Date Published: July 29, 2019
Publisher: Public Library of Science
Author(s): Erin Heather Doyle, Adeeb Rahman, Costica Aloman, Arielle L. Klepper, Ahmed El-Shamy, Francis Eng, Chiara Rocha, Sang Kim, Brandy Haydel, Sander S. Florman, M. Isabel Fiel, Thomas Schiano, Andrea D. Branch, Glenn Randall.
Plasmacytoid dendritic cells (pDCs) are “natural” interferon α (IFNα)-producing cells. Despite their importance to antiviral defense, autoimmunity, and ischemic liver graft injury, because DC subsets are rare and heterogeneous, basic questions about liver pDC function and capacity to make cytokines remain unanswered. Previous investigations failed to consistently detect IFNα mRNA in HCV-infected livers, suggesting that pDCs may be incapable of producing IFNα. We used a combination of molecular, biochemical, cytometric, and high-dimensional techniques to analyze DC frequencies/functions in liver and peripheral blood mononuclear cells (PBMCs) of hepatitis C virus (HCV)-infected patients, to examine correlations between DC function and gene expression of matched whole liver tissue and liver mononuclear cells (LMCs), and to determine if pDCs can produce multiple cytokines. T cells often produce multiple cytokines/chemokines but until recently technical limitations have precluded tests of polyfunctionality in individual pDCs. Mass cytometry (CyTOF) revealed that liver pDCs are the only LMC that produces detectable amounts of IFNα in response TLR-7/8 stimulation. Liver pDCs secreted large quantities of IFNα (~2 million molecules of IFNα/cell/hour) and produced more IFNα than PBMCs after stimulation, p = 0.0001. LMCs secreted >14-fold more IFNα than IFNλ in 4 hours. Liver pDC frequency positively correlated with whole liver expression of “IFNα-response” pathway (R2 = 0.58, p = 0.007) and “monocyte surface” signature (R2 = 0.54, p = 0.01). Mass cytometry revealed that IFNα-producing pDCs were highly polyfunctional; >90% also made 2–4 additional cytokines/chemokines of our test set of 10. Liver BDCA1 DCs, but not BDCA3 DCs, were similarly polyfunctional. pDCs from a healthy liver were also polyfunctional. Our data show that liver pDCs retain the ability to make abundant IFNα during chronic HCV infection and produce many other immune modulators. Polyfunctional liver pDCs are likely to be key drivers of inflammation and immune activation during chronic HCV infection.
Plasmacytoid dendritic cells (pDCs) are rare innate immune cells that comprise about 0.5% of peripheral blood mononuclear cells (PBMCs). They migrate into tissues and are known as “natural” producers of interferon alpha (IFNα). pDCs constitutively express toll-like receptor (TLR)-7 and TLR-9, as well as interferon regulatory factor (IRF)-7, enabling them to detect viral nucleic acids and to quickly secrete type I IFNs (IFNα and IFNβ), which bind neighboring cells and induce hundreds of IFN stimulated genes (ISGs), initiating antiviral defenses.
This is a detailed characterization of human liver pDCs from patients with a chronic hepatitis virus infection. It revealed that these rare innate immune cells are point sources of multiple immune activators and pro-inflammatory mediators, adding important new details about the fundamental capabilities of tissue-specific pDCs. Single cell mass cytometry (CyTOF) revealed that liver pDCs are the only IFNα producers among LMCs and revealed that only 15–40% synthesize it when stimulated with a TLR7/8 agonist (Figs 4D and 7D). Activated pDCs secreted large amounts of IFNα protein: ~2 million molecules per pDC per hour. While pDCs are traditionally known as “natural interferon producing cells,” our data revealed that they produce an array of bioactive molecules. Approximately 20% of pDCs make IFNα plus 4 of the other nine cytokines/chemokines we analyzed [TNFα, IL-8, IFNλ1 (IL-29), IL-6, IL-1β, IL-10, CCL3, CCL4, and CXCL10] and 13% make IFNα plus 5 or more (Fig 7A). Most IFNα+ pDCs expressed TNFα and IL-8, with variable amounts of IL-6, CCL3, CCL4, and IFNλ1 (IL-29). We did not determine the percentage of intrahepatic TNFα that is made by liver pDCs, but blood pDCs are major producers , suggesting that liver pDCs may be a significant source of this proinflammatory cytokine.