Recently, a whole blood interferon-gamma assay has been introduced for the diagnosis of latent tuberculosis infection and active tuberculosis; this assay is based on a specific elevation in the interferon-gamma concentration that occurs as T cells respond to early-secreted antigenic target 6-kDa protein (ESAT-6) and culture filtrate protein 10 (CFP-10), both of which are specifically expressed by Mycobacterium tuberculosis but not by BCG strains. The gene discussed is IFNG; the disease is tuberculosis.