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Gamma Interferon Responses Induced by a Panel of Recombinant and Purified Mycobacterial Antigens in Healthy, Non-Mycobacterium bovis BCG-Vaccinated Malawian Young Adults

Gillian F. Black,^1,2, Rosemary E. Weir,² Steven D. Chaguluka,¹ David Warndorff,^1,2 Amelia C. Crampin,^1,2 Lorren Mwaungulu,¹ Lifted Sichali,¹ Sian Floyd,² Lyn Bliss,² Elizabeth Jarman,^1, Linda Donovan,¹ Peter Andersen,³ Warwick Britton,⁴ Glyn Hewinson,⁵ Kris Huygen,⁶ Jens Paulsen,⁷ Mahavir Singh,⁷ Ross Prestidge,⁸ Paul E. M. Fine,² and Hazel M. Dockrell^2*

Karonga Prevention Study, Chilumba, Malawi,¹ Department of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London WC1E 7HT,² Central Veterinary Laboratories, Weybridge, United Kingdom,⁵ Statens Serum institut, Copenhagen, Denmark,³ Centenary Institute of Cancer Medicine and Cell Biology, Newtown, Sydney 2006, Australia,⁴ Pasteur Institute, Brussels, Belgium,⁶ GBF, 38124 Braunschweig, Germany,⁷ Genesis, Auckland, New Zealand⁸

Received 21 October 2002/ Returned for modification 27 January 2003/ Accepted 27 March 2003

We have previously shown that young adults living in a rural area of northern Malawi showed greater gamma interferon (IFN-) responses to purified protein derivatives (PPD) prepared from environmental mycobacteria than to PPD from Mycobacterium tuberculosis. In order to define the mycobacterial species to which individuals living in a rural African population have been exposed and sensitized, we tested T-cell recognition of recombinant and purified antigens from M. tuberculosis (38 kDa, MPT64, and ESAT-6), M. bovis (MPB70), M. bovis BCG (Ag85), and M. leprae (65 kDa, 35 kDa, and 18 kDa) in >600 non-M. bovis BCG-vaccinated young adults in the Karonga District of northern Malawi. IFN- was measured by enzyme-linked immunosorbent assay (ELISA) in day 6 supernatants of diluted whole-blood cultures. The recombinant M. leprae 35-kDa and 18-kDa and purified native M. bovis BCG Ag85 antigens induced the highest percentages of responders, though both leprosy and bovine tuberculosis are now rare in this population. The M. tuberculosis antigens ESAT-6 and MPT64 and the M. bovis antigen MPB70 induced the lowest percentages of responders. One of the subjects subsequently developed extrapulmonary tuberculosis; this individual had a 15-mm-diameter reaction to the Mantoux test and responded to M. tuberculosis PPD, Ag85, MPT64, and ESAT-6 but not to any of the leprosy antigens. We conclude that in this rural African population, exposure to M. tuberculosis or M. bovis is much less frequent than exposure to environmental mycobacteria such as M. avium, which have antigens homologous to the M. leprae 35-kDa and 18-kDa antigens. M. tuberculosis ESAT-6 showed the strongest association with the size of the Mantoux skin test induration, suggesting that among the three M. tuberculosis antigens tested it provided the best indication of exposure to, or infection with, M. tuberculosis.

Present address: Department of Medical Biochemistry, Stellenbosch Medical School, Tygerberg 7505, South Africa.

Present address: ALK-Abello A/S, DK-2970 Hoersholm, Denmark.

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