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

Abstract

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 γ [IFN-γ], tumor necrosis factor α [TNF-α], and interleukin 2 [IL-2\ production). Interestingly, CD154 up-regulation accounted for ∼80% of activated CD4 T cells in the active TB group but just 40% in the controls, whereas IFN-γ accounted for only ∼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-γ production alone.

Figure 1.

Detection of tuberculin-specific CD4 T cell responses. Cells were stimulated overnight with tuberculin or SEB. Unstimulated samples were run as controls. Activation was detected by CD154-up-regulation, degranulation (not shown), IFN-γ, TNF-α, and IL-2 production. SEB response size varied strongly between individuals and was not correlated with tuberculin response size. Percentages are indicated in quadrants, axes show log fluorescence intensity, CD4 T cells are displayed.

Figure 2.

Frequencies of activated CD4 T cells are higher in apTB than in hE, activation markers differ between groups. A, ROC-curves display sensitivity vs. specificity for discriminating apTB and hE by all tuberculin-induced activation markers combined and each activation marker alone. B, Bars (medians/95% confidence interval [CI]) indicate the frequencies of activated CD4 T cells per each activation marker alone. C, Bars (medians/95% CI) show proportions of activation marker positive cells among all activated cells. CD154 up-regulation was the most dominant single activation marker of tuberculin-specific T cells in apTB. D, Proportions of CD154, TNF-α (axes) and IFN-γ positive cells (bubble size) among all activated CD4 T cells are plotted against each other. The dotted line indicates an apparent division between hE and apTB. (“n.k.e”. = no known exposure to TB). Significant differences in B and C are indicated (Mann-Whitney U test).

Figure 2.

Frequencies of activated CD4 T cells are higher in apTB than in hE, activation markers differ between groups. A, ROC-curves display sensitivity vs. specificity for discriminating apTB and hE by all tuberculin-induced activation markers combined and each activation marker alone. B, Bars (medians/95% confidence interval [CI]) indicate the frequencies of activated CD4 T cells per each activation marker alone. C, Bars (medians/95% CI) show proportions of activation marker positive cells among all activated cells. CD154 up-regulation was the most dominant single activation marker of tuberculin-specific T cells in apTB. D, Proportions of CD154, TNF-α (axes) and IFN-γ positive cells (bubble size) among all activated CD4 T cells are plotted against each other. The dotted line indicates an apparent division between hE and apTB. (“n.k.e”. = no known exposure to TB). Significant differences in B and C are indicated (Mann-Whitney U test).