Aberrant plasma IL-7 and soluble IL-7 receptor levels indicate impaired T-cell response to IL-7 in human tuberculosis

PLoS Pathog. 2017 Jun 5;13(6):e1006425. doi: 10.1371/journal.ppat.1006425. eCollection 2017 Jun.

Abstract

T-cell proliferation and generation of protective memory during chronic infections depend on Interleukin-7 (IL-7) availability and receptivity. Regulation of IL-7 receptor (IL-7R) expression and signalling are key for IL-7-modulated T-cell functions. Aberrant expression of soluble (s) and membrane-associated (m) IL-7R molecules is associated with development of autoimmunity and immune failure in acquired immune deficiency syndrome (AIDS) patients. Here we investigated the role of IL-7/IL-7R on T-cell immunity in human tuberculosis. We performed two independent case-control studies comparing tuberculosis patients and healthy contacts. This was combined with follow-up examinations for a subgroup of tuberculosis patients under therapy and recovery. Blood plasma and T cells were characterised for IL-7/sIL-7R and mIL-7R expression, respectively. IL-7-dependent T-cell functions were determined by analysing STAT5 phosphorylation, antigen-specific cytokine release and by analysing markers of T-cell exhaustion and inflammation. Tuberculosis patients had lower soluble IL-7R (p < 0.001) and higher IL-7 (p < 0.001) plasma concentrations as compared to healthy contacts. Both markers were largely independent and aberrant expression normalised during therapy and recovery. Furthermore, tuberculosis patients had lower levels of mIL-7R in T cells caused by post-transcriptional mechanisms. Functional in vitro tests indicated diminished IL-7-induced STAT5 phosphorylation and impaired IL-7-promoted cytokine release of Mycobacterium tuberculosis-specific CD4+ T cells from tuberculosis patients. Finally, we determined T-cell exhaustion markers PD-1 and SOCS3 and detected increased SOCS3 expression during therapy. Only moderate correlation of PD-1 and SOCS3 with IL-7 expression was observed. We conclude that diminished soluble IL-7R and increased IL-7 plasma concentrations, as well as decreased membrane-associated IL-7R expression in T cells, reflect impaired T-cell sensitivity to IL-7 in tuberculosis patients. These findings show similarities to pathognomonic features of impaired T-cell functions and immune failure described in AIDS patients.

MeSH terms

  • Adult
  • Aged
  • CD4-Positive T-Lymphocytes / immunology*
  • Case-Control Studies
  • Female
  • Humans
  • Interleukin-7 / blood*
  • Interleukin-7 / genetics
  • Interleukin-7 / immunology
  • Male
  • Middle Aged
  • Mycobacterium tuberculosis / genetics
  • Mycobacterium tuberculosis / physiology
  • Phosphorylation
  • Receptors, Interleukin-7 / blood*
  • Receptors, Interleukin-7 / genetics
  • Receptors, Interleukin-7 / immunology
  • STAT5 Transcription Factor / genetics
  • STAT5 Transcription Factor / immunology
  • Suppressor of Cytokine Signaling 3 Protein / genetics
  • Suppressor of Cytokine Signaling 3 Protein / immunology
  • Tuberculosis / immunology*
  • Tuberculosis / microbiology
  • Young Adult

Substances

  • Interleukin-7
  • Receptors, Interleukin-7
  • STAT5 Transcription Factor
  • Suppressor of Cytokine Signaling 3 Protein

Grants and funding

This study was supported by the German Research Foundation (DFG, JA 1479/5-1) and the German Leprosy and TB relief association (DAHW) project: TB Biomarkers to MJ. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.