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Free Content Impact of age and sex on mycobacterial immunity in an area of high tuberculosis incidence

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SETTING: The extent of immune reactivity measured by the tuberculin skin test (TST) and interferon-gamma (IFN-γ) 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-γ release (P < 0.003) was sensitive to age. ESAT-6 triggered IFN-γ release (day 7, P = 0.03) and the frequency of PPD-specific IFN-γ+CD4+ (P = 0.03) and IFN-γ+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.

CONCLUSION: There is a significant impact of age, but not sex, on different assays of immune reactivity in this high TB transmission setting.
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Keywords: IFN-γ release assays; TST; covariates; tuberculosis

Document Type: Regular Paper

Affiliations: 1: McGill Centre for the Study of Host Resistance & Departments of Human Genetics and Medicine, McGill University, Montreal, Canada 2: South African Vaccine Initiative, Institute of Infectious Diseases and Molecular Medicine, Health Sciences Faculty, University of Cape Town, Cape Town, South Africa 3: Department of Infectious Disease Immunology, Statens Serum Institute, Copenhagen, Denmark 4: Paediatric Infectious Diseases Unit, School of Child and Adolescent Health, Red Cross Children's Hospital, University of Cape Town, Cape Town, South Africa 5: Desmond Tutu TB Centre, Department of Paediatrics and Child Health, Faculty of Health Sciences, Stellenbosch University, Tygerberg, South Africa 6: Faculté de Médecine Necker, Université de Paris Descartes, Paris, France

Publication date: 2010-08-01

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  • The International Journal of Tuberculosis and Lung Disease publishes articles on all aspects of lung health, including public health-related issues such as training programmes, cost-benefit analysis, legislation, epidemiology, intervention studies and health systems research. The IJTLD is dedicated to the continuing education of physicians and health personnel and the dissemination of information on tuberculosis and lung health world-wide.

    Certain IJTLD articles are selected for translation into French, Spanish, Chinese or Russian. They are available on the Union website

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