Increased resistance to mycobacterial infection in the absence of interleukin-10

Interleukin-10 (IL-10) down-regulates T helper type 1 cell and macrophage f unctions. As IL-10 is induced along with tumour necrosis factor (TNF) and I L-12 in mycobacterial infection, we asked whether endogenous IL-10 plays a role in the antimycobacterial response. We demonstrate here that IL-10-defi cient mice eliminate Mycobacterium bovis Calmette-Guerin bacillus faster th an wild-type mice. Granulomas are significantly larger, containing more CD- 11b- and CD11c-positive antigen-presenting cells and T cells, and the expre ssion of major histocompatibility complex class II and intracellular adhesi on molecule-1 is increased. Macrophages in granulomas of IL-10-deficient mi ce express high levels of TNF, acid phosphatase and inducible nitric oxide synthase (iNOS). Finally, an increased cutaneous delayed-type hypersensitiv ity reaction to mycobacterial proteins is further evidence of an augmented cell-mediated immune response. In conclusion, the cell-mediated immunity is enhanced in the absence of IL-10, resulting in a robust granuloma response , which accelerates the clearance of mycobacteria. Therefore, endogenous IL -10 attenuates mycobacterial immunity.