Tuberculosis (TB) causes an estimated 2 million deaths every year globally. The protective efficacy of bacille Calmette-Guerin (BCG) varies from zero to 80% in different population, and efforts to replace BCG has not been successful. The main reason is la ck of complete understanding on protective immune mechanisms. It is generally believed that T cell immunity is critical during mycobacterial infections. But the role of specific antibody responses has been ignored due to classical experiments that lacked standard protoccols and the Th1/Th2 paradigm that assigns a distinct division of labour for Th1 and Th2 cells. In addition to major descrepancies in the Th1 and Th2 model, a substantial body of data indicate that there is a synergy and mutual interdepende nce betwen Th1 and Th2 responses. Studies in B cell deficient and SCID mice indicate that specific antibodies have essential protective role during infections with intracellular pathogens, including Mtb.Cohorts of human TB cases (confirmed by sputum sme ar microscopy and culture), and thier contacts (HHCs), and community controls (CCs) will be selected based on clinical, X-ray, sputum, and IGRA tests in an endemic setting. Immune profile of TB patients will be determined before treatment, and six and 12 months after treatment. Immune profile of HHCs, and CCs will be determined upon entry into th study , and at 12 month intervals for at least two years. Blood will be collected and separated into cells and serum. Cytokine profile will be determined using cytokine ELISA and RT-PCR and antibody isotypes using ELISA. Appropriate statistical model will be used to determine corelates of immunity.