Several cytokines produced by T cells (IFNγ or TNF35, 36), myeloid cells (IL-1, IL-12, TNF, IL-6 32, 37, 38, 39, 40) or epithelial cells (GM-CSF41) are ascribed crucial roles in host resistance based on the early mortality of knockout mice following infection. The gene discussed is TNF; the disease is infection.