T-SPOT.TB is an enzyme-linked immunospot assay performed on separated and counted peripheral blood mononuclear cells (PBMCs); it uses MTB specific antigens including early secreted antigenic target 6 (ESAT-6) and culture filtrate protein (CFP-10) peptides, and the result is reported as number of interferon-gamma producing T cells (spot-forming cells). The gene discussed is IFNG; the disease is tuberculosis.