The presented information reflects a state-of-the-art summary of the pleiotropic effects of IL-10 in vitro and in vivo and will contribute to our understanding of the role of ILj-10 in the immune system and its potential clinicial utility in the near future. The book contains chapters in which the in vitro biological effects of IL-10 on both mouse and human lymphoid and myeloid cells are reviewed. In addition, the role of IL-10 in transplantation, parasite infections, inflammation, infectious diseases and bone formation is described. The effects of IL-10 in vivo are presented, describing an IL-10 transgenic mouse model, the IL-10 "knock-out" mouse, and the capacity of IL-10 to prevent lethal toxic shock in mice.