Flowcytometric assessment of intracellular interferon-gamma production in human CD4+ve T-cells on mycobacterial antigen stimulation

Interferon-gamma (IFN-gamma) has been considered to be a critical protective immunomodulatory component against Mycobacterium tuberculosis (M. tb.) infection. In this study T-cell proliferation and IFN-gamma production upon stimulation with M. tb. were assessed in patients of pulmonary tuberculosis and healthy contacts. The studies mere based on lymphocyte transformation test and detection of intracellular IFN-gamma production by CD4 + ve T-cells by flowcytometry. Patients showed lower levels of proliferation, the stimulation index being in the range of 2.17 +/- 1.1 (mean +/- SD) compared to the contacts (SI = 4.59 +/- 1.6) (P < 0.01). The kinetics of intracellular induction of IFN-gamma on M. tb. stimulation showed a proportional increase in the CD4 + ve T-cell population. The increase was maximal between 96-120 h of culture, In healthy contacts the number of IFN-gamma expressing CD + ve T-cells increased to 2.5 to 41 x 10(4) cells/ml in M. tb. stimulated cultures compared to control cultures (0.1-15 x 10(4)). In contrast patients showed no/marginal increase in CD4 + ve T-cell population expressing intracellular IFN-gamma. Thus the lack of induction of IFN-gamma in CD4 + ve T-cells in patients could be a critical shortcoming in their ability to combat tubercle bacilli infection.