The role of myeloid receptors on murine plasmacytoid dendritic cells in induction of type I interferon

The kinetics of inhibitory immune checkpoints during and post-COVID-19: the knowns and unknowns

The immune system is tightly regulated to prevent immune reactions to self-antigens and to avoid excessive immune responses during and after challenges from non-self-antigens. Inhibitory immune checkpoints (IICPs), as the major regulators of immune system responses, are extremely important for maintaining the homeostasis of cells and tissues. However, the high and sustained co-expression of IICPs in chronic infections, under persistent antigenic stimulations, results in reduced immune cell functioning and more severe and prolonged disease complications. Furthermore, IICPs-mediated interactions can be hijacked by pathogens in order to evade immune induction or effector mechanisms. Therefore, IICPs can be potential targets for the prognosis and treatment of chronic infectious diseases. This is especially the case with regards to the most challenging infectious disease of recent times, coronavirus disease-2019 (COVID-19), whose long-term complications can persist long after recovery. This article reviews the current knowledge about the kinetics and functioning of the IICPs during and post-COVID-19.

Tandem bispecific antibody prevents pathogenic SHIVSF162P3CN infection and disease progression

Although progress has been made on constructing potent bi-specific broadly neutralizing antibody (bi-bNAb), few bi-bNAbs have been evaluated against HIV-1/AIDS in non-human primates (NHPs). Here, we report the efficacy of a tandem bi-bNAb, namely BiIA-SG, in Chinese-origin rhesus macaques (CRM) against the CRM-adapted R5-tropic pathogenic SHIV_SF162P3CN challenge. Pre-exposure BiIA-SG injection prevents productive viral infection in 6 of 6 CRMs with unmeasurable proviral load, T cell responses, and seroconversion. Single BiIA-SG injection, at day 1 or 3 post viral challenge, significantly reduces peak viremia, achieves undetectable setpoint viremia in 8 of 13 CRMs, and delays disease progression for years in treated CRMs. In contrast, 6 of 8 untreated CRMs develop simian AIDS within 2 years. BiIA-SG-induced long-term protection is associated with CD8⁺ T cells as determined by anti-CD8β antibody depletion experiments. Our findings provide a proof-of-concept that bi-bNAb treatment elicits T cell immunity in NHPs, which warrant the clinical development of BiIA-SG for HIV-1 prevention and immunotherapy.

Nitric Oxide Regulates Macrophage Fungicidal Activity via S-nitrosylation of Dectin-1

Introduction: Recognition of fungal surface β-glucan by pattern recognition receptor Dectin-1 is a critical process for fungal clearance in the lung. In humans, persistent fungal infection is observed in individuals with particular Dectin-1 polymorphism. We have identified that nitric oxide (NO) modifies critical cysteines in pattern recognition molecules to disassemble and alter protein function. There is a hydrophobic S-nitrosylation motif present in surfactant protein-D (SP-D) that is also present in Dectin-1. We hypothesized that Dectin-1 can be modified by nitrosative stress potentially leading to impairment of fungal clearance. Materials and Methods: Recombinant Dectin-1 was incubated with l-nitrosocysteine (L-SNOC) and S-nitrosylated Dectin-1 was detected by Biotin-switch assay. Cells of a murine macrophage line (Raw 264.7) were incubated with S-nitroso-glutathione (GSNO) and Dectin-1 shedding from the cell surface was determined by Western blot. Dectin-1 quaternary structure was determined by native gel electrophoresis. Dectin-1 function was assayed by NF-κB activity and IL-6 mRNA real-time polymerase chain reaction (PCR). Phagocytic activity was measured by fluorescence labeled zymosan beads. Results: Dectin-1 was S-nitrosylated by l-nitrosocysteine (L-SNOC) in vitro, as determined by Biotin-switch assay, resulting in structural disruption. We used Western blotting and flow cytometry to demonstrate that incubation of a murine macrophage cell line (Raw 264.7 cells) with GSNO reduced the surface Dectin-1 expression as a result of shedding to the media. The shedding of Dectin-1 is due to formation of S-nitrosothiol (SNO)-Dectin-1 and disruption of the Dectin-1 oligomeric complex. GSNO also induces Dectin-1 shedding from the cell surface. The functional significance of GSNO treatment of macrophages is shown by reduced β-glucan-mediated signaling in terms of NF-κB function and IL-6 expression. Finally, it was demonstrated that GSNO treatment reduces the capability of macrophages to phagocytose zymosan. Conclusions: These data provide mechanistic data to support the role of Dectin-1 nitrosylation as a mediator of reduced fungal clearance in the face of increased NO exposure.

Recommendations for coronavirus infection in rheumatic diseases treated with biologic therapy

The Coronavirus-associated disease, that was first identified in 2019 in China (CoViD-19), is a pandemic caused by a bat-derived beta-coronavirus, named SARS-CoV2. It shares homology with SARS and MERS-CoV, responsible for past outbreaks in China and in Middle East. SARS-CoV2 spread from China where the first infections were described in December 2019 and is responsible for the respiratory symptoms that can lead to acute respiratory distress syndrome. A cytokine storm has been shown in patients who develop fatal complications, as observed in past coronavirus infections. The management includes ventilatory support and broad-spectrum antiviral drugs, empirically utilized, as a targeted therapy and vaccines have not been developed. Based upon our limited knowledge on the pathogenesis of CoViD-19, a potential role of some anti-rheumatic drugs may be hypothesized, acting as direct antivirals or targeting host immune response. Antimalarial drugs, commonly used in rheumatology, may alter the lysosomal proteases that mediates the viral entry into the cell and have demonstrated efficacy in improving the infection. Anti-IL-1 and anti-IL-6 may interfere with the cytokine storm in severe cases and use of tocilizumab has shown good outcomes in a small cohort. Baricitinib has both antiviral and anti-inflammatory properties. Checkpoints inhibitors such as anti-CD200 and anti-PD1 could have a role in the treatment of CoViD-19. Rheumatic disease patients taking immunosuppressive drugs should be recommended to maintain the chronic therapy, prevent infection by avoiding social contacts and pausing immunosuppressants in case of infection. National and international registries are being created to collect data on rheumatic patients with CoViD-19.

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CoViD-19 is a pandemic caused by SARS-CoV2, that can lead to acute respiratory distress syndrome.

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Antimalarial drugs, anti-IL-1 and anti-IL-6 may be used in severe cases targeting the cytokine storm induced by CoViD-19.

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Recommendations for rheumatic disease patients include the prevention of infection by avoiding social contacts.

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Patients should also continue their ongoing therapy except in the case of overt infection.

ER intrabody-mediated inhibition of interferon α secretion by mouse macrophages and dendritic cells

Interferon α (IFNα) counteracts viral infections by activating various IFNα-stimulated genes (ISGs). These genes encode proteins that block viral transport into the host cell and inhibit viral replication, gene transcription and translation. Due to the existence of 14 different, highly homologous isoforms of mouse IFNα, an IFNα knockout mouse has not yet been established by genetic knockout strategies. An scFv intrabody for holding back IFNα isoforms in the endoplasmic reticulum (ER) and thus counteracting IFNα secretion is reported. The intrabody was constructed from the variable domains of the anti-mouse IFNα rat monoclonal antibody 4EA1 recognizing the 5 isoforms IFNα1, IFNα2, IFNα4, IFNα5, IFNα6.

A soluble form of the intrabody had a K_D of 39 nM to IFNα4. It could be demonstrated that the anti-IFNα intrabody inhibits clearly recombinant IFNα4 secretion by HEK293T cells. In addition, the secretion of IFNα4 was effectively inhibited in stably transfected intrabody expressing RAW 264.7 macrophages and dendritic D1 cells. Colocalization of the intrabody with IFNα4 and the ER marker calnexin in HEK293T cells indicated complex formation of intrabody and IFNα4 inside the ER. Intracellular binding of intrabody and antigen was confirmed by co-immunoprecipitation. Complexes of endogenous IFNα and intrabody could be visualized in the ER of Poly (I:C) stimulated RAW 264.7 macrophages and D1 dendritic cells. Infection of macrophages and dendritic cells with the vesicular stomatitis virus VSV-AV2 is attenuated by IFNα and IFNβ. The intrabody increased virus proliferation in RAW 264.7 macrophages and D1 dendritic cells under IFNβ-neutralizing conditions. To analyze if all IFNα isoforms are recognized by the intrabody was not in the focus of this study. Provided that binding of the intrabody to all isoforms was confirmed, the establishment of transgenic intrabody mice would be promising for studying the function of IFNα during viral infection and autoimmune diseases.

Antifungal Activity of Plasmacytoid Dendritic Cells and the Impact of Chronic HIV Infection

Due to the effectiveness of combined antiretroviral therapy, people living with HIV can control viral replication and live longer lifespans than ever. However, HIV-positive individuals still face challenges to their health and well-being, including dysregulation of the immune system resulting from years of chronic immune activation, as well as opportunistic infections from pathogenic fungi. This review focuses on one of the key players in HIV immunology, the plasmacytoid dendritic cell (pDC), which links the innate and adaptive immune response and is notable for being the body’s most potent producer of type-I interferons (IFNs). During chronic HIV infection, the pDC compartment is greatly dysregulated, experiencing a substantial depletion in number and compromise in function. This immune dysregulation may leave patients further susceptible to opportunistic infections. This is especially important when considering a new role for pDCs currently emerging in the literature: in addition to their role in antiviral immunity, recent studies suggest that pDCs also play an important role in antifungal immunity. Supporting this new role, pDCs express C-type lectin receptors including dectin-1, dectin-2, dectin-3, and mannose receptor, and toll-like receptors-4 and -9 that are involved in recognition, signaling, and response to a wide variety of fungal pathogens, including Aspergillus fumigatus, Cryptococcus neoformans, Candida albicans, and Pneumocystis jirovecii. Accordingly, pDCs have been demonstrated to recognize and respond to certain pathogenic fungi, measured via activation, cytokine production, and fungistatic activity in vitro, while in vivo mouse models indicated a strikingly vital role for pDCs in survival against pulmonary Aspergillus challenge. Here, we discuss the role of the pDC compartment and the dysregulation it undergoes during chronic HIV infection, as well as what is known so far about the role and mechanisms of pDC antifungal activity.

Plasmacytoid dendritic cells and type 1 interferon promote peripheral expansion of forkhead box protein 3(+) regulatory T cells specific for the ubiquitous RNA-binding nuclear antigen La/Sjögren's syndrome (SS)-B

RNA-binding nuclear antigens are a major class of self-antigen to which immune tolerance is lost in rheumatic diseases. Serological tolerance to one such antigen, La/Sjögren's syndrome (SS)-B (La), is controlled by CD4(+) T cells. This study investigated peripheral tolerance to human La (hLa) by tracking the fate of hLa-specific CD4(+) T cells expressing the transgenic (Tg) 3B5.8 T cell receptor (TCR) after adoptive transfer into lymphocyte-replete recipient mice expressing hLa as a neo-self-antigen. After initial antigen-specific cell division, hLa-specific donor CD4(+) T cells expressed forkhead box protein 3 (FoxP3). Donor cells retrieved from hLa Tg recipients displayed impaired proliferation and secreted interleukin (IL)-10 in vitro in response to antigenic stimulation. Transfer of highly purified FoxP3-negative donor cells demonstrated that accumulation of hLa-specific regulatory T cells (Treg ) was due primarily to expansion of small numbers of donor Treg . Depletion of recipient plasmacytoid dendritic cells (pDC), but not B cells, severely hampered the accumulation of FoxP3(+) donor Treg in hLa Tg recipients. Recipient pDC expressed tolerogenic markers and higher levels of co-stimulatory and co-inhibitory molecules than B cells. Adoptive transfer of hLa peptide-loaded pDC into mice lacking expression of hLa recapitulated the accumulation of hLa-specific Treg . Blockade of the type 1 interferon (IFN) receptor in hLa Tg recipients of hLa-specific T cells impaired FoxP3(+) donor T cell accumulation. Therefore, peripheral expansion of Treg specific for an RNA-binding nuclear antigen is mediated by antigen-presenting pDC in a type 1 IFN-dependent manner. These results reveal a regulatory function of pDC in controlling autoreactivity to RNA-binding nuclear antigens.

Antifungal Activity of Plasmacytoid Dendritic Cells against Cryptococcus neoformans In Vitro Requires Expression of Dectin-3 (CLEC4D) and Reactive Oxygen Species

Conventional dendritic cells (cDCs) are critical for protection against pulmonary infection with the opportunistic fungal pathogen Cryptococcus neoformans; however, the role of plasmacytoid dendritic cells (pDCs) is unknown. We show for the first time that murine pDCs have direct activity against C. neoformans via reactive oxygen species (ROS), a mechanism different from that employed to control Aspergillus fumigatus infections. The anticryptococcal activity of murine pDCs is independent of opsonization but appears to require the C-type lectin receptor Dectin-3, a receptor not previously evaluated during cryptococcal infections. Human pDCs can also inhibit cryptococcal growth by a mechanism similar to that of murine pDCs. Experimental pulmonary infection of mice with a C. neoformans strain that induces protective immunity demonstrated that recruitment of pDCs to the lungs is CXCR3 dependent. Taken together, our results show that pDCs inhibit C. neoformans growth in vitro via the production of ROS and that Dectin-3 is required for optimal growth-inhibitory activity.

Recognition of Aspergillus fumigatus hyphae by human plasmacytoid dendritic cells is mediated by dectin-2 and results in formation of extracellular traps

Plasmacytoid dendritic cells (pDCs) were initially considered as critical for innate immunity to viruses. However, our group has shown that pDCs bind to and inhibit the growth of Aspergillus fumigatus hyphae and that depletion of pDCs renders mice hypersusceptible to experimental aspergillosis. In this study, we examined pDC receptors contributing to hyphal recognition and downstream events in pDCs stimulated by A. fumigatus hyphae. Our data show that Dectin-2, but not Dectin-1, participates in A. fumigatus hyphal recognition, TNF-α and IFN-α release, and antifungal activity. Moreover, Dectin-2 acts in cooperation with the FcRγ chain to trigger signaling responses. In addition, using confocal and electron microscopy we demonstrated that the interaction between pDCs and A. fumigatus induced the formation of pDC extracellular traps (pETs) containing DNA and citrullinated histone H3. These structures closely resembled those of neutrophil extracellular traps (NETs). The microarray analysis of the pDC transcriptome upon A. fumigatus infection also demonstrated up-regulated expression of genes associated with apoptosis as well as type I interferon-induced genes. Thus, human pDCs directly recognize A. fumigatus hyphae via Dectin-2; this interaction results in cytokine release and antifungal activity. Moreover, hyphal stimulation of pDCs triggers a distinct pattern of pDC gene expression and leads to pET formation.

The rhesus rhadinovirus CD200 homologue affects immune responses and viral loads during in vivo infection

Rhesus macaque rhadinovirus (RRV) is a gammaherpesvirus of rhesus macaque (RM) monkeys that is closely related to human herpesvirus 8 (HHV-8)/Kaposi's Sarcoma-associated herpesvirus (KSHV), and it is capable of inducing diseases in simian immunodeficiency virus (SIV)-infected RM that are similar to those seen in humans coinfected with HIV and HHV-8. Both HHV-8 and RRV encode viral CD200 (vCD200) molecules that are homologues of cellular CD200, a membrane glycoprotein that regulates immune responses and helps maintain immune homeostasis via interactions with the CD200 receptor (CD200R). Though the functions of RRV and HHV-8 vCD200 molecules have been examined in vitro, the precise roles that these viral proteins play during in vivo infection remain unknown. Thus, to address the contributions of RRV vCD200 to immune regulation and disease in vivo, we generated a form of RRV that lacked expression of vCD200 for use in infection studies in RM. Our data indicated that RRV vCD200 expression limits immune responses against RRV at early times postinfection and also impacts viral loads, but it does not appear to have significant effects on disease development. Further, examination of the distribution pattern of CD200R in RM indicated that this receptor is expressed on a majority of cells in peripheral blood mononuclear cells, including B and T cells, suggesting potentially wider regulatory capabilities for both vCD200 and CD200 that are not strictly limited to myeloid lineage cells. In addition, we also demonstrate that RRV infection affects CD200R expression levels in vivo, although vCD200 expression does not play a role in this phenomenon.

IMPORTANCE

Cellular CD200 and its receptor, CD200R, compose a pathway that is important in regulating immune responses and is known to play a role in a variety of human diseases. A number of pathogens have been found to modulate the CD200-CD200R pathway during infection, including human herpesvirus 8 (HHV-8), the causative agent of Kaposi's sarcoma and B cell neoplasms in AIDS patients, and a closely related primate virus, rhesus macaque rhadinovirus (RRV), which infects and induces disease in rhesus macaque monkeys. HHV-8 and RRV encode homologues of CD200, termed vCD200, which are thought to play a role in preventing immune responses against these viruses. However, neither molecule has been studied in an in vivo model of infection to address their actual contributions to immunoregulation and disease. Here we report findings from our studies in which we analyzed the properties of a mutant form of RRV that lacks vCD200 expression in infected rhesus macaques.

Whole blood stimulation with Toll-like receptor (TLR)-7/8 and TLR-9 agonists induces interleukin-12p40 expression in plasmacytoid dendritic cells in rhesus macaques but not in humans

Macaques provide important animal models in biomedical research into infectious and chronic inflammatory disease. Therefore, a proper understanding of the similarities and differences in immune function between macaques and humans is needed for adequate interpretation of the data and translation to the human situation. Dendritic cells are important as key regulators of innate and adaptive immune responses. Using a new whole blood assay we investigated functional characteristics of blood plasmacytoid dendritic cells (pDC), myeloid dendritic cells (mDC) and monocytes in rhesus macaques by studying induction of activation markers and cytokine expression upon Toll-like receptor (TLR) stimulation. In a head-to-head comparison we observed that rhesus macaque venous blood contained relatively lower numbers of pDC than human venous blood, while mDC and monocytes were present at similar percentages. In contrast to humans, pDC in rhesus macaques expressed the interleukin (IL)-12p40 subunit in response to TLR-7/8 as well as TLR-9 stimulation. Expression of IL-12p40 was confirmed by using different monoclonal antibodies and by reverse transcription-polymerase chain reaction (RT-PCR). Both in humans and rhesus macaques, TLR-4 stimulation induced IL-12p40 expression in mDC and monocytes, but not in pDC. The data show that, in contrast to humans, pDC in macaques are able to express IL-12p40, which could have consequences for evaluation of human vaccine candidates and viral infection.

Expression of selected regulatory molecules on the CD83+ monocyte-derived dendritic cells generated from patients with laryngeal cancer and their clinical significance

B7H1 and B7H4 overexpression is associated with inhibition of the immune system in many solid tumors, and altogether with CD200 molecule plays an important role in tumor invasion by promoting malignant transformation. However, there is no report about impact of these molecules on laryngeal squamous cell carcinoma. The objective of the present study was to assess by means of flow cytometry the expression of B7H1, B7H4, CD200, and CD200R on CD83+ monocyte-derived dendritic cells (Mo-DC), pulsed with autologous tumor cell lysates (aTCL) in patients who suffer from G1, G2, or G3 laryngeal carcinoma (LC, n = 60) in comparison to healthy donors (HD, n = 15). It has been demonstrated that median value of the percentages of CD83+ B7H1+, CD83+ B7H4+, and CD83+ CD200+ cells were higher in LC patients than HD (p = 0.041, p ≤ 0.0001, and p = 0.02, respectively). Mean fluorescence intensity (MFI) of CD200, CD200R, B7H1, and B7H4 on the Mo-DC pulsed with aTCL of the patients was also higher than on the Mo-DC of HD (p ≤ 0.0001, p ≤ 0.0001, p = 0.002, and p ≤ 0.0001, respectively). The highest MFI levels of all molecules were noted in grade 3 LC. The aforementioned results prove that there is a relation between the presence of laryngeal cancer and the expression of B7H1, B7H4, CD200, and CD200R regulatory molecules on the CD83+ Mo-DC pulsed with autologous cancer cell lysates. Strong association of LC grade and the tested antigens expression suggests a critical role for these proteins in LC biology.

Cell receptors for influenza a viruses and the innate immune response

The interaction of the hemagglutinin (HA) of the influenza A viruses (IAV) with the cell surface is a key factor for entry of the virus and productive infection of the cell. This glycoprotein has affinity for sialic acids (SA), and different strains present specificity for SA bound through α2,3 or α2,6 linkages to the underlying sugar chain, which is usually related with host and cell tropism. Nucleic acid recognizing receptors (mainly RIG-I and Toll-like receptors) are the most extensively studied pattern recognition receptors for IAV. However, due to the ability of the HA of avian, swine, or human influenza viruses to bind differently linked SA and also to the high levels and variability of glycosylations of their major virion glycoprotein components, HA and NA, IAV interacting proteins on the cell surface could also play an important role in initiating different signaling pathways to elicit the immune response in infected cells. But, at present, these processes are not well understood. In this mini-review we discuss how the interactions of IAV with cell surface receptors on immune cells might be important for the induction of specific innate immune responses and as a result, for pathogenicity in humans.