Interferon γ in patients with HIV/AIDS and suspicion or latent tuberculosis infection.

Asian Pac J Trop Med. 2013 Feb;6(2):135-8.

García-Elorriaga G, Martínez-Velázquez M, Gaona-Flores V, del Rey-Pineda G, González-Bonilla C.

Unidad de Investigación en Inmunología e Infectología, Centro Médico Nacional La Raza, Instituto Mexicano del Seguro Social Mexico City, Mexico. gelorriaga@webtelmex.net.mx

Abstract

OBJECTIVE: To assess the usefulness of IGRA test (QuantiFERON(®)-Cell mediated immune) compared with the tuberculin skin test.

METHODS: A cross-sectional study was carried out in Mexico, 25 infected patients with HIV-AIDS and the suspicion or with latent tuberculous infection (LTBI) who were >18 years of age and without treatment for tuberculosis (TB), were enrolled in the study.

RESULTS: Median cluster of differentiation (CD4) count was 364 cells/μ L and median HIV viral load was 50 copies/mL. Overall, 20 patients (80%) had at least one positive diagnostic test for LTBI: four (16%) had a positive tuberculin skin test and 19 (76%), a positive QuantiFERON(®)-tuberculosis.

CONCLUSIONS: No agreement is found between the two diagnostic tests: k = -0.004, 95% confidence interval (-0.2219, 0.2210). Additional longitudinal studies among HIV-infected populations with high prevalence of TB are needed to further assess the usefulness of IGRAs in this patient population. Copyright © 2013 Hainan Medical College. Published by Elsevier B.V.

PMID: 23339916

 

Supplementary

The usual technique used to diagnose latent tuberculosis infection (LTBI) is the tuberculin skin test (TST), although its low specificity is a major problem since its proteins are not specific to Mycobacterium tuberculosis (MTB). In the past few years, new diagnostic methods have been researched and approved based on the in vitro quantification of the cell-mediated immune response, particularly the interferon gamma (IFN γ) release assay (IGRA) that detects IFN y release in response to specific MTB antigens.

IFN γ is a key molecule in tuberculosis (TB) control and its effects are crucial to the protective immune response against this organism. This cytokine, generated by CD4+, CD8+ and NK lymphocytes activates infected macrophages that in turn, release IL-1 and TNF-α limiting mycobacterial growth and multiplication.

Our results are of interest since very few such studies have been conducted in TB highly endemic countries, such as ours. However, it has its limitations and further research should be conducted in a longitudinal study with larger numbers of patients and including various degrees of immunodeficiency; moreover, this study used the first generation of the QuantiFERON-TB approved by the Food and Drug Administration (FDA) that detects IFN γ release in response to the purified protein derivative (PPD). It would thus be useful to use the second generation diagnostic test, known as QuantiFERON-TB Gold that unlike the first generation assay uses synthetic peptides mimicking more specific antigens such as the Early Secreted Antigenic Target-6 (ESAT-6) and Culture Filtrate Protein-10 (CFP-10). These two molecules are encoded in the RD-1 region of the MTB genome and significantly increase specificity when compared to PPD. These antigens are absent in M.bovis BCG and in most non-tuberculous mycobacteria (NTM) (except M. kansasii, M. marinum, M. szulgai). The third generation of this assay known as the QuantiFERON-TB Gold In Tube (QFT-GIT) is now commercially available and includes a third mycobacterial antigen, TB 7.7 and specifically designed vials in which the blood sample is collected.

Regardless, as of today and based on current knowledge, it appears that the IGRA may complement the TST, but not replace it.

García-Elorriaga-1

PPD = Purified protein derivative; TNFα = Tumor necrosis factor α; IL-8 = Interleukin 8.

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