Tuberculin skin test and in vitro assays provide complementary measures of antimycobacterial immunity in children and adolescents.
BACKGROUND
Although many studies have compared in vitro TB diagnostic tests with the venerable tuberculin skin test (TST), there is little understanding of the quantitative relationship between critical measures of antimycobacterial immunity used to detect TB infection. We, therefore, decided to determine the degree of redundancy between quantitative read-outs of in vivo and in vitro assays of antimycobacterial immunity.


METHODS
We enrolled 475 healthy HIV-negative children and young adults living in a hyperendemic area of TB. We measured in vivo TST responses, and a 1:10 diluted 3- or 7-day whole-blood assay was used to determine the in vitro antigen-specific interferon (IFN)-gamma cytokine release. The frequency of antigen-specific IFN-gamma(+)CD4(+) and IFN-gamma(+)CD8(+) cells was tested using intracellular cytokine staining after 1 day incubation.


RESULTS
In vivo TST responses segregated into two well-separated groups with either no measurable response (TST induration < 5 mm; n = 164) or a normally distributed group with TST indurations > or = 5 mm with peak at 15 mm (n = 260). In vitro assays provided a less pronounced separation of responders and nonresponders. Correlation analysis of responses among persons with TST > or = 5 mm demonstrated that extent of TST response was poorly correlated with IFN-gamma release (coefficients of correlation rho = 0.17-0.22) and frequency of IFN-gamma(+)CD4(+)/CD8(+) cells (rho = 0.05-0.17) across three stimulating antigens (Mycobacterium bovis bacillus Calmette-Guérin, purified protein derivative, early-secreted antigenic target-6).


CONCLUSIONS
We conclude that in vivo and in vitro assays are nonredundant, complementary measures of antimycobacterial immunity. Both TST and in vitro assays provided valuable information about antimycobacterial immunity and by inference latent TB in the studied high-incidence TB settings.
Gallant
Caroline J
CJ
Montreal General Hospital Research Institute, 1650 Cedar Ave, Room L11-521, Montreal, QC, H3G 1A4, Canada.
Cobat
Aurelie
A
Simkin
Leah
L
Black
Gillian F
GF
Stanley
Kim
K
Hughes
Jane
J
Doherty
T Mark
TM
Hanekom
Willem A
WA
Eley
Brian
B
Beyers
Nulda
N
Jaïs
Jean-Philippe
JP
van Helden
Paul
P
Abel
Laurent
L
Alcaïs
Alexandre
A
Hoal
Eileen G
EG
Schurr
Erwin
E
D000293:Adolescent; D000907:Antibodies, Bacterial / Q000097:blood; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology; D002452:Cell Count; D002648:Child; D019937:Diagnostic Techniques and Procedures; D005260:Female; D006801:Humans; D007109:Immunity; D066298:In Vitro Techniques; D007371:Interferon-gamma / Q000097:blood*; D008297:Male; D009169:Mycobacterium tuberculosis / Q000276:immunology*; D013019:South Africa; D014374:Tuberculin Test; D014376:Tuberculosis / Q000097:blood / Q000175:diagnosis / Q000276:immunology*
D000907:Antibodies, Bacterial; D007371:Interferon-gamma