Cytokines have an essential role in host resistance to TB infection, being first demonstrated in murine infection models [19] and later validated by severe mycobacterial disease findings in patients with mutations in the IFN-γ and IL-12 signaling pathways and rheumatoid arthritis or Crohn's disease patients treated with TNF-α blockade [19, 31]. The gene discussed is TNF; the disease is rheumatoid arthritis.