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Toll-like receptor 2 on inflammatory monocytes induces type I interferon in response to viral but not bacterial ligands.

Barbalat R, Lau L, Locksley RM, Barton GM - Nat. Immunol. (2009)

Bottom Line: The relevance of this recognition for antiviral immunity remains largely unexplained.TLR2-dependent induction of type I interferon occurred only in response to viral ligands, which indicates that TLR2 is able to discriminate between pathogen classes.Thus, the innate immune system can detect certain non-nucleic acid features of viruses and links this recognition to the induction of specific antiviral genes.

View Article: PubMed Central - PubMed

Affiliation: Division of Immunology and Pathogenesis, Department of Molecular & Cell Biology, University of California, Berkeley, California, USA.

ABSTRACT
Despite the paradigm that the innate immune system uses nucleic acid-specific receptors to detect viruses because of a lack of other conserved features, many viruses are recognized by Toll-like receptor 2 (TLR2) and TLR4. The relevance of this recognition for antiviral immunity remains largely unexplained. Here we report that TLR2 activation by viruses led to the production of type I interferon. TLR2-dependent induction of type I interferon occurred only in response to viral ligands, which indicates that TLR2 is able to discriminate between pathogen classes. We demonstrate that this specialized response was mediated by Ly6C(hi) inflammatory monocytes. Thus, the innate immune system can detect certain non-nucleic acid features of viruses and links this recognition to the induction of specific antiviral genes.

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Ly6Chigh inflammatory monocytes produce IFNβ in response to vaccinia virusa) Bone marrow or splenocytes from MOB mice were stimulated with CpG or vaccinia virus (VV) for 20 hours, stained with antibodies against B220 or CD11c, and analyzed by flow cytometry. Comparisons between YFP-gated cells (orange line) versus total ungated cells (shaded) are shown. b) Cells were treated as in (a) but stained with antibodies against Ly6C, CD11b, or Ly6G. Comparisons between YFP-gated cells (orange line) versus total ungated cells (shaded) are shown. c) TLR2 is expressed on inflammatory monocytes. Bone marrow or splenocytes from C57BL/6 or TLR2-deficient mice were stained with antibodies specific for CD11b, Ly6C, and TLR2. d) TLR2 on inflammatory monocytes mediates type I IFN production in response to vaccinia virus. Bone marrow cells from MOB mice were cultured in the presence or absence of an anti-TLR2 blocking monoclonal antibody and stimulated as indicated. The percentage of YFP+ cells was determined by flow cytometry. e) Purified inflammatory monocytes are sufficient to produce type I IFN when stimulated with vaccinia virus. Bone marrow cells from C57BL/6 or TLR2-KO mice were sorted based on CD11b and Ly6C as shown. The plots shown have excluded B220+ and CD11c+ cells. Post-sort populations are shown and the percentage of inflammatory monocytes is indicated. The positive and negative populations were stimulated as indicated, and type I IFN production was measured after 24 hours by bioassay. All data are representative of at least 3 experiments.
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Figure 5: Ly6Chigh inflammatory monocytes produce IFNβ in response to vaccinia virusa) Bone marrow or splenocytes from MOB mice were stimulated with CpG or vaccinia virus (VV) for 20 hours, stained with antibodies against B220 or CD11c, and analyzed by flow cytometry. Comparisons between YFP-gated cells (orange line) versus total ungated cells (shaded) are shown. b) Cells were treated as in (a) but stained with antibodies against Ly6C, CD11b, or Ly6G. Comparisons between YFP-gated cells (orange line) versus total ungated cells (shaded) are shown. c) TLR2 is expressed on inflammatory monocytes. Bone marrow or splenocytes from C57BL/6 or TLR2-deficient mice were stained with antibodies specific for CD11b, Ly6C, and TLR2. d) TLR2 on inflammatory monocytes mediates type I IFN production in response to vaccinia virus. Bone marrow cells from MOB mice were cultured in the presence or absence of an anti-TLR2 blocking monoclonal antibody and stimulated as indicated. The percentage of YFP+ cells was determined by flow cytometry. e) Purified inflammatory monocytes are sufficient to produce type I IFN when stimulated with vaccinia virus. Bone marrow cells from C57BL/6 or TLR2-KO mice were sorted based on CD11b and Ly6C as shown. The plots shown have excluded B220+ and CD11c+ cells. Post-sort populations are shown and the percentage of inflammatory monocytes is indicated. The positive and negative populations were stimulated as indicated, and type I IFN production was measured after 24 hours by bioassay. All data are representative of at least 3 experiments.

Mentions: Although the lack of CD11c expression suggested that pDCs were not responsible for the TLR2-dependent type I IFN production, we addressed this possibility directly using MOB mice. We compared the responding cells (YFP+) in bone marrow and spleen stimulated with vaccinia virus or CpG oligos. CpG oligos induce TLR9-dependent type I IFN production by pDCs, and the YFP+ cells in these cultures were B220+CD11c+, a surface phenotype consistent with that of pDCs (Fig. 5a). In contrast, the cells responding to vaccinia virus were B220- and had lower surface levels of CD11c (Fig. 5a). These distinct surface phenotypes clearly demonstrate that different cell types are responding to vaccinia virus and CpG oligos.


Toll-like receptor 2 on inflammatory monocytes induces type I interferon in response to viral but not bacterial ligands.

Barbalat R, Lau L, Locksley RM, Barton GM - Nat. Immunol. (2009)

Ly6Chigh inflammatory monocytes produce IFNβ in response to vaccinia virusa) Bone marrow or splenocytes from MOB mice were stimulated with CpG or vaccinia virus (VV) for 20 hours, stained with antibodies against B220 or CD11c, and analyzed by flow cytometry. Comparisons between YFP-gated cells (orange line) versus total ungated cells (shaded) are shown. b) Cells were treated as in (a) but stained with antibodies against Ly6C, CD11b, or Ly6G. Comparisons between YFP-gated cells (orange line) versus total ungated cells (shaded) are shown. c) TLR2 is expressed on inflammatory monocytes. Bone marrow or splenocytes from C57BL/6 or TLR2-deficient mice were stained with antibodies specific for CD11b, Ly6C, and TLR2. d) TLR2 on inflammatory monocytes mediates type I IFN production in response to vaccinia virus. Bone marrow cells from MOB mice were cultured in the presence or absence of an anti-TLR2 blocking monoclonal antibody and stimulated as indicated. The percentage of YFP+ cells was determined by flow cytometry. e) Purified inflammatory monocytes are sufficient to produce type I IFN when stimulated with vaccinia virus. Bone marrow cells from C57BL/6 or TLR2-KO mice were sorted based on CD11b and Ly6C as shown. The plots shown have excluded B220+ and CD11c+ cells. Post-sort populations are shown and the percentage of inflammatory monocytes is indicated. The positive and negative populations were stimulated as indicated, and type I IFN production was measured after 24 hours by bioassay. All data are representative of at least 3 experiments.
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Figure 5: Ly6Chigh inflammatory monocytes produce IFNβ in response to vaccinia virusa) Bone marrow or splenocytes from MOB mice were stimulated with CpG or vaccinia virus (VV) for 20 hours, stained with antibodies against B220 or CD11c, and analyzed by flow cytometry. Comparisons between YFP-gated cells (orange line) versus total ungated cells (shaded) are shown. b) Cells were treated as in (a) but stained with antibodies against Ly6C, CD11b, or Ly6G. Comparisons between YFP-gated cells (orange line) versus total ungated cells (shaded) are shown. c) TLR2 is expressed on inflammatory monocytes. Bone marrow or splenocytes from C57BL/6 or TLR2-deficient mice were stained with antibodies specific for CD11b, Ly6C, and TLR2. d) TLR2 on inflammatory monocytes mediates type I IFN production in response to vaccinia virus. Bone marrow cells from MOB mice were cultured in the presence or absence of an anti-TLR2 blocking monoclonal antibody and stimulated as indicated. The percentage of YFP+ cells was determined by flow cytometry. e) Purified inflammatory monocytes are sufficient to produce type I IFN when stimulated with vaccinia virus. Bone marrow cells from C57BL/6 or TLR2-KO mice were sorted based on CD11b and Ly6C as shown. The plots shown have excluded B220+ and CD11c+ cells. Post-sort populations are shown and the percentage of inflammatory monocytes is indicated. The positive and negative populations were stimulated as indicated, and type I IFN production was measured after 24 hours by bioassay. All data are representative of at least 3 experiments.
Mentions: Although the lack of CD11c expression suggested that pDCs were not responsible for the TLR2-dependent type I IFN production, we addressed this possibility directly using MOB mice. We compared the responding cells (YFP+) in bone marrow and spleen stimulated with vaccinia virus or CpG oligos. CpG oligos induce TLR9-dependent type I IFN production by pDCs, and the YFP+ cells in these cultures were B220+CD11c+, a surface phenotype consistent with that of pDCs (Fig. 5a). In contrast, the cells responding to vaccinia virus were B220- and had lower surface levels of CD11c (Fig. 5a). These distinct surface phenotypes clearly demonstrate that different cell types are responding to vaccinia virus and CpG oligos.

Bottom Line: The relevance of this recognition for antiviral immunity remains largely unexplained.TLR2-dependent induction of type I interferon occurred only in response to viral ligands, which indicates that TLR2 is able to discriminate between pathogen classes.Thus, the innate immune system can detect certain non-nucleic acid features of viruses and links this recognition to the induction of specific antiviral genes.

View Article: PubMed Central - PubMed

Affiliation: Division of Immunology and Pathogenesis, Department of Molecular & Cell Biology, University of California, Berkeley, California, USA.

ABSTRACT
Despite the paradigm that the innate immune system uses nucleic acid-specific receptors to detect viruses because of a lack of other conserved features, many viruses are recognized by Toll-like receptor 2 (TLR2) and TLR4. The relevance of this recognition for antiviral immunity remains largely unexplained. Here we report that TLR2 activation by viruses led to the production of type I interferon. TLR2-dependent induction of type I interferon occurred only in response to viral ligands, which indicates that TLR2 is able to discriminate between pathogen classes. We demonstrate that this specialized response was mediated by Ly6C(hi) inflammatory monocytes. Thus, the innate immune system can detect certain non-nucleic acid features of viruses and links this recognition to the induction of specific antiviral genes.

Show MeSH
Related in: MedlinePlus