Apoptotic cells induce CD103 expression and immunoregulatory function in myeloid dendritic cell precursors through integrin αv and TGF-β activation

Ailiang Zhang,John Savill,Helena Paidassi,Adam Lacy-Hulbert,Jean Kanellopoulos

doi:10.1371/journal.pone.0232307

Ailiang Zhang, John Savill + Show 3 more

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https://doi.org/10.1371/journal.pone.0232307

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Abstract

In the mammalian gut CD103+ve myeloid DCs are known to suppress inflammation threatened by luminal bacteria, but stimuli driving DC precursor maturation towards this beneficial phenotype are incompletely understood. We isolated CD11+ve DCs from mesenteric lymph nodes (MLNs) of healthy mice; CD103+ve DCs were 8–24 fold more likely than CD103-ve DCs to exhibit extensive of prior phagocytosis of apoptotic intestinal epithelial cells. However, CD103+ve and CD103-ve MLN DCs exhibited similar ex vivo capacity to ingest apoptotic cells, indicating that apoptotic cells might drive immature DC maturation towards the CD103+ve phenotype. When cultured with apoptotic cells, myeloid DC precursors isolated from murine bone marrow and characterised as lineage-ve CD103-ve, displayed enhanced expression of CD103 and β8 integrin and acquired increased capacity to induce T regulatory lymphocytes (Tregs) after 7d in vitro. However, DC precursors isolated from αv-tie2 mice lacking αv integrins in the myeloid line exhibited reduced binding of apoptotic cells and complete deficiency in the capacity of apoptotic cells and/or latent TGF-β1 to enhance CD103 expression in culture, whereas active TGF-β1 increased DC precursor CD103 expression irrespective of αv expression. Fluorescence microscopy revealed clustering of αv integrin chains and latent TGF-β1 at points of contact between DC precursors and apoptotic cells. We conclude that myeloid DC precursors can deploy αv integrin to orchestrate binding of apoptotic cells, activation of latent TGF-β1 and acquisition of the immunoregulatory CD103+ve β8+ve DC phenotype. This implies that a hitherto unrecognised consequence of apoptotic cell interaction with myeloid phagocytes is programming that prevents inflammation.

Highlights

Mammalian bowel contents are laden with potently pro-inflammatory bacteria and yet the healthy gut is not inflamed
CD103 +ve myeloid Dendritic cells (DCs) have been characterised in detail in the mouse, with compelling evidence for key roles in keeping the healthy gut free of inflammation, by induction of T regulatory lymphocytes (Tregs) and other mechanisms dependent on TGF-β1 activation [2, 3, 5, 19, 25]
We demonstrate that CD103+ve DCs isolated from the mesenteric lymph nodes (MLNs) of healthy mice exhibited extensive evidence of prior ingestion of intestinal epithelial cells (IECs) undergoing spontaneous apoptosis whereas, depending on the straining technique used to identify previously ingested apoptotic IECs, CD103-ve MLN DCs were 8–24 fold less likely to do so

Summary

Introduction

Mammalian bowel contents are laden with potently pro-inflammatory bacteria and yet the healthy gut is not inflamed. We conclude that immature myeloid dendritic cell precursors can deploy αv integrins to capture apoptotic cells and co-ordinately activate latent TGF-β1 with the result that such precursors mature towards the CD103+ve immunoregulatory DC phenotype Such DCs are known to be crucial in suppression of inflammation in the murine gut [2,3,4,5,6] and the current study confirms that CD103+ve DCs migrating to mesenteric lymph nodes exhibit extensive evidence of prior ingestion of apoptotic cells arising spontaneously in the gut wall. These data suggest that future studies should examine whether tonic suppression of inflammation in the gastrointestinal tract is a newly identified function for clearance of apoptotic cells in addition to those previously described in resolution and repair of established inflammation [14,15,16]

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