Flow cytometry analysis of CD4+IFN-γ+ T-cells for the diagnosis of mycobacterium tuberculosis infection

Abstract

Background CD4+ cells expressing Interferon-γ (IFN-γ), following stimulation with specific mycobacterial antigens, identified with flow cytometry (FCM-CD4+IFN-γ+), is a new method for the diagnosis of Mycobacterium tuberculosis (MTB) infection. The aim of this study is to investigate the performance of FCM-CD4+IFN-γ+ in comparison with tuberculin skin test (TST) and Quantiferon TB Gold In-Tube (QFT-G-IT) in the diagnosis of latent MTB infection (LTBI), in close contacts and in patients with rheumatic diseases under treatment with anti-TNFa and other biologic agents. Methods TST, QFT-G-IT, and FCM-CD4+IFN-γ+ were performed in 56 immunocompetent close contacts and in 65 medically immunosuppressed patients under biologic treatment. Results In close contacts, 63% were FCM-CD4+IFN-γ+ ESAT-6(+), 70% FCM-CD4+IFN-γ+ PPD(+), 41% QFT-G-IT(+) and 57% TST(+). FCM-CD4+IFN-γ+ ESAT-6 was the only test that was strongly correlated to the exposure time to infection. In the immunosuppressed group, 49% were FCM-CD4+IFN-γ+ ESAT-6(+), 62% FCM-CD4+IFN-γ+ PPD(+), 4.6% QFT-G-IT(+), and 18% TST(+). Conclusion FCM-CD4+IFN-γ+ assays are more sensitive than QFT-G-IT and TST for the diagnosis of LTBI in close contacts and in immunosuppressed patients under anti-TNF-a treatment. FCM-CD4+IFN-γ+ is not affected by the chronic use of biologic agents.