High Frequencies of Caspase-3 Expressing Mycobacterium tuberculosis-Specific CD4+ T Cells Are Associated With Active Tuberculosis.

Toidi Adekambi,Stephanie Cagle,Chris C Ibegbu,Susan M Ray,Jyothi Rengarajan

doi:10.3389/fimmu.2018.01481

Abstract

Antigen-specific CD4+ T cell responses to Mycobacterium tuberculosis (Mtb) infection are important for host defense against tuberculosis (TB). However, Mtb-specific IFN-γ-producing T cells do not distinguish active tuberculosis (ATB) patients from individuals with asymptomatic latent Mtb infection (LTBI). We reasoned that the immune phenotype of Mtb-specific IFN-γ+CD4+ T cells could provide an indirect gauge of Mtb antigen load within individuals. We sought to identify immune markers in Mtb-specific IFN-γ+CD4+ T cells and hypothesized that expression of caspase-3 Mtb-specific CD4+ T cells would be associated with ATB. Using polychromatic flow cytometry, we evaluated the expression of caspase-3 in Mtb-specific CD4+ T cells from LTBI and ATB as well as from ATB patients undergoing anti-TB treatment. We found significantly higher frequencies of Mtb-specific caspase-3+IFN-γ+CD4+ T cells in ATB compared to LTBI. Caspase-3+IFN-γ+CD4+ T cells were also more activated compared to their caspase-3-negative counterparts. Furthermore, the frequencies of caspase-3+IFN-γ+CD4+ T cells decreased in response to anti-TB treatment. Our studies suggest that the frequencies of caspase-3-expressing antigen-specific CD4+ T cells may reflect mycobacterial burden in vivo and may be useful for distinguishing Mtb infection status along with other host biomarkers.

Highlights

Tuberculosis (TB) is one of the world’s major causes of illness and mortality [1] with about 10 million new cases and 2 million deaths occurring each year
Gating on live lymphocytes (Figure S1 in Supplementary Material), we evaluated the expression of active caspase-3 on IFN-γ+CD4+ T cells in active TB (ATB) patients and healthy subjects with latent Mtb infection (LTBI) (Table 1), after stimulating peripheral blood mononuclear cells (PBMCs) with Mycobacterium tuberculosis (Mtb)-cell wall (CW) antigens and ESAT6-CFP10 peptides pools
We found that caspase-3+IFN-γ+CD4+ T cells express higher levels of CD38 (75 vs 55%, p = 0.019), HLA-DR (98 vs 80%), and Ki-67 (40 vs 20%) compared to caspase-3−IFN-γ+CD4+ T cells (Figure 2) upon stimulation with Mtb-CW antigens

Summary

Introduction

Tuberculosis (TB) is one of the world’s major causes of illness and mortality [1] with about 10 million new cases and 2 million deaths occurring each year. Several studies have shown that the majority of individuals infected with Mtb mount robust antigen-specific CD4+ T cell responses involving T helper 1 (Th1) cytokines, such as IFN-γ and TNF-α, which are critical for activating macrophages and containing bacteria in the lung. We showed that compared to individuals with LTBI, PBMCs from ATB patients harbored significantly higher frequencies of Mtb-specific IFN-γ+CD4+ T cells expressing immune activation markers CD38 and HLA-DR and the intracellular proliferation marker Ki-67 [7]. These markers accurately identified ATB patients and correlated with response to anti-TB treatment [7]. Since ATB patients have higher frequencies of activated Mtb-specific CD4+ T cells compared to LTBI, we hypothesized that ATB would harbor higher frequencies of Mtb-specific CD4+ T cells expressing active caspase-3

Methods

Results

Conclusion