Interleukin-10 (IL-10), originally known as Cytokine Synthesis Inhibitory Factor (CSIF), is an 18.5 kD protein that shares over 80% sequence homology with the Epstein-Barr Virus protein BCRFI. The reported biological activities of IL-10, which may be interrelated, include inhibition of macrophage-mediated cytokine synthesis, suppression of the delayed type hypersensitivity response, and stimulation of the TH2 cell response, which results in elevated antibody production. The net effect of IL-10 action appears to be the inhibition of proinflammatory T cell mediated immunity. Recombinant human IL-10 (Cat No. 554611) is supplied as a frozen liquid comprised of 0.22 µm sterile-filtered aqueous buffered solution, containing glycerol and bovine serum albumin, with no preservatives. Recombinant human IL-10 is ≥ 95% pure as determined by SDS-PAGE analysis, and an absorbance assay based on the Beers-Lambert law. The endotoxin level is ≤ 0.1 ng per µg of human IL-10, as measured in a chromogenic LAL assay.