[Pathophysiology and immunology of tuberculosis]

Only isolated bacilli are capable of reaching the pulmonary alveoli. Draining towards the lymphatic glanglia which corresponds to the infected pulmonary segment or transported by alveolar macrophages after being phagocytosed, these bacteria liberate molecules (antigens) presented to T lymphocytes. After clonal expansion, specific lymphocytes migrate out of the lymph nodes. From the initial area, other areas are infected and these specific lymphocytes lead to a local inflammatory reaction which is very rich in cells, in particular in activated monocytes and macrophages. The inflammatory granuloma or "tubercle" leads to control of the infection in the majority of cases. The inverse of this is that in five or ten per cent of cases a part of this granuloma is necrosed and caseus and leads to (or accompanies) an intense bacterial multiplication. At this stage with the formation of the cavity numerous bacilli may seed other regions of the lung or infect other people. The immune response in which T lymphocytes play a fundamental role thus permit at the same time the control of infection and the establishment of a lesion assuring the perpetuation of the species of Mycobacterium tuberculosis by contaminating new subjects. The respective roles of the different types of T lymphocyte and of liberated lymphokines remains to be determined. Also the principle antigens of the bacillus need to be characterised. The "dominant" antigens are probably liberated by bacteria during their growth phase.