokine was shown to specifically inhibit the activation of NF-kappaB induced by interleukin 1 family, member 6 (IL1F6). This gene and eight other interleukin 1 family genes form a cytokine gene cluster on chromosome 2. Two alternatively spliced transcript variants encoding the same protein have been reported. [provided by RefSeq, Jul 2008].
Function: Is a highly and a specific antagonist of the IL-1 receptor-related protein 2-mediated response to interleukin 1 family member 9 (IL1F9). Could constitute part of an independent signaling system analogous to interleukin-1 alpha (IL-1A), beta (IL-1B) receptor agonist and interleukin-1 receptor type I (IL-1R1), that is present in epithelial barriers and takes part in local inflammatory response.