The differing pathophysiologies that underlie COVID-19-associated perniosis and thrombotic retiform purpura: a case series.

BACKGROUND: There are two distinctive acral manifestations of COVID-19 embodying disparate clinical phenotypes. One is perniosis occurring in mildly symptomatic patients, typically children and young adults; the second is the thrombotic retiform purpura of critically ill adults with COVID-19. OBJECTIVES: To compare the clinical and pathological profiles of these two different cutaneous manifestations of COVID-19. METHODS: We compared the light microscopic, phenotypic, cytokine and SARS-CoV-2 protein and RNA profiles of COVID-19-associated perniosis with that of thrombotic retiform purpura in critical patients with COVID-19. RESULTS: Biopsies of COVID-19-associated perniosis exhibited vasocentric and eccrinotropic T-cell- and monocyte-derived CD11c+ , CD14+ and CD123+ dendritic cell infiltrates. Both COVID-associated and idiopathic perniosis showed striking expression of the type I interferon-inducible myxovirus resistance protein A (MXA), an established marker for type I interferon signalling in tissue. SARS-CoV-2 RNA, interleukin-6 and caspase 3 were minimally expressed and confined to mononuclear inflammatory cells. The biopsies from livedo/retiform purpura showed pauci-inflammatory vascular thrombosis without any MXA decoration. Blood vessels exhibited extensive complement deposition with endothelial cell localization of SARS-CoV-2 protein, interleukin-6 and caspase 3; SARS-CoV-2 RNA was not seen. CONCLUSIONS: COVID-19-associated perniosis represents a virally triggered exaggerated immune reaction with significant type I interferon signaling. This is important to SARS-CoV-2 eradication and has implications in regards to a more generalized highly inflammatory response. We hypothesize that in the thrombotic retiform purpura of critically ill patients with COVID-19, the vascular thrombosis in the skin and other organ systems is associated with a minimal interferon response. This allows excessive viral replication with release of viral proteins that localize to extrapulmonary endothelium and trigger extensive complement activation.

Diagnostic potential of sarcoplasmic myxovirus resistance protein A expression in subsets of dermatomyositis.

AIMS: To elucidate the diagnostic value of sarcoplasmic expression of myxovirus resistance protein A (MxA) for dermatomyositis (DM) specifically analysing different DM subforms, and to test the superiority of MxA to other markers. METHODS: Immunohistochemistry for MxA and retinoic acid-inducible gene I (RIG-I) was performed on skeletal muscle samples and compared with the item presence of perifascicular atrophy (PFA) in 57 DM patients with anti-Mi-2 (n = 6), -transcription intermediary factor 1 gamma (n = 10), -nuclear matrix protein 2 (n = 13), -melanoma differentiation-associated gene 5 (MDA5) (n = 10) or -small ubiquitin-like modifier activating enzyme (n = 1) autoantibodies and with no detectable autoantibody (n = 17). Among the patients, nine suffered from cancer and 22 were juvenile-onset type. Disease controls included antisynthetase syndrome (ASS)-associated myositis (n = 30), immune-mediated necrotizing myopathy (n = 9) and inclusion body myositis (n = 5). RESULTS: Sarcoplasmic MxA expression featured 77% sensitivity and 100% specificity for overall DM patients, while RIG-I staining and PFA reached respectively 14% and 59% sensitivity and 100% and 86% specificity. In any subset of DM, sarcoplasmic MxA expression showed higher sensitivity than RIG-I and PFA. Some anti-MDA5 antibody-positive DM samples distinctively showed a scattered staining pattern of MxA. No ASS samples had sarcoplasmic MxA expression even though six patients had DM skin rash. CONCLUSIONS: Sarcoplasmic MxA expression is more sensitive than PFA and RIG-I expression for a pathological diagnosis of DM, regardless of the autoantibody-related subgroup. In light of its high sensitivity and specificity, it may be considered a pathological hallmark of DM per se. Also, lack of MxA expression in ASS supports the idea that ASS is a distinct entity from DM.

Inflammasome Activation Characterizes Lesional Skin of Folliculitis Decalvans.

Folliculitis decalvans (FD) is a chronic inflammatory disease leading to scarring alopecia with poorly defined pathogenesis. The aim of this study was to investigate the expression of markers associated with the activation of innate immune signals, such as inflammasome (NALP1 and NALP3), interleukin (IL)-1ß and IL-8 and type I interferon (MxA). A retrospective monocentric study was conducted and included 17 patients with FD with available biopsies. Disease activity (stable vs. active) was defined clinically and histologically. Immunostaining was performed using antibodies directed against NALP1, NALP3, IL-1ß, IL-8, and MxA on FD skin biopsies. Results were compared with normal controls and lichen planopilaris. Eleven patients had active disease and 6 had stable disease. NALP1, NALP3, and IL-1ß expression were significantly increased in hair follicles in FD compared with controls and lichen planopilaris. This study highlights the predominant immune signal associated with inflammasome activation in FD, suggesting the use of IL-1ß blockade in FD.

Evaluation of the Diagnostic Value of Plasmacytoid Dendritic Cells in Differentiating the Lymphocytic Cicatricial Alopecias.

BACKGROUND: Differentiating lymphocytic scarring alopecias may be difficult clinically as well as histopathologically. OBJECTIVE: To investigate plasmacytoid dendritic cell (PDC) presence and distribution patterns and their diagnostic value in differentiating scarring alopecias of lupus erythematosus (LE) from lichen planopilaris (LPP) and frontal fibrosing alopecia (FFA). METHODS: Seventeen LE-associated alopecia, 20 LPP and 10 FFA cases were immunohistochemically tested for PDC presence/distribution and activity. RESULTS: LE-associated alopecia showed increased PDC content (≥10% PDCs in all cases and ≥50% in 94% of cases), PDC clusters (100% of cases), and deeper dermal and perieccrine distribution (100% of cases) with involvement of the dermoepidermal junction (DEJ, 94% of cases), while the majority of LPP and FFA had <10% PDC content that was mainly confined to the upper dermis surrounding the hair infundibulum with rare DEJ involvement and rare clustering. CONCLUSIONS: Specific PDC-related parameters may serve as a useful diagnostic adjunct in the differentiation between LE-associated alopecia versus LPP and FFA.

Glomerular expression of myxovirus resistance protein 1 in human mesangial cells: possible activation of innate immunity in the pathogenesis of lupus nephritis.

Since viral infections activate type I interferon (IFN) pathways and cause subsequent release of IFN-dependent proinflammatory chemokines and cytokines, the innate immune system plays an important role in the pathogenesis of lupus nephritis (LN). It has been reported that human myxovirus resistance protein 1 (Mx1), a type I IFN-dependent transcript, acts against a wide range of RNA viruses. Although the expression of Mx1 in biopsy specimens obtained from patients with dermatomyositis and cutaneous lupus has been described, the expression of Mx1 in human mesangial cells (MCs) has remained largely unknown. We treated normal human MCs in culture with polyinosinic-polycytidylic acid (poly IC), an authentic double-stranded RNA, and analyzed the expression of Mx1 by reverse transcription-polymerase chain reaction and western blotting. To elucidate the poly IC-signalling pathway, we subjected the cells to RNA interference against IFN-ß. We also conducted an immunofluorescence study to examine mesangial Mx1 expression in biopsy specimens from patients with LN. Poly IC-induced Mx1 expression in MCs are shown both time- and dose-dependently, and RNA interference against IFN-ß inhibited poly IC-induced Mx1 expression. Intense glomerular Mx1 expression was observed in biopsy specimens from patients with LN, whereas negative staining occurred in specimens from patients with IgA nephropathy or purpura nephritis. These preliminary observations support, at least in part, the theory of innate immune system activation in the pathogenesis of LN.

Interferon induced Mx protein from Indian snow trout Schizothorax richardsonii (Gray) lacks critical functional features unlike its mammalian homologues.

Viral attack within host cells triggers the production of type I interferons and leads to the induction of interferon stimulated genes (ISGs). One of the ISG Mx, encodes type I interferon inducible GTPase that is responsible for the establishment of an anti-viral state within cells. Intriguingly, several isoforms of Mx have been reported in fish, but the structural analysis of fish Mx proteins remains unexplored. For the first time, we have identified and unraveled the molecular structure of Mx protein from Indian snow trout, Schizothorax richardsonii (Gray) a Coldwater fish that inhabits the water bodies in the sub-Himalayan region. The snow trout Mx coding region consists of 2518 nucleotides with an open reading frame (ORF) of 1854 nucleotides. It codes for a polypeptide of 617 amino acids with a predicted molecular weight of 70 kDa. In silico analysis of snow trout Mx protein revealed signature of dynamin family (LPRGTGIVTR) along with a tripartite GTP-binding domain (GDQSSGKS, DLPG, and TKPD). Homology modelling established that the Mx protein is an elongated structure with a G domain, bundle signaling element (BSE) and a GTPase effector domain (GED). Moreover, the GED of Mx contains two highly conserved leucine zippers at the COOH-terminal of the protein suggesting its structural similarity with human homologues. However, snow trout Mx lacks the essential features of its mammalian homologues questioning its functional characteristics. Further, a ligand binding site in the said protein has also been predicted adjacent to the GTPase switch within the G domain.

Respiratory Syncytial Virus Persistence in Murine Macrophages Impairs IFN-ß Response but Not Synthesis.

Type-I interferon (IFN-I) production is an early response to viral infection and pathogenic viruses have evolved multiple strategies to evade this cellular defense. Some viruses can establish and maintain persistent infections by altering the IFN-I signaling pathway. Here, we studied IFN-I synthesis and response in an in vitro model of persistent infection by respiratory syncytial virus (RSV) in a murine macrophage-like cell line. In this model, interferon regulatory factor 3 was constitutively active and located at nuclei of persistently infected cells, inducing expression of IFN-beta mRNA and protein. However, persistently infected macrophages did not respond in an autocrine manner to the secreted-IFN-beta or to recombinant-IFN-beta, since phosphorylated-STAT1 was not detected by western blot and transcription of the interferon-stimulated genes (ISGs) Mx1 and ISG56 was not induced. Treatment of non-infected macrophages with supernatants from persistently infected cells induced STAT1 phosphorylation and ISGs expression, mediated by the IFN-I present in the supernatants, because blocking the IFN-I receptor inhibited STAT1 phosphorylation. Results suggest that the lack of autocrine response to IFN-I by the host cell may be one mechanism for maintenance of RSV persistence. Furthermore, STAT1 phosphorylation and ISGs expression induced in non-infected cells by supernatants from persistently infected macrophages suggest that RSV persistence may trigger a proinflammatory phenotype in non-infected cells as part of the pathogenesis of RSV infection.

Biological monitoring of IFN-ß therapy in Multiple Sclerosis.

Multiple Sclerosis (MS) is a heterogeneous disease and a variable percentage of patients are non-responders to common treatment. Early diagnosis of non-responders allows change to a more useful therapy for the patient and better allocates a large amount of financial resources. Quantification of Neutralizing antibodies (Nabs) and of biological activity of IFN-ß are recognized approaches to identify immuno-pharmacological non-responders. A consistent number of studies have demonstrated that quantification of Myxovirus-induced protein A (MxA) is a valid biomarker to detect immune-pharmacological non responders after one year of treatment. Persistent high titre of Nabs and absence of biological activity predict abolition of IFN-ß effects in disease activity measured through MRI, number of relapses and disability. Guidelines and flow-charts including both Nabs and MxA quantification are presented.

Histiocytoid Sweet's Syndrome: A localized cutaneous proliferation of macrophages frequently associated with chronic myeloproliferative disease.

BACKGROUND: Histiocytoid Sweet's syndrome was originally described as cutaneous lesions of Sweet's syndrome where the infiltrate is mostly composed of histiocytoid mononuclear cells. The putative cell has been interpreted as an immature neutrophil based on the intense expression of myeloperoxidase. METHODS: To better understand the nature of the infiltrate and potential mechanisms leading to this distinct form of cutaneous inflammatory cell influx, thirteen cases of histiocytoid Sweet's syndrome, encountered in the routine and consult practice of one of the authors, were studied. The clinical features and microscopic findings are summarized. RESULTS: The study comprised eight men and five women aged from 23 to 80. There was a significant association with underlying myeloproliferative disease. In particular, five patients had underlying myelodysplastic syndrome. One patient had unspecified chronic myeloproliferative disorder and another had AML. Two cases were triggered by drug therapy (Cox-2 inhibitors). One patient had familial Mediterranean fever. The eruption was asymptomatic and an aggressive clinical course was not observed in most cases. Skin biopsies were composed of striking angiocentric and intersititial mononuclear cell infiltrates, often accentuated in the deeper dermis and subcutaneous fat. There was marked leukocytoclasia. Neutrophils were sparce or absent. These cells were strongly positive for CD163 and either expressed CD16 or myeloperoxidase. Variable positivity for myeloid dendritic cell markers including CD11c, BDCA-3, TCL1 oncogene, MXA and CD123 was observed. CONCLUSION: The histiocytoid cells of histiocytoid Sweet's syndrome define a novel subset of activated monocytes. This variant of Sweet's syndrome has a significant association with underlying myeloproliferative disease.