Human Plasmacytoid Dendritic Cells Express C-Type Lectin Receptors and Attach and Respond to Aspergillus fumigatus.

Plasmacytoid dendritic cells (pDCs) have been implicated as having a role in antifungal immunity, but mechanisms of their interaction with fungi and the resulting cellular responses are not well understood. In this study, we identify the direct and indirect biological response of human pDCs to the fungal pathogen Aspergillus fumigatus and characterize the expression and regulation of antifungal receptors on the pDC surface. Results indicate pDCs do not phagocytose Aspergillus conidia, but instead bind hyphal surfaces and undergo activation and maturation via the upregulation of costimulatory and maturation markers. Measuring the expression of C-type lectin receptors dectin-1, dectin-2, dectin-3, and mannose receptor on human pDCs revealed intermediate expression of each receptor compared with monocytes. The specific dectin-1 agonist curdlan induced pDC activation and maturation in a cell-intrinsic and cell-extrinsic manner. The indirect activation of pDCs by curdlan was much stronger than direct stimulation and was mediated through cytokine production by other PBMCs. Overall, our data indicate pDCs express various C-type lectin receptors, recognize and respond to Aspergillus hyphal Ag, and serve as immune enhancers or modulators in the overarching fungal immune response.

Frontline Science: AMPK regulates metabolic reprogramming necessary for interferon production in human plasmacytoid dendritic cells.

Plasmacytoid dendritic cells (pDCs) play a crucial role in innate viral immunity as the most potent producers of type I interferons (IFN) in the human body. However, the metabolic regulation of IFN production in such vast quantity remains poorly understood. In this study, AMP-activated protein kinase (AMPK) is strongly implicated as a driver of metabolic reprogramming that the authors and others have observed in pDCs after activation via TLR7/9. Oxygen consumption and mitochondrial membrane potential (MMP) were elevated following stimulation of pDCs with influenza or herpes simplex virus. Blocking these changes using mitochondrial inhibitors abrogated IFN-α production. While it appears that multiple carbon sources can be used by pDCs, blocking pyruvate metabolism had the strongest effect on IFN-α production. Furthermore, we saw no evidence of aerobic glycolysis (AG) during pDC activation and blocking lactate dehydrogenase activity did not inhibit IFN-α. TLR7/9 ligation induces a posttranslational modification in Raptor that is catalyzed by AMPK, and blocking TLR7/9 before virus introduction prevents this change. Finally, it is demonstrated that Dorsomorphin, an AMPK inhibitor, inhibited both IFN-α production and MMP in a dose-dependent manner. Taken together, these data reveal a potential cellular mechanism for the metabolic reprogramming in TLR 7/9-activated pDCs that supports activation and IFN-α production.

Regulation of Transcription Factor E2-2 in Human Plasmacytoid Dendritic Cells by Monocyte-Derived TNFα.

Plasmacytoid dendritic cells (pDCs) are innate immune cells and potent producers of interferon alpha (IFNα). Regulation of pDCs is crucial for prevention of aberrant IFN production. Transcription factor E2-2 (TCF4) regulates pDC development and function, but mechanisms of E2-2 control have not been investigated. We used freshly-isolated human peripheral blood mononuclear cells stimulated with toll-like receptor 7, 9, and 4 agonists to determine which factors regulate E2-2. After activation, pDCs decreased E2-2 expression. E2-2 downregulation occurred during the upregulation of costimulatory markers, after maximal IFN production. In congruence with previous reports in mice, we found that primary human pDCs that maintained high E2-2 levels produced more IFN, and had less expression of costimulatory markers. Stimulation of purified pDCs did not lead to E2-2 downregulation; therefore, we investigated if cytokine signaling regulates E2-2 expression. We found that tumor necrosis factor alpha (TNFα) produced by monocytes caused decreased E2-2 expression. All together, we established that primary human pDCs decrease E2-2 in response to TNFα and E2-2 low pDCs produce less IFN but exhibit more costimulatory molecules. Altered expression of E2-2 may represent a mechanism to attenuate IFN production and increase activation of the adaptive immune compartment.

Use, reuse or discard: quantitatively defined variance in N95 respirator integrity following vaporized hydrogen peroxide decontamination during the COVID-19 pandemic.

BACKGROUND: COVID-19 has stretched the ability of many institutions to supply needed personal protective equipment, especially N95 respirators. N95 decontamination and reuse programs provide one potential solution to this problem. Unfortunately, a comprehensive evaluation of the effects of decontamination on the integrity of various N95 models using a quantitative fit test (QTFT) approach is lacking. AIMS: 1) To investigate the effects of up to eight rounds of vaporized H2O2 (VHP) decontamination on the integrity of N95 respirators currently in use in a hospital setting. 2) To examine if N95 respirators worn by one user can adapt to the face shape of a second user with no compromise of integrity following VHP decontamination. METHODS: The PortaCount Pro+ Respirator Fit Tester Model 8038 was used to quantitatively define the integrity, measured by fit, of N95 respirators following decontamination with VHP. FINDINGS: There was an observable downward trend in the integrity of Halyard Fluidshield 46727 N95 respirators throughout eight cycles of decontamination with VHP. The integrity of 3M 1870 N95 respirators was significantly reduced after the respirator was worn, decontaminated with VHP, and then quantitatively fit tested on a second user. Furthermore, we uncovered inconsistencies between qualitative fit test and QTFT results that may have strong implications on the fit testing method used by institutions. CONCLUSIONS: Our data revealed variability in the integrity of different N95 models after VHP decontamination and exposed potential limitations of N95 decontamination and reuse programs.