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