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Free Content Relationship between IFN-γ and skin test responsiveness to Mycobacterium tuberculosis PPD in healthy, non-BCG-vaccinated young adults in Northern Malawi

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SETTING: Rural northern Malawi, where vaccination with BCG Glaxo (1077) provides protection against leprosy but not against pulmonary tuberculosis.

OBJECTIVE: To evaluate the patterns of responsiveness to purified protein derivative of Mycobacterium tuberculosis (PPD) in terms of delayed type hypersensitivity (DTH) and interferon-gamma (IFN-γ) production.

DESIGN: IFN-γ was measured in 6 day whole blood cultures diluted 1 in 10, stimulated with PPD RT48, and the results compared to the DTH response to PPD RT23. A total of 633 individuals aged 12 to 28 years, without prior BCG vaccination, were recruited.

RESULTS: Overall, 63% of subjects made a positive IFN-γ response (defined as >62 pg/ml), and 37% gave a DTH induration of >5 mm. A strong correlation between skin test and IFN-γ responses was observed, although with interesting exceptions: 13/270 individuals with zero DTH showed IFN-γ responses >500 pg/ml, and 7/53 individuals with >10 mm induration showed IFN-γ responses 62 pg/ml. The prevalence of skin test responsiveness increased with age, and was higher among older males than females; age-sex patterns were less clear for IFN-γ production.

CONCLUSION: The 6 day IFN-γ response to PPD correlates well with Mantoux skin test induration. The discordant individuals may represent important subsets in terms of protective immunity and risk of clinical tuberculosis.
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Keywords: M. tuberculosis; interferon-; skin test; whole blood assay

Document Type: Regular Paper

Affiliations: 1: Karonga Prevention Study, Chilumba, Malawi and Department of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK 2: Department of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK 3: Karonga Prevention Study, Chilumba, Malawi 4: Wellcome Trust Centre for Molecular Mechanisms in Disease, Addenbrookeƕs Hospital, Cambridge, UK 5: Karonga Prevention Study, Chilumba, Malawi and Department of Respiratory Medicine, University of Edinburgh Medical School, Edinburgh, UK

Publication date: July 1, 2001

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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 lung health world-wide.

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