Purity >95% as determined by SDS-PAGE. Tumor necrosis factor alpha (TNF?) is an inflammatory cytokine secreted by macrophages, monocytes, neutrophils, T cells, and NK-cells following stimulation by bacterial lipopolysaccharide (LPS). TNF? signal activation occurs through two receptors, TNFR1 and TNFR2. TNFR1 is expressed on most cell types, unlike TNFR2, which is expressed mainly on immune cells. TNF? functions to stimulate phagocytosis in macrophages, chemoattract neutrophils, increase insulin resistance, and induce fever.