**5.4 Mycobacterium infection**

The TNFα -/- mice or the IL-6 -/- mice demonstrated that TNF is critical for initiation of the granulomatous response, and IL-6 plays a key role in the granuloma maintenance response (Welsh et al., 2008). Unlike Il-6 -/- mice, TCZ does not completely inactivate the IL-6 system because TCZ works as a competitive inhibitor of IL-6. Moreover, TCZ, unlike TNF inhibitors, does not inhibit *M. tuberculosis* antigen-induced interferon gamma (IFN-γ) production (Ogata et al., 2010b). TNF inhibitors increase the risk of infection or reactivation of *M. tuberculosis* while TCZ does not in clinical practice. Of course, TCZ should not be used in the patients with active mycobacterium infection. However, TCZ may be a candidate for intractable RA patients with mycobacterium infection which is treated. A patient with intractable RA was treated with TCZ without aggravation of *M. avium* infection which had been treated in advance (Nakahara et al., 2010).
