Purity >95% by SDS-PAGE, MW: 21.9 kDa. Interleukin 6 (IL-6) is a cytokine that is expressed by T cells, macrophages, and muscle cells. IL-6 acts to stimulate an immune response upon infection or trauma. IL-6 has both pro-inflammatory and anti-inflammatory functions, is capable of promoting fever, and signals through the cell-surface type I cytokine receptor complex containing the IL-6Ra and gp130 chains. Human IL-6 is active on mouse and rat cells.