Impact of age and sex on mycobacterial immunity in an area of high tuberculosis incidence.
METHODS
The extent of immune reactivity measured by the tuberculin skin test (TST) and interferon-gamma (IFN-gamma) T-cell assays is usually not analysed.


OBJECTIVE
To determine the impact of age and sex on assay positivity and on the extent of reactivity of both TST and T-cell assays in young persons in an area of South Africa with high TB transmission.


RESULTS
Age had a strong impact on assay positivity for all seven immune phenotypes tested (P < 0.0007). Among positive responders, the extent of purified protein derivative (PPD) triggered IFN-gamma release (P < 0.003) was sensitive to age. ESAT-6 triggered IFN-gamma release (day 7, P = 0.03) and the frequency of PPD-specific IFN-gamma(+)CD4(+) (P = 0.03) and IFN-gamma(+)CD8(+) cells (P = 0.04) were weakly dependent on age. By contrast, the extent of TST induration was insensitive to age (P > 0.05), and sex had no significant impact on any phenotype measured (P > 0.05). The high proportion of positive responders in the 1-10 year age-group observed with long-term whole blood assays, but not with 3-day assays and TST, suggests that long-term whole blood assays may be confounded by bacille Calmette-Guérin vaccination in this age group.


CONCLUSIONS
There is a significant impact of age, but not sex, on different assays of immune reactivity in this high TB transmission setting.
Gallant
C J
CJ
Department of Human Genetics and Medicine, McGill University, McGill Centre for the Study of Host Resistance, Montreal, Canada.
Cobat
A
A
Simkin
L
L
Black
G F
GF
Stanley
K
K
Hughes
J
J
Doherty
T M
TM
Hanekom
W A
WA
Eley
B
B
Beyers
N
N
Jaïs
J-P
JP
van Helden
P
P
Abel
L
L
Alcaïs
A
A
Hoal
E G
EG
Schurr
E
E
D000293:Adolescent; D017677:Age Distribution; D000367:Age Factors; D000942:Antigens, Bacterial / Q000276:immunology*; D002648:Child; D002675:Child, Preschool; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007113:Immunity, Innate; D015994:Incidence; D007223:Infant; D007371:Interferon-gamma / Q000276:immunology; D008297:Male; D009169:Mycobacterium tuberculosis / Q000276:immunology* / Q000302:isolation & purification; D010641:Phenotype; D012189:Retrospective Studies; D017678:Sex Distribution; D012737:Sex Factors; D013019:South Africa / Q000453:epidemiology; D014374:Tuberculin Test; D014376:Tuberculosis / Q000453:epidemiology* / Q000276:immunology / Q000382:microbiology; D055815:Young Adult
D000942:Antigens, Bacterial; D007371:Interferon-gamma