A recombinant cytokine chemically identical to or similar to interleukin-10 (IL-10) secreted by certain leukocytes with immunomodulatory activities. IL-10 is an anti-inflammatory cytokine, capable of inhibiting synthesis of pro-inflammatory cytokines, such as Interferon-gamma, IL-2, IL-3, TNF-alpha, and GM-CSF. However, it also has stimulatory effects on certain T cells, mast cells, and B cells, as well as inducing expression of class II major histocompatibility complex.