Active Tuberculosis Is Characterized by Highly Differentiated Effector Memory Th1 Cells

Area of Science:

• Immunology
• Molecular Biology
• Infectious Diseases

Background:

• Current diagnostics for latent Mycobacterium tuberculosis infection (LTBI) cannot distinguish it from active tuberculosis (TB) or predict disease progression.
• Existing assays measure single parameters like IFN-γ protein release after prolonged T cell stimulation, failing to capture dynamic immune responses.

Purpose of the Study:

• To develop and evaluate a novel, semi-automated RNA flow cytometry assay for differentiating LTBI from active TB.
• To identify immunological differences in T cell responses between LTBI and active TB stages.

Main Methods:

• Analysis of antigen-induced Th1 cytokine mRNA (IFNG, TNFA) expression in CD4+ T cells after short (2- and 6-h) ex vivo stimulation.
• Immunophenotyping of memory T cells, including assessment of CD27 and PD-1 expression.

Main Results:

• Antigen stimulation rapidly induced IFNG and TNFA mRNA in CD4+ T cells within 2 hours.
• Active TB showed a higher frequency of IFNG- and TNFA-expressing CD4+ T cells (Th1 cells) compared to LTBI.
• Active TB exhibited increased ratios of effector memory to central memory Th1 cells, linked to T cell differentiation (CD27 loss) but not exhaustion (PD-1 abundance).

Conclusions:

• Single-cell, mRNA-based measurements offer a sensitive approach to detect quantitative, time-dependent differences in T cell function between LTBI and active TB.
• The novel assay may improve the diagnosis of active TB and the prediction of LTBI progression.
• Identifying distinct T cell phenotypes associated with active TB could inform therapeutic strategies.