Immune Responses to Mycobacterium Tuberculosis

This study, conducted at the University of Mali in the capital city of Bamako, will investigate how the body reacts to infection with Mycobacterium tuberculosis (MTB), the organism that causes tuberculosis. Tuberculosis is a major global health problem whose solution requires development of an effective vaccine. However, incomplete understanding of how immunity to MTB is acquired and measured limits vaccine development. This study will focus on certain immune system cells - CD4+ T cells - that appear to be very important in fighting tuberculosis.

Individuals 16 years of age and older who have or have not been exposed to either tuberculosis or HIV, or both, may be eligible for this study. Candidates will be screened with a medical history, physical examination, blood tests, review of medical records and laboratory tests, and, if medically indicated, a chest x-ray. Individuals whose medical records indicate a past history of tuberculosis or a positive test for exposure to tuberculosis will have a tuberculin skin test. For this test, a few drops of fluid are placed under the skin to see if the immune system reacts to the substance, indicating previous exposure to MTB.

Participants will come to the University of Mali 10 times over a 1-year period - 7 times within the first 3 months of the study and then once every 3 months until 1 year after enrollment. At each study visit, they will be asked about their medical history and will donate 75 milliliters (about 1/3 cup) of blood, totaling 830 mL over the entire year. More blood may be requested if the participant's immune system reacts strongly to MTB in laboratory tests. No more than 450 mL (2 cups) of blood would be collected every 6 weeks; this amount is the Red Cross limit for regular blood donations every 6 weeks.

The blood samples will be used for tests that measure the level of immunity to tuberculosis. Genetic tests may be performed on blood cells to help interpret special tests of immunity. Because HIV-infected people are included in the study, the findings may also provide information on how HIV renders vulnerability to opportunistic infections, including tuberculosis.