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Clinical and Diagnostic Laboratory Immunology, March 2001, p. 339-345, Vol. 8, No. 2
Allergy-Immunology Department, Walter Reed
Army Medical Center, Washington, D.C.,1 and
Department of Microbiology, Colorado State University, Fort
Collins, Colorado2
Received 7 August 2000/Returned for modification 19 October
2000/Accepted 8 December 2000
Although delayed-type hypersensitivity skin testing with tuberculin
purified protein derivative (PPD) is the standard for tuberculosis
screening, its variability suggests the need for a more sensitive,
noninvasive test. An in vitro whole-blood assay has been proposed as an
alternative. Using health care worker volunteers, we confirmed the
correlation between PPD skin test (PPD-ST) results (positive,
induration of >15 mm) and a standardized gamma interferon (IFN-
1071-412X/01/$04.00+0 DOI: 10.1128/CDLI.8.2.339-345.2001
Cell-Mediated Immune Response to Tuberculosis
Antigens: Comparison of Skin Testing and Measurement of In Vitro Gamma
Interferon Production in Whole-Blood Culture
)
assay, QuantiFERON-TB (Q-IFN), manufactured by CSL Biosciences in
Australia, and we evaluated Mycobacterium tuberculosis
culture subfractions as potential substitutes for PPD. Twenty healthy
volunteers with positive PPD-ST results and 20 PPD-ST-negative controls
were enrolled. Whole blood was cultured with human PPD antigens
(HuPPD), Mycobacterium avium complex (MAC) PPD,
phytohemagglutinin (PHA), and four M. tuberculosis culture subfractions: low-molecular-weight culture, filtrate, culture filtrate
without lipoarabinomannan, soluble cell wall proteins, and cytosolic
proteins, all developed from M. tuberculosis strain H37RV. Secretion of IFN-
(expressed as international
units per milliliter) was measured by an enzyme immunoassay. The PPD or subculture fraction response as a percentage of the PHA response was
used to determine positivity. Sixteen of 20 PPD-ST-positive individuals
were classified as M. tuberculosis positive by Q-IFN, and 1 was classified as MAC positive. Sixteen of 20 PPD-ST-negative individuals were M. tuberculosis negative by Q-IFN, 2 were
MAC positive, and 2 were M. tuberculosis positive. The
tuberculosis culture subfractions stimulated IFN-
production in
PPD-ST-positive volunteers, and significant differences could be seen
between the two PPD-ST groups with all subfractions except soluble cell wall protein; however, the response was variable and no better than the
Q-IFN PPD. The agreement between the Q-IFN test and the PPD-ST was good
(Cohen's kappa = 0.73). The Q-IFN assay can be a useful tool in
further studies of immune responses to M. tuberculosis antigens.
*
Corresponding author. Mailing address: Walter Reed Army
Medical Center, Allergy-Immunology Clinic, 6900 Georgia Ave.,
Washington, DC 20307. Phone: (202) 782-8085. Fax: (202) 782-7093. E-mail: rohit.katial{at}amedd.army.mil.
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