ABSTRACT

IL-10 is a dichotomous functional cytokine. It has characteristics of being both an immuno­suppressive and immunostimulatory cytokine. In the setting of many infectious diseases including some viral infections, IL-10 administration prevents infected mice from pro­ gressing. IL-10 activates the cytolytic function of NK cells as well as that mediated by acti­ vated/memory CD 8+T cells. In a second stage following infection, IL-10 released from host cells often protects the host from secondary hyperinflammation, capable of damaging tissues, whereas endogenous IL-10 often imposes a suppressive function on CD 4+ T cells and antigen presenting cells. The IL-10 effects, modulating hyperinflammation can also induce regulatory T cells. In contrast, IL-10 production generated by or stimulated direedy by some bacteria or protozoa infected D C may induce regulatory T cells, thereby helping microbes to aggressively invade host tissues. Indeed, IL-10'/_ mice are protected from some infectious diseases. In the setting of tumor immunobiology, IL-10 expression appears to promote rejection o f most ex­ perimental tumors. Thus, IL-10 release regulates innate immune mechanisms important for controlling microbes and playing a role in the chronic inflammatory response associated with tumorigenesis or secondary host defenses limiting progression of infection and host tissue damage.