Toll-like receptor control of glucocorticoid-induced apoptosis in human plasmacytoid predendritic cells (pDCs)

Blood. 2010 Nov 4;116(18):3389-97. doi: 10.1182/blood-2010-05-282913. Epub 2010 Jun 30.

Abstract

Microbial infection triggers the endogenous production of immunosuppressive glucocorticoid (GC) hormones and simultaneously activates innate immunity through toll-like receptors (TLRs). How innate immune cells integrate these 2 opposing signals in dictating immunity or tolerance to infection is not known. In this study, we show that human plasmacytoid predendritic cells (pDCs) were highly sensitive to GC-induced apoptosis. Strikingly, they were protected by microbial stimulation through TLR-7 and TLR-9, but not by microbial-independent stimuli, such as interleukin-3, granulocyte macrophage colony-stimulating factor, or CD40-ligand. This protection was dependent on TLR-induced autocrine tumor necrosis factor-α and interferon-α, which collectively increased the expression ratio between antiapoptotic genes (Bcl-2, Bcl-xL, BIRC3, CFLAR) versus proapoptotic genes (Caspase-8, BID, BAD, BAX). In particular, virus-induced Bcl-2 up-regulation was dependent on autocrine interferon-α. Using small interfering RNA technology, we demonstrated that Bcl-2 and CFLAR/c-flip were essential for TLR-induced protection of pDCs from GC-induced caspase-8-mediated apoptosis. Our results demonstrate a novel property of the TLR pathway in regulating the interface between GC and innate immunity and reveal a previously undescribed mechanism of GC resistance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis*
  • CASP8 and FADD-Like Apoptosis Regulating Protein / immunology
  • Cells, Cultured
  • Dendritic Cells / cytology
  • Dendritic Cells / immunology*
  • Dendritic Cells / microbiology
  • Glucocorticoids / immunology*
  • Humans
  • Interferon-alpha / immunology
  • Proto-Oncogene Proteins c-bcl-2 / immunology
  • Toll-Like Receptor 7 / immunology
  • Toll-Like Receptor 9 / immunology
  • Toll-Like Receptors / immunology*
  • Tumor Necrosis Factor-alpha / immunology

Substances

  • CASP8 and FADD-Like Apoptosis Regulating Protein
  • CFLAR protein, human
  • Glucocorticoids
  • Interferon-alpha
  • Proto-Oncogene Proteins c-bcl-2
  • Toll-Like Receptor 7
  • Toll-Like Receptor 9
  • Toll-Like Receptors
  • Tumor Necrosis Factor-alpha