1) Pulmonary tuberculosis is caused by Mycobacterium tuberculosis and can be spread through infective droplets. It was an important cause of death before antibiotics but is rising again due to AIDS and drug resistance. 2) M. tuberculosis avoids being killed by macrophages and induces delayed hypersensitivity. This allows it to reside in phagosomes and avoid acidification, enabling it to multiply. 3) Primary tuberculosis occurs with initial exposure and may cause localized lesions or progressive disease. Secondary tuberculosis results from reactivation and causes more extensive tissue damage and necrosis. Complications include cavities, hemorrhage, and fistula formation.