IL-10–expressing T cells were detected in large numbers in the lung after 3 wk of infection and, in line with a previous study reporting enhanced susceptibility to M. tuberculosis infection in mice overexpressing IL-10 in the T cell compartment (27), we found that mice with specific deletion of Il10 in T cells were more resistant to M. tuberculosis infection than IL-10–competent mice. The gene discussed is IL10; the disease is infection.