Figure 3: Protective immunity requires a Th1 response, and tumour necrosis factor (TNF) is needed as an additional, macrophage activating factor. With a mixed Th1-Th2 cytokine response, TNF becomes toxic and mediates the gross tissue destruction characteristic of active, progressive tuberculosis. Stress and corticosteroids tend to drive newly recruited T cells towards Th2 responses. The protective Th1 immunity, a characteristic feature of granuloma is regulated by two mechanisms firstly (1) IFN-gamma which is essential for granuloma formation, may limit the uncontrolled expansion of mycobacteriareactive T cells. Secondly, endogenous IL-10, produced during mycobacterial infections, can reduce IL-12 production from mycobacteria infected DC’s, migration of DC’s to draining lymph nodes and the expansion of IFN-gamma secreting T-cells. However, the effective dose of IFN-γ and timing is yet to be determined.