Ligation of TLR9 induced on human IL-10-secreting Tregs by 1alpha,25-dihydroxyvitamin D3 abrogates regulatory function

J Clin Invest. 2009 Feb;119(2):387-98. doi: 10.1172/JCI32354. Epub 2009 Jan 12.


Signaling through the TLR family of molecular pattern recognition receptors has been implicated in the induction of innate and adaptive immune responses. A role for TLR signaling in the maintenance and/or regulation of Treg function has been proposed, however its functional relevance remains unclear. Here we have shown that TLR9 is highly expressed by human Treg secreting the antiinflammatory cytokine IL-10 induced following stimulation of blood and tissue CD3+ T cells in the presence of 1alpha,25-dihydroxyvitamin D3 (1alpha25VitD3), the active form of Vitamin D, with or without the glucocorticoid dexamethasone. By contrast, TLR9 was not highly expressed by naturally occurring CD4+CD25+ Treg or by Th1 and Th2 effector cells. Induction of TLR9, but not other TLRs, was IL-10 dependent and primarily regulated by 1alpha25VitD3 in vitro. Furthermore, ingestion of calcitriol (1alpha25VitD3) by human volunteers led to an increase of both IL-10 and TLR9 expression by CD3+CD4+ T cells analyzed directly ex vivo. Stimulation of 1alpha25VitD3-induced IL-10-secreting Treg with TLR9 agonists, CpG oligonucleotides, resulted in decreased IL-10 and IFN-gamma synthesis and a concurrent loss of regulatory function, but, unexpectedly, increased IL-4 synthesis. We therefore suggest that TLR9 could be used to monitor and potentially modulate the function of 1alpha25VitD3-induced IL-10-secreting Treg in vivo, and that this has implications in cancer therapy and vaccine design.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Calcitriol / pharmacology*
  • Dexamethasone / pharmacology
  • Humans
  • Interleukin-10 / biosynthesis*
  • Male
  • Middle Aged
  • Oligodeoxyribonucleotides / pharmacology
  • RNA, Messenger / analysis
  • Receptors, Calcitriol / physiology
  • T-Lymphocytes, Regulatory / drug effects
  • T-Lymphocytes, Regulatory / physiology*
  • Toll-Like Receptor 9 / genetics
  • Toll-Like Receptor 9 / physiology*


  • CPG-oligonucleotide
  • Oligodeoxyribonucleotides
  • RNA, Messenger
  • Receptors, Calcitriol
  • TLR9 protein, human
  • Toll-Like Receptor 9
  • Interleukin-10
  • Dexamethasone
  • Calcitriol