Mycobacteriulll tuberculosis and HIV - I arc known to interact with each other with anrnimpact on the immunological, virological/bacterial and clinical outcomes of bothrninfections. We aimed to evaluate the ill vitro and ill vivo immunolgical alterations in TBrnand HlV-1 co-infection. The study population consisted of 101 subjects: HIV- and HlV+rnindividuals with TB (HlV-TB+, n=29; HIV+TB+, n=31), individuals with HIV onlyrn(HlV+TB-, n=19), and healthy controls (HlV-TB-, n=22). Lymphoproliferative responsesrnwere evaluated in mitogen- or antigen-stimulated PBMCs by BrdU ELISA. Cytokinesrn(IFN-y, IL-lO, and IL-12) in cell culturc supell1atants of PBMCs, and plasmarnconcentrations of TNF-a and TNF-RII werc measured by sandwich ELISA. Plasma viralrnload was detelmined by nucleic acid sequence-based amplification; and C04+ T-cellsrnwere enumerated by FACScan. Results showed that C04+ cell counts (cells/mm3) werernsignificantly reduced in individuals with TB and/or HlV infections compared to thernhealthy controls. Patients co-infected with TB/HIV had a significantly elevated plasmarnviral load (loglO copies/ml) as compared to HIV+ without TB. Proliferative responsesrnwere reduced in TB+HlV- (1.36 and 0.58 to PHA and PPO, respectively), TB-HlV+ (1.17rnand 0.40) as well as those with TB+HlV+ (1.13 and 0.47) compared to healthy controlsrn(1.76 and 0.83). IFN-y production was significantly depressed in TB+HIV- (P