Background : Tuberculosis in an infectious disease which caused by Mycobacterium tuberculosis (M.tuberculosis) that infected numeruous organ espicially the lung. A person's immunity is very affecting for a person exposed to Pulmonary tuberculosis. T helper-1 cell (Th1) is very influential in immune system especially in interfering intracellular bacterial infection. One of the cytokine known produced by Th1 cell is interferon gamma (IFN-γ) which is important in eliminating M.tuberculosis. The aim of this study is to identify the association between level of IFN-γ and AFB positivity in Pulmonary tuberculosis patients in Medan. This is a case control study. The subjects of the study were 60 new cases of pulmonary tuberculosis with AFB sputum smear-positive that never received ATT consisting 20 cases AFB (+1), 20 cases AFB (+2) and 20 cases AFB (+3). Samples were plasma collected from the venous blood of pulmonary tuberculosis patients. The plasma then underwent laboratory assay with ELISA techniques. Independent t test was done with p<0.05 was considered significant.

Conclusion : level of IFN-γ in TB AFB (+1) is higher than TB AFB (+2) and (+3), with significant statistical result (p=0.001).