Cell-mediated immune response to tuberculosis antigens: comparison of skin testing and measurement of in vitro gamma interferon production in whole-blood culture.
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-gamma) 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 H(37)RV. Secretion of IFN-gamma (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-gamma 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.
Katial
R K
RK
Allergy-Immunology Department, Walter Reed Army Medical Center, 6900 Georgia Ave., Washington, D.C. 20307, USA. rohit.katial@amedd.army.mil
Hershey
J
J
Purohit-Seth
T
T
Belisle
J T
JT
Brennan
P J
PJ
Spencer
J S
JS
Engler
R J
RJ
D000328:Adult; D000942:Antigens, Bacterial / Q000276:immunology / Q000302:isolation & purification; D006801:Humans; D006968:Hypersensitivity, Delayed / Q000276:immunology*; D007111:Immunity, Cellular / Q000276:immunology; D066298:In Vitro Techniques; D007371:Interferon-gamma / Q000097:blood*; D008875:Middle Aged; D009162:Mycobacterium avium / Q000276:immunology; D009169:Mycobacterium tuberculosis / Q000276:immunology*; D014373:Tuberculin / Q000276:immunology*; D014374:Tuberculin Test; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000276:immunology
D000942:Antigens, Bacterial; D014373:Tuberculin; D007371:Interferon-gamma