Human Host Defense and Cytokines in Mycobacterial Infectious Diseases: Interleukin‐18 Cannot Compensate for Genetic Defects in the Interleukin‐12 System

Abstract
SIR—Cell-mediated immunity plays a critical role in human host defense against intracellular bacteria, including mycobacteria and salmonellae [1, 2]. A key effector cytokine in cell-mediated immunity is the type 1 cytokine IFN-γ, which activates macrophages to promote the killing of intracellular microbes. IFN-γ is produced by T helper 1 lymphocytes and natural killer cells, and its production is controlled by IL-12, a cytokine that is secreted by infected macrophages and dendritic cells.