Screening of Tuberculosis by Interferon-gamma Assay Before Biologic Therapy for Rheumatoid Arthritis

Infection with Mycobacterium tuberculosis (M. tuberculosis) is a critical complication in anti-TNF therapies. In 141 BCG vaccinated healthy individuals and 71 rheumatoid arthritis (RA) patients as screening before anti-TNF therapies, M. tuberculosis specific immune responses were evaluated by tuberculin skin test (TST) and enzyme-linked immunospot assay (ELISPOT), which detected antigen specific IFN-gamma secreting cells in peripheral blood mononuclear cells simulated with either purified protein derivative (PPD), early secretory antigen target 6 (ESAT-6) or culture filtrate protein 10 (CFP-10). Induration over 5 mm in TST was found in 87.9% of controls and 21.4% of RA patients. Erythema size in TST was significantly suppressed in RA patients, especially those receiving prednisolone (PSL), whereas the PPD specific IFN-gamma secretion was less attenuated. Significant responses to either ESAT-6 or CFP-10 in ELISPOT were detected in 14.1% of RA patients including those having positive TST, while the ELISPOT assay was negative in all healthy individuals and 73.3% of RA patients having positive TST. Of ELISPOT positive RA patients, mean dosage of PSL was 4.58 mg and 1.25 mg in TST negative and positive patients, respectively. Thus, ELISPOT is useful for screening of tuberculosis in RA patients, even in those receiving corticosteroids.