Identification and Characterization of Novel Bone Marrow Myeloid DEC205+Gr-1+ Cell Subsets That Differentially Express Chemokine and TLRs

Abstract

Bone marrow-derived immunomodulatory cytokines impart a critical function in the regulation of innate immune responses and hemopoiesis. However, the source of immunomodulatory cytokines in murine bone marrow and the cellular immune mechanisms that control local cytokine secretion remain poorly defined. Herein, we identified a population of resident murine bone marrow myeloid DEC205+CD11c−B220−Gr1+CD8α−CD11b+ cells that respond to TLR2, TLR4, TLR7, TLR8, and TLR9 agonists as measured by the secretion of proinflammatory and anti-inflammatory cytokines in vitro. Phenotypic and functional analyses revealed that DEC205+CD11b+Gr-1+ bone marrow cells consist of heterogeneous populations of myeloid cells that can be divided into two main cell subsets based on chemokine and TLR gene expression profile. The DEC205+CD11b+Gr-1low cell subset expresses high levels of TLR7 and TLR9 and was the predominant source of IL-6, TNF-α, and IL-12 p70 production following stimulation with the TLR7 and TLR9 agonists CpG and R848, respectively. In contrast, the DEC205+CD11b+Gr-1high cell subset did not respond to CpG and R848 stimulation, which correlated with their lack of TLR7 and TLR9 expression. Similarly, a differential chemokine receptor expression profile was observed with higher expression of CCR1 and CXCR2 found in the DEC205+CD11+Gr-1high cell subset. Thus, we identified a previously uncharacterized population of resident bone marrow cells that may be implicated in the regulation of local immune responses in the bone marrow.

Bacterial signalling overrides cytokine signalling and modifies dendritic cell differentiation

“…The recent finding that haematopoietic stem cells express TLRs as well as associated accessory molecules and respond to stimulation by TLR agonists has redefined the extent to which innate pattern recognition controls immune responses 21,22 . In the present study, coculture of bone marrow progenitors with commensal bacteria inhibited DC differentiation and yielded cells with high Gr‐1 and low MHC‐II and CD11c expression; a phenotype indicative of both monocytes and myeloid suppressor cells.…”

“…Interestingly, bone marrow progenitor cells express pattern recognition receptors like Toll‐like receptors (TLRs) and can respond to pathogen‐associated molecular patterns that are common to both commensal and pathogenic bacteria. While the purpose of TLR expression on haematopoietic progenitor cells has not been conclusively identified, their presence and functionality indicate that innate signals could influence the differentiation of precursor cells 21,22 …”

“…While the purpose of TLR expression on haematopoietic progenitor cells has not been conclusively identified, their presence and functionality indicate that innate signals could influence the differentiation of precursor cells. 21,22 As precursor cells have recently been shown to enter peripheral tissues like the lamina propria of the small intestine, we sought to determine the possible outcome of interaction with commensal bacteria on these precursor cells using an in vitro coculture system. Here we show that bone marrow cells cocultured in granulocyte-macrophage colony-stimulating factor (GM-CSF) are arrested in the monocytic stage of differentiation following early bacterial exposure.…”

Enhanced Dendritic Cell-Induced Immune Responses Mediated by the Novel C-Type Lectin Receptor mDCAR1

“…All data are means Ϯ SEM of duplicate wells derived from supernatants of four independent experiments (significance was determined using the unpaired Student t test). (32). Furthermore, the administration of low doses of fluorochrome-conjugated anti-mDCAR1 mAb preferentially labeled CD8 ϩ DC rather than myeloid cells indicating that anti-mDCAR1 mAb predominantly targets CD8 ϩ DC after i.v.…”

“…As flow cytometric analysis revealed, F4/80 expression on mDCAR1 ϩ cells was low compared with classical macrophages, confirming that mDCAR1 ϩ cells are distinct from F4/80 ϩ red pulp macrophages in spleen. Based on the coexpression of CD205, the majority of mDCAR1 ϩ myeloid cells correspond to the DEC205 ϩ Gr-1 low population reported by Lamb et al (32), whereas a minority of mDCAR1 ϩ cells display a different phenotype. Furthermore, we have evidence, that mDCAR1 ϩ myeloid cells reflect certain precursor cells in BM (S. A. Kaden et al, manuscript in preparation).…”