Extracellular Release of CD11b by TLR9 Stimulation in Macrophages

PLoS One. 2016 Mar 8;11(3):e0150677. doi: 10.1371/journal.pone.0150677. eCollection 2016.

Abstract

CpG-DNA upregulates the expression of pro-inflammatory cytokines, chemokines and cell surface markers. Investigators have shown that CD11b (integrin αM) regulates TLR-triggered inflammatory responses in the macrophages and dendritic cells. Therefore, we aimed to identify the effects of CpG-DNA on the expression of CD11b in macrophages. There was no significant change in surface expression of CD11b after CpG-DNA stimulation. However, CD11b was released into culture supernatants after stimulation with phosphorothioate-backbone modified CpG-DNA such as PS-ODN CpG-DNA 1826(S). In contrast, MB-ODN 4531 and non-CpG-DNA control (regardless of backbone type and liposome-encapsulation) failed to induce release of CD11b. Therefore, the context of the CpG-DNA sequence and phosphorothioate backbone modification may regulate the effects of CpG-DNA on CD11b release. Based on inhibitor studies, CD11b release is mediated by p38 MAP kinase activation, but not by the PI3K and NF-κB activation. CD11b release is mediated by lysosomal degradation and by vacuolar acidification in response to CpG-DNA stimulation. The amount of CD11b in the exosome precipitant was significantly increased by CpG-DNA stimulation in vivo and in vitro depending on TLR9. Our observations perhaps give more insight into understanding of the mechanisms involved in CpG-DNA-induced immunomodulation in the innate immunity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • CD11b Antigen / metabolism*
  • Cell Line
  • Exosomes / metabolism
  • Extracellular Space / metabolism
  • Lysosomes / metabolism
  • Macrophages / drug effects
  • Macrophages / metabolism*
  • Mice
  • Oligodeoxyribonucleotides / pharmacology
  • Protein Kinase Inhibitors / pharmacology
  • Toll-Like Receptor 9 / agonists
  • Toll-Like Receptor 9 / metabolism*
  • p38 Mitogen-Activated Protein Kinases / antagonists & inhibitors

Substances

  • CD11b Antigen
  • Oligodeoxyribonucleotides
  • Protein Kinase Inhibitors
  • Toll-Like Receptor 9
  • p38 Mitogen-Activated Protein Kinases

Grants and funding

This research was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning in the Republic of Korea (NRF-2013R1A6A3A01061155, 2013R1A2A2A03067981, 2014M3C1A3051473, 2014M3A9D5A01073841, 2015R1A2A2A01007209), and a grant from the Hallym Research Fund (HRF-201505-012). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.