TNF and tuberculosis: The progression of LTBI to active TB is determined by factors related to the bacteria (e.g., strain virulence, inoculum size, etc.), host (e.g., state of immune response, treatment with steroids, and biologic agents such as antibodies against tumor necrosis factor, solid organ or hematological transplantation, HIV infection, age), and environment (e.g., smoking, occupational exposure in health care workers).