Regulatory Role of T Cells Producing both Interferon γ and Interleukin 10 in Persistent Infection

IL-10 was originally described as a cytokine produced by Th2 cells and mediating antiinflammatory effects, by acting primarily on phagocytic cells and on antigen-presenting cells (1). IL-10 inhibits, in these cells, transcription and production of proinflammatory cytokines, such as TNF and IL-12, expression of MHC class II, and costimulatory molecules, as well as the production of reactive oxygen and nitrogen intermediates (1). In part through inhibition of IL-12 production and of costimulatory molecule expression on antigen-presenting cells, IL-10 has an overall suppressive effect on the generation of Th1 responses. In addition, IL-10 profoundly affects the bactericidal activity of phagocytic cells, allowing intracellular survival of pathogens such as Mycobacterium tuberculosis (2) and Leishmania major (3). In addition to inhibit the intracellular bactericidal mechanisms, IL-10 was shown to prevent TNF-mediated apoptosis of M. tuberculosis infected macrophages thus possibly facilitating...