Tuberculin-specific T cells are reduced in active pulmonary tuberculosis compared to LTBI or status post BCG vaccination.

Functional characteristics of tuberculosis (TB)-specific CD4 T cells were studied in clinically active pulmonary TB (n = 21) and high TB exposure including LTBI (n = 17). Following tuberculin stimulation, activated CD4 T cells were identified by flow-cytometry (CD154 up-regulation, degranulation, interferon gamma [IFN-gamma], tumor necrosis factor alpha [TNF-alpha], and interleukin 2 [IL-2\ production). Interestingly, CD154 up-regulation accounted for similar to 80% of activated CD4 T cells in the active TB group but just 40% in the controls, whereas IFN-gamma accounted for only similar to 50% of activated cells in each group. The frequencies of CD4 T cells displaying at least 1 activation marker discriminated better between the groups than those displaying degranulation or IFN-gamma production alone.