Tuberculosis (TB) is a major global health concern. One third of the world's population is infected with Mycobacterium tuberculosis. Two to 3 million people die every year of the disease with 8-10 million new cases per year. It is projected that there will be 90 million new cases and 30 million deaths over the next decade. For a disease, which we know to have existed since 2400 BC, our understanding of its pathogenesis is incomplete, especially in relation to the human immune response and the role of lymphocytes in particular.