COVID-19 and autoimmune bullous diseases: Lessons learned.

Both COVID-19 and autoimmune bullous diseases represent potentially life-threatening conditions. Autoimmunity has been a special focus during the COVID-19 pandemic considering the possible detrimental mutual influence between COVID-19 and autoimmune disorders as well as their supposed induction or triggering by SARS-CoV-2 vaccines. There is a growing need to assess the impact of the current pandemic particularly in patients with autoimmune bullous diseases requiring potent and long-term immunosuppressive treatments. This review provides the relevant state-of-the-art knowledge, including our own research, about immunobullous diseases in relation to COVID-19 and summarizes expert perspectives on their management throughout the pandemic.

Bullous pemphigoid anti-BP180-NC16A autoantibody reactivity in healthy individuals is associated with marked hypovitaminosis D and Th2-like cytokine predominance.

Autoimmune bullous disease autoantibodies, particularly including bullous pemphigoid (BP)-related anti-BP180-NC16A IgG, have been reported in a small subset of healthy individuals, but information about associated factors is lacking. We hypothesized that an abnormal status of immunomodulatory vitamin D could play a role in anti-BP180-NC16A autoantibody reactivity in healthy persons. In addition, we aimed to evaluate the cytokine profile associated with these autoantibodies. Plasma samples from 34 anti-BP180-NC16A IgG-reactive and 85 anti-BP180-NC16A IgG-negative healthy blood donors were tested for levels of 25-hydroxyvitamin D [25(OH)D] and a wide range of cytokines (IL-2, IL-4, IL-5, IL-6, IL-9, IL-10, IL-13, IL-17A, IL-17F, IL-21, IL-22, IFN-γ, and TNF-α). We observed that anti-BP180-NC16A IgG-reactive healthy subjects had significantly lower plasma 25(OH)D levels and about a two-fold higher rate of vitamin D deficiency (< 20 ng/ml) compared to anti-BP180-NC16A IgG-negative healthy persons. In addition, anti-BP180-NC16A IgG-positive samples were characterized by significantly higher levels of IL-2, IL-5, IL-9, IL-10, and IL-13 which were, however, not significantly associated with the vitamin D levels. Our results indicate that healthy individuals with BP autoantibody reactivity share similarities with BP patients regarding the vitamin D status and cytokine profile (i.e., marked hypovitaminosis D and Th2 predominance), which may have pathophysiologic implications.

Differences in the detection of circulating Hsp90 alpha between patients with atopic dermatitis and dermatitis herpetiformis.

Heat shock protein 90 alpha (Hsp90α) is one of the key intra- and extracellular chaperones responsible for the biological activity of various signaling molecules that are involved in (auto)immune-mediated inflammatory diseases. Recent epidemiologic data suggest that patients with atopic dermatitis (AD) are at risk for several autoimmune diseases, including dermatitis herpetiformis (DH), an extraintestinal manifestation of celiac disease (CD). In addition, pruritic diseases such as AD may be confused clinically with DH. In this study, we aimed to determine the role of circulating Hsp90α in patients with AD in relation to patients with DH, CD, and healthy controls. Using an enzyme-linked immunosorbent assay, levels of circulating Hsp90α were determined in serum samples derived from patients with AD (n = 31), DH (n = 26), CD (n = 15), and healthy controls (n = 55). Although serum concentrations of Hsp90α were similar between patients with DH, CD, and healthy controls, we found that serum levels of Hsp90α were significantly higher (mean value of 5.08-fold; p < 0.0001) in patients with AD when compared to patients with DH. A cutoff value calculated as 2 × standard deviation above the mean concentration of Hsp90α in DH patients revealed that 83.9% (26/31) of AD patients were Hsp90α positive, whereas none of the DH patients (0/26) displayed such a positivity. This preliminary study suggests a distinct role for extracellular Hsp90α in the pathogenesis of AD compared to DH and its potential use in distinguishing AD from DH. Nevertheless, the potential role of the evaluation of extracellular Hsp90α for distinguishing between AD and DH is at present speculative and requires further and careful observations.

Pathological Relevance of Anti-Hsp70 IgG Autoantibodies in Epidermolysis Bullosa Acquisita.

Stress-induced heat shock protein 70 (Hsp70) is a key intra- and extracellular molecular chaperone implicated in autoimmune processes. Highly immunogenic extracellular Hsp70 can activate innate and acquired (adaptive) immune responses driving the generation of anti-Hsp70 autoantibodies that are frequently observed in inflammatory/autoimmune disorders. We recently described the direct pathological role of extracellular Hsp70 in epidermolysis bullosa acquisita (EBA), an anti-type VII collagen autoantibody-mediated autoimmune blistering skin disease. Here, we determined the role of anti-Hsp70 autoantibodies in EBA. We observed that circulating anti-Hsp70 IgG autoantibodies were significantly elevated in EBA patients compared to healthy individuals and positively correlated with serum levels of pro-inflammatory interferon gamma (IFN-γ). The pathophysiological relevance of anti-Hsp70 IgG autoantibodies was demonstrated in an antibody transfer-induced EBA mouse model in which elevated serum levels of anti-Hsp70 IgG were found. In addition, anti-Hsp70 IgG-treated animals had a more intense clinical and histological disease activity, as well as upregulated nuclear factor kappa B (NF-κB) activation in skin biopsies compared to isotype-treated animals. Our results suggest that autoantibodies to Hsp70 may contribute to EBA development via enhanced neutrophil infiltration to the skin and activation of the NF-κB signaling pathway in an IFN-γ-associated manner.

Targeting heat shock proteins 90 and 70: A promising remedy for both autoimmune bullous diseases and COVID-19.

Heat shock proteins (Hsps), including Hsp90 and Hsp70, are intra- and extracellular molecules implicated in cellular homeostasis and immune processes and are induced by cell stress such as inflammation and infection. Autoimmune bullous disorders (AIBDs) and COVID-19 represent potentially life-threatening inflammatory and infectious diseases, respectively. A significant portion of AIBDs remain refractory to currently available immunosuppressive therapies, which may represent a risk factor for COVID-19, and suffer from treatment side-effects. Despite advances in vaccination, there is still a need to develop new therapeutic approaches targeting SARS-CoV-2, especially considering vaccine hesitancy, logistical distribution challenges, and breakthrough infections. In this mini review, we briefly summarize the role of targeting Hsp90/70 as a promising double-edged sword in the therapy of AIBDs and COVID-19.

Evidence for a role of extracellular heat shock protein 70 in epidermolysis bullosa acquisita.

Heat shock protein 90 (Hsp90) and Hsp70 are chaperones implicated in different inflammatory disorders, given their property to impact innate and adaptive immune responses. Here, we determined the so far unknown role of extracellular Hsp70 in epidermolysis bullosa acquisita (EBA), an anti-type VII collagen autoantibody-mediated blistering dermatosis. The in vivo pathophysiological relevance of extracellular Hsp70 was demonstrated in an anti-type VII collagen antibody transfer-induced EBA mouse model in which elevated blood levels of this chaperone were recorded. We found that Hsp70-treated mice had a more intense clinical disease severity compared to controls that were paralleled by increased levels of cutaneous matrix metalloproteinase 9 and plasma hydrogen peroxide. The latter finding was confirmed in an independent reactive oxygen species release assay using EBA-specific immune complexes combined with recombinant Hsp70. Finally, cell culture experiments using human naive peripheral blood mononuclear cells (PBMC) revealed that extracellular Hsp70 stimulated the secretion of the T cell-derived pro-inflammatory cytokines IL-6 and IL-8. This work extends knowledge about the role of Hsps in autoimmune bullous diseases, suggesting that extracellular Hsp70 represents a pathophysiological factor and potential treatment target in EBA.

Prevalence and presumptive triggers of localized bullous pemphigoid.

Bullous pemphigoid (BP) is an autoimmune skin disease, caused by autoantibodies to BP180 and/or BP230. While both these autoantigens are expressed in the entire skin, only some parts of the body become affected. Rare clinical observations indicate that BP may also manifest locally, usually following exposure to triggers. Here, we evaluated the occurrence and potential triggers of localized BP (LBP) in a cohort of 285 BP patients. Medical records of all BP patients hospitalized between 2009 and 2019 were reviewed. In 7/285 BP patients, a localized variant was identified. In 5/7 LBP patients, the disease remained local, while in 2/7 patients, an initial LBP subsequently spread. All cases were preceded by presumptive triggers, including previously described triggers and bacterial infections. Overall, LBP is rare. LBP, however, might be underdiagnosed and should thus be considered in the differential diagnosis, particularly when trigger factors preceded.

Therapeutic Implications of Targeting Heat Shock Protein 70 by Immunization or Antibodies in Experimental Skin Inflammation.

Heat shock proteins (Hsp) are constitutive and stress-induced molecules which have been reported to impact innate and adaptive immune responses. Here, we evaluated the role of Hsp70 as a treatment target in the imiquimod-induced, psoriasis-like skin inflammation mouse model and related in vitro assays. We found that immunization of mice with Hsp70 resulted in decreased clinical and histological disease severity associated with expansion of T cells in favor of regulatory subtypes (CD4+FoxP3+/CD4+CD25+ cells). Similarly, anti-Hsp70 antibody treatment led to lowered disease activity associated with down-regulation of pro-inflammatory Th17 cells. A direct stimulating action of Hsp70 on regulatory T cells and its anti-proliferative effects on keratinocytes were confirmed in cell culture experiments. Our observations suggest that Hsp70 may be a promising therapeutic target in psoriasis and potentially other autoimmune dermatoses.

Case Report: Circulating Anti-SARS-CoV-2 Antibodies Do Not Cross-React With Pemphigus or Pemphigoid Autoantigens.

It is hypothesized that SARS-CoV-2 has the potential to elicit autoimmunity due to molecular mimicry between immunogenic proteins of the virus and human extracellular molecules. While in silico and in vitro evaluation of such immune cross-reactivity of human antibodies to SARS-CoV-2 proteins with several different tissue antigens has been described, there is limited information specifically pertaining to the immunological effects of COVID-19 and vaccines against SARS-CoV-2 on the development of autoimmune bullous diseases (AIBDs). Twelve seropositive post-COVID-19 individuals and 12 seropositive healthy volunteers who received two doses of the mRNA COVID-19 vaccine from Pfizer-BioNTech have been included in this case series investigation. Serum samples of these blood donors were tested for autoantibodies to the main immunobullous autoantigens, i.e., desmoglein 1, desmoglein 3, envoplakin, BP180, BP230, and type VII collagen. Our study revealed that none of the 24 anti-SARS-CoV-2 IgG-positive subjects had concomitant antibody reactivity with any of the tested autoantigens. These results argue against a relationship between SARS-CoV-2 infection/vaccines and AIBDs with respect to disease-triggering antibody cross-reactivity.

Covid-19, heat shock proteins, and autoimmune bullous diseases: a potential link deserving further attention.

A link between Covid-19 and development of autoimmunity has been reported. A possible explanation could be molecular mimicry between SARS-CoV-2 and human proteins. Peptide sharing has been found between antigenic epitopes of this virus and heat shock proteins (Hsp) 60 and 90, both of which are associated with autoimmune diseases including those of the bullous type. In particular, there is evidence for the latter Hsp acting as a pathophysiological factor and treatment target in autoimmune blistering dermatoses. Considering multimodal anti-inflammatory mechanisms of action of anti-Hsp90 treatment and drug repositioning results, it may be hypothesized that Hsp90 inhibition could also be a treatment option for cytokine storm-mediated acute respiratory distress syndrome in Covid-19 patients. Hence, although Covid-19-induced autoimmune bullous diseases have not been described in the literature so far, the potential relationship between Covid-19, Hsp, and these autoimmune disorders deserves further attention with respect to both pathophysiology and treatment.

Immunoglobulin and Complement Immunohistochemistry on Paraffin Sections in Autoimmune Bullous Diseases: A Systematic Review and Meta-analysis.

ABSTRACT: Immunohistochemistry (IHC) on formalin-fixed, paraffin-embedded tissue has been proposed as a potential tool in the diagnosis of autoimmune bullous diseases (AIBDs) in lieu of standard direct immunofluorescence (DIF) microscopy. To comprehensively determine the diagnostic accuracy of immunoglobulin and complement IHC for diagnosis of AIBDs, we conducted a systematic review and multivariate Bayesian model-based meta-analysis of the literature. Quality and heterogeneity assessment of studies was performed using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) checklist and the I2 index, respectively. Electronic searches using PubMed from April 1964 to July 2020 identified 14 articles meeting predetermined inclusion and exclusion criteria. Median sensitivities with 95% credible intervals in pemphigus and pemphigoid were 0.24 (0.01-0.89) and 0.22 (0.02-0.77) with immunoglobulin G (IgG), 0.77 (0.39-0.95) and 0.25 (0.02-0.85) with IgG4, 0.11 (0.02-0.32) and 0.86 (0.56-0.98) with C3d, and 0.84 (0.56-0.97) and 0.75 (0.37-0.94) with C4d, respectively. Specificities were 1.00 (0.00-1.00) with IgG, 0.98 (0.89-1.00) with IgG4, 0.99 (0.97-1.00) with C3d, and 0.99 (0.97-1.00) with C4d. The risk of bias and heterogeneity among studies was a serious problem, decreasing the level of evidence. Our work suggests that, in selected cases, paraffin-based IHC may be a helpful procedure to screen for AIBDs, especially when specialized laboratories and/or biopsy specimens for DIF do not exist. Nevertheless, more studies with a refined quality design are needed to explore the true usefulness of this diagnostic method in AIBDs.