Interleukin 1 receptor antagonist (IL-1RA) is a 17.26 kDa member of IL-1 family with 153 amino acid residues. IL-1RA is expressed by peripheral blood cells, lungs, spleen, liver and is secreted from monocytes, macrophages, neutrophils, and other cells. Inhibits the activity of interleukin-1 by binding to receptor IL1R1. IL-1RA can modulate a variety of interleukin-1 related immune and inflammatory responses, particularly in the acute phase of infection and inflammation.