Specific immunoglobulin isotypes correlate with disease activity, morphology, duration and HLA association in Pemphigus vulgaris

Immunohistochemistry for Immunoglobulin G4 on Paraffin Sections as a Diagnostic Test for Pemphigus

ABSTRACT

Pemphigus is a group of autoimmune bullous diseases mediated by autoantibodies most often of the immunoglobulin G class, subclasses immunoglobulin G1, and immunoglobulin G4 (IgG4), directed against desmosomal adhesion proteins of keratinocytes. This study aimed to evaluate IgG4 immunoreactivity on paraffin sections using immunohistochemistry in patients with pemphigus as a diagnostic test. Fifty formalin-fixed paraffin-embedded specimens from patients with pemphigus were selected. Fifty formalin-fixed paraffin-embedded specimens from patients with bullous diseases other than pemphigus were used as controls. Biopsies were performed on active lesions in newly diagnosed patients. Immunohistochemistry for IgG4 was performed on paraffin sections with an anti-immunoglobulin G4 antibody. Positivity was defined as distinctive, uninterrupted immunoreactivity localized to the intercellular junctions of keratinocytes. A finding that did not meet these criteria was defined as negative. Forty-three (86.0%) of the examined patients had pemphigus vulgaris and 7 (14%) had pemphigus foliaceus. Forty-nine (98.0%) specimens from patients with pemphigus were immunoreactive for IgG4, 1 (2%) upper back biopsy from the patient with oral pemphigus showed negative immunoreactivity for IgG4. Negative immunoreactivity was found in 45 (90%) controls. Five (10%) controls with bullous pemphigoid showed immunoreactivity for IgG4. Sensitivity of the method was established to be 98% and specificity 90%. Immunohistochemical examination for IgG4 for the diagnosis of pemphigus can be applied when direct immunofluorescence examination is unavailable. The advantage of this method is that it does not require special equipment and the histology slides are permanent.

HLA class II antigens in Croatian patients with pemphigus vulgaris and their correlation with anti-desmoglein antibodies

Pemphigus vulgaris (PV) is an acquired autoimmune blistering disease characterized by the production of autoantibodies targeting desmosomal cadherins, primarily desmoglein 1 and desmoglein 3, leading to acantholysis. The etiology of PV is multifactorial, including genetic susceptibility. This retrospective study aimed to evaluate the association of HLA class II alleles and PV and to examine the impact of PV-associated HLA class II alleles on the concentration of anti-desmoglein antibodies. The study group included 30 patients in whom the diagnosis of PV was confirmed by histopathological analysis, immunofluorescence findings, and ELISA testing for detecting antibodies against desmoglein 1 and desmoglein 3. HLA class II alleles were typed by polymerase chain reaction with sequence-specific primers (PCR-SSP). The control group consisted of 190 healthy volunteer blood donors. Data analysis revealed a significantly higher frequency of HLA class II alleles in our population of patients with PV, including HLA-DRB1*04:02, HLA-DRB1*14:54, HLA-DQB1*03:02, HLA-DQB1*05:03, HLA- DQA1*03:01, and HLA-DQA1*01:04, as well as a significantly lower frequency of HLA-DQA1*05:01 compared to the control group. We have also investigated the influence of risk alleles for PV, recognized in almost all study populations, HLA-DRB1*04:02 and HLA-DQB1*05:03, on the concentration of antibodies against desmogleins 1 and 3 in relation to the presence of these alleles. The results showed significantly higher levels of antibodies directed against desmoglein 3 among patients with DRB1*04:02 compared to patients without this allele. No difference was found for anti-desmoglein 1 antibodies. Regarding DQB1*05:03 allele, statistical analysis showed no differences in the concentration of anti-desmoglein antibodies in patients carrying this allele versus those without it.

Assessment of tissue E-cadherin and its proteolytic serum fragment in pemphigus vulgaris before and after remission: A case-control study

BACKGROUND

E-cadherin is a classic cadherin that mediates keratinocyte adhesion.

AIMS

To assess the tissue expression of E-cadherin and its proteolytic serum fragment (soluble E-cadherin) in pemphigus vulgaris (PV) before and after clinical remission compared with controls.

PATIENTS

Thirty-seven PV patients and thirty controls were enrolled. Pemphigus disease area index (PDAI) was calculated for patients at baseline and after remission. Punch biopsy specimens were taken from patients before, and after remission, and from controls for assessment of tissue E-cadherin by immunofluorescence. Similarly, serum samples were collected for assessment of serum soluble E-cadherin by ELISA.

RESULTS

Presence, intensity, and mean intensity of tissue E-cadherin were significantly reduced in PV patients before treatment compared with controls (p < 0.001). Detected E-cadherin showed mainly a basal and suprabasal distribution with cell surface and a cytoplasmic expression. Serum E-cadherin was significantly higher in patients before treatment compared with controls (p = 0.006). With remission, tissue E-cadherin presence, intensity, mean intensity, and serum E-cadherin showed statistically significant improvement (p = 0.003, <0.001, <0.001, and 0.003 respectively). Tissue E-cadherin presence and serum E-cadherin level reached values equivalent to the controls (p = 0.49 and 0.44, respectively).

CONCLUSIONS

Disruption of tissue E-cadherin and upregulation of serum soluble E-cadherin can contribute to the pathogenesis of PV. Clinical remission of PV is associated with normalization of tissue and serum E-cadherin.

The Diversity of Serum Anti-DSG3 IgG Subclasses Has a Major Impact on Pemphigus Activity and Is Predictive of Relapses After Treatment With Rituximab

Introduction

We studied the distribution and in vitro pathogenicity of anti-DSG3 IgG subclasses during the course of pemphigus vulgaris (PV).

Methods

We longitudinally studied the distribution of anti-DSG3 IgG subclasses (before versus after treatment) in sera from PV patients, using an addressable-laser bead immunoassay (ALBIA). The in vitro pathogenicity of corresponding sera was tested using keratinocyte dissociation and immunofluorescence assays.

Results

Sixty-five sera were assessed at baseline (33 from patients treated with rituximab and 32 with corticosteroids). Sixty-three percent of these baseline sera contained 2 or more anti-DSG3 IgG subclasses versus 35.7% of sera from patients in complete remission (CR) and 75.0% of sera from patients with persistent disease activity after treatment. IgG4 was the most frequently detected anti-DSG3 IgG subclass, both in patients with disease activity and in those in CR. The presence of three or more anti-DSG3 IgG subclasses was predictive of relapse, in particular when it included IgG3, with a positive predictive value of 62.5% and a negative predictive value of 92%. While anti-DSG3 IgG4 Abs from sera collected before treatment were most often pathogenic, anti-DSG3 IgG4 from sera collected after treatment were pathogenic only after adjusting their titer to the one measured before treatment. The IgG3 fraction containing anti-DSG3 Abs also had an in vitro pathogenic effect. The disappearance of the pathogenic effect of some sera after removal of anti-DSG3 IgG3 suggested an additional effect of this IgG subclass.

Conclusion

The serum levels and number of anti-DSG3 IgG subclasses drive the pathogenic effect of pemphigus sera and may predict the occurrence of relapses.

Current status and prospects for the diagnosis of pemphigus vulgaris

Introduction: Pemphigus vulgaris (PV) is an intraepidermal autoimmune bullous disease (AIBD) characterized by autoantibodies against desmosomal adhesion proteins, most commonly desmoglein (Dsg)3, leading to the suprabasal cleft formation and acantholysis.Areas covered: Direct immunofluorescence (DIF) and indirect immunofluorescence (IIF) studies display the intercellular deposition of IgG/C3 throughout the epidermis and presence of circulating autoantibodies respectively, as a net-like pattern. However, the target antigen remains unknown using immunofluorescence techniques. Thanks to the development of Dsg ELISA, using recombinant technology, circulating antibodies against Dsg1 and 3 could be detected sensitively. It is possible to differentiate PV from pemphigus foliaceus (PF) using this assay. BIOCHIP mosaic and multivariant ELISA are two novel serologic methods with the added value of the ability to screen several AIBDs simultaneously.Non-Dsg1/3 antigens are also involved in the pathogenesis of PV and investigated more deeply thanks to the protein microarrays technique. Additionally, patients with high values of anti-Dsg1/3 may be lesion-free, suggesting the presence of nonpathogenic autoantibodies.Expert opinion: Newer diagnostic methods to replace traditional techniques should possess high sensitivity and specificity and be widely available, noninvasive, and relatively cheap. The newly developed methods need to be further evaluated before being recommended for routine use.

Pemphigus vulgaris disease activity: The role of antibodies to desmogleins and their isotype

BACKGROUND

Pemphigus vulgaris (PV) is an autoimmune blistering disease driven by pathogenic antibodies to desmoglein-1 and -3, levels of which correlate with disease activity. Anti-desmoglein-3 IgG4 isotype antibodies are said to predominate in active disease and anti-desmoglein-3 IgG1 in remission; however, these observations arose from vertical studies, with limited assessments of clinical activity. The objective of this study was to examine the relationship between desmoglein autoantibodies, subdivided by isotype and disease activity using the validated PV activity tool "Pemphigus Disease Area Index (PDAI)."

METHODS

Forty PV patients with predominantly mucosal disease were studied prospectively, 24 serially, and PDAI and anti-desmoglein antibodies recorded at each visit over a period of up to 15 months.

RESULTS

At enrolment, only anti-desmoglein-3 IgG4 levels were significantly associated with disease activity but the correlation was weak. During follow-up, within-patient changes in disease activity correlated with changes in anti-desmoglein-3 IgG levels, but correlations were similar for both anti-desmoglein-3 IgG1 and IgG4. These trends were not observed in anti-desmoglein-1 IgG levels, although the majority of patients were negative at baseline.

CONCLUSIONS

Anti-desmoglein-3 IgG4 levels correlated only weakly with PDAI scores at a single time point. Reciprocity of IgG1 vs IgG4 anti-desmoglein-3 with changes in disease activity over time could not be confirmed, but rather, changes in levels of anti-desmoglein-3 IgG, irrespective of isotype, were useful in following individual patient responses.

Identification of candidate gene FAM183A and novel pathogenic variants in known genes: High genetic heterogeneity for autosomal recessive intellectual disability

The etiology of intellectual disability (ID) is heterogeneous including a variety of genetic and environmental causes. Historically, most research has not focused on autosomal recessive ID (ARID), which is a significant cause of ID, particularly in areas where parental consanguinity is common. Identification of genetic causes allows for precision diagnosis and improved genetic counseling. We performed whole exome sequencing to 21 Turkish families, seven multiplex and 14 simplex, with nonsyndromic ID. Based on the presence of multiple affected siblings born to unaffected parents and/or shared ancestry, we consider all families as ARID. We revealed the underlying causative variants in seven families in MCPH1 (c.427dupA, p.T143Nfs*5), WDR62 (c.3406C>T, p.R1136*), ASPM (c.5219_5225delGAGGATA, p.R1740Tfs*7), RARS (c.1588A>G, p.T530A), CC2D1A (c.811delG, p.A271Pfs*30), TUSC3 (c.793C>T, p.Q265*) and ZNF335 (c.808C>T, p.R270C and c.3715C>A, p.Q1239K) previously linked with ARID. Besides ARID genes, in one family, affected male siblings were hemizygous for PQBP1 (c.459_462delAGAG, p.R153Sfs*41) and in one family the proband was female and heterozygous for X-chromosomal SLC9A6 (c.1631+1G>A) variant. Each of these variants, except for those in MCPH1 and PQBP1, have not been previously published. Additionally in one family, two affected children were homozygous for the c.377G>A (p.W126*) variant in the FAM183A, a gene not previously associated with ARID. No causative variants were found in the remaining 11 families. A wide variety of variants explain half of families with ARID. FAM183A is a promising novel candidate gene for ARID.

The Usefulness of Indirect Immunofluorescence in Pemphigus and the Natural History of Patients With Initial False-Positive Results: A Retrospective Cohort Study

The specificity and the predictive values of indirect immunofluorescence (IIF) in real-life settings is yet to be firmly established. The natural history of patients with false-positive results has not been sufficiently elucidated. The primary aim of the current study is to evaluate the diagnostic value of IIF analysis on monkey esophagus in pemphigus, utilizing a large cohort arising from the real-life experience of a tertiary referral center. The secondary endpoint was to determine the clinical outcomes of patients with false-positive results. This was a retrospective cohort study including all patients who were tested for the presence of intercellular autoantibodies by IIF on monkey esophagus between 2000 and 2017. Overall, 770 sera from different individuals were tested by IIF microscopy. Of those, 176 patients had been diagnosed with pemphigus vulgaris (PV) and 29 patients with pemphigus foliaceus (PF). The sensitivity of this immunoassay was significantly higher for the diagnosis of PV (87.4%; 95% CI, 81.5-91.9%) as compared to PF (69.0%; 95% CI, 49.2-84.7%; P = 0.018). The specificity for the diagnosis of pemphigus was 93.5% (95% CI, 91.1-95.4%). Patients with false-positive results (n = 37) were followed for a median duration of 5.3 years contributing 280.8 person-years. Thirty patients (81.1%) were eventually diagnosed clinically and immunopathologically with subepidermal autoimmune bullous diseases, whereas the remaining patients (18.9%) were diagnosed clinically and histologically with other inflammatory dermatoses, but none of them developed pemphigus during the follow-up duration. Of note, 7.0% (n = 23) of all patients diagnosed with bullous pemphigoid (BP) in the same period (n = 328) were tested positive for IgG intercellular antibodies. Histopathological review of the biopsy specimens of these patients did not reveal acantholysis. In conclusion, the predictive value of negative test in IIF on monkey esophagus is particularly reliable to exclude a diagnosis of pemphigus. Individuals tested positive for intercellular antibodies without an initial overt pemphigus did not show an increased risk for developing pemphigus subsequently. A sizable fraction of patients with BP showed circulating intercellular autoantibodies by IIF, without a histopathological evidence for acantholysis.

Glycans in the immune system and The Altered Glycan Theory of Autoimmunity: a critical review

Herein we will review the role of glycans in the immune system. Specific topics covered include: the glycosylation sites of IgE, IgM, IgD, IgE, IgA, and IgG; how glycans can encode "self" identity by functioning as either danger associated molecular patterns (DAMPs) or self-associated molecular patterns (SAMPs); the role of glycans as markers of protein integrity and age; how the glycocalyx can dictate the migration pattern of immune cells; and how the combination of Fc N-glycans and Ig isotype dictate the effector function of immunoglobulins. We speculate that the latter may be responsible for the well-documented association between alterations of the serum glycome and autoimmunity. Due to technological limitations, the extent of these autoimmune-associated glycan alterations and their role in disease pathophysiology has not been fully elucidated. Thus, we also review the current technologies available for glycan analysis, placing an emphasis on Multiple Reaction Monitoring (MRM), a rapid high-throughput technology that has great potential for glycan biomarker research. Finally, we put forth The Altered Glycan Theory of Autoimmunity, which states that each autoimmune disease will have a unique glycan signature characterized by the site-specific relative abundances of individual glycan structures on immune cells and extracellular proteins, especially the site-specific glycosylation patterns of the different immunoglobulin(Ig) classes and subclasses.

The fibrin-derived citrullinated peptide β60-74Cit₆₀,₇₂,₇₄ bears the major ACPA epitope recognised by the rheumatoid arthritis-specific anticitrullinated fibrinogen autoantibodies and anti-CCP2 antibodies

OBJECTIVES

To evaluate the proportions of rheumatoid arthritis (RA) sera containing anticitrullinated proteins autoantibodies (ACPA) reactive to α36-50Cit₃₈,₄₂ and/or β60-74Cit₆₀,₇₂,₇₄, two peptides identified as bearing the immunodominant epitopes of their major target, citrullinated fibrin. To analyse the relationships of anti-α36-50Cit₃₈,₄₂ and anti-β60-74Cit₆₀,₇₂,₇₄ autoantibodies with autoantibodies reactive to the complete citrullinated human fibrinogen molecule (AhFibA) and with anti-CCP2 antibodies.

METHODS

617 sera from 181 patients with established RA and 436 with non-RA rheumatic diseases were tested by ELISA for AhFibA, anti-CCP2, anti-α36-50Cit₃₈,₄₂, anti-β60-74Cit₆₀,₇₂,₇₄ autoantibodies, and by nephelometry for rheumatoid factor (RF). Diagnostic indexes, correlations and concordances between tests were analysed. Crossreactivity of anti-α36-50Cit₃₈,₄₂ and anti-β60-74Cit₆₀,₇₂,₇₄ autoantibodies was assessed in competition experiments.

RESULTS

At a diagnostic specificity of 95%, the diagnostic sensitivity of AhFibA (83%) was significantly higher than that of all other tests. The diagnostic sensitivity of anti-β60-74Cit₆₀,₇₂,₇₄ (71%) was significantly higher than that of anti-α36-50Cit₃₈,₄₂ autoantibodies (51%) but similar to that of anti-CCP2 (74%). Titres of RF, anti-α36-50Cit₃₈,₄₂ and anti-β60-74Cit₆₀,₇₂,₇₄ autoantibodies were weakly correlated with each other, whereas titres of anti-β60-74Cit₆₀,₇₂,₇₄ were strongly correlated with those of AhFibA (r=0.633) and anti-CCP2 (r=0.634). Anti-α36-50Cit₃₈,₄₂ and anti-β60-74Cit₆₀,₇₂,₇₄ mainly corresponded to two non-crossreactive subfamilies of ACPA. More than 90% of AhFibA-positive or anti-CCP2-positive sera recognised the α36-50Cit₃₈,₄₂ and/or the β60-74Cit₆₀,₇₂,₇₄ peptide.

CONCLUSIONS

Autoantibodies reactive to α36-50Cit₃₈,₄₂ and β60-74Cit₆₀,₇₂,₇₄ form two distinct, non-overlapping subfamilies of ACPA that, together, cover practically all the ACPA reactivity to citrullinated fibrinogen and to CCP2 antigens. In established RA, anti-β60-74Cit₆₀,₇₂,₇₄ autoantibodies show diagnostic indexes similar to those of anti-CCP2.

Molecular diagnosis in autoimmune skin blistering conditions

Blister formation in skin and mucous membranes results from a loss of cell-cell or cell-matrix adhesion and is a common outcome of pathological events in a variety of conditions, including autoimmune and genetic diseases, viral and bacterial infections, or injury by physical and chemical factors. Autoantibodies against structural components maintaining cell-cell and cell-matrix adhesion induce tissue damage in autoimmune blistering diseases. Detection of these autoantibodies either tissue-bound or circulating in serum is essential to diagnose the autoimmune nature of disease. Various immunofluorescence methods as well as molecular immunoassays, including enzyme-linked immunosorbent assay and immunoblotting, belong to the modern diagnostic algorithms for these disorders. There is still a considerable need to increase awareness of the rare autoimmune blistering diseases, which often show a severe, chronic-relapsing course, among physicians and the public. This review article describes the immunopathological features of autoimmune bullous diseases and the molecular immunoassays currently available for their diagnosis and monitoring.

Pemphigus vulgaris autoimmune globulin induces Src-dependent tyrosine-phosphorylation of plakophilin 3 and its detachment from desmoglein 3

The cell adhesion molecule plakophilin 3 (Pkp3) plays an essential role in the maintenance of skin integrity and is targeted in certain autoimmune conditions. In one example, we have shown that Pkp3 is instrumental in mediating the discohesive effects of sera from patients with pemphigus vulgaris (PV), a life-threatening autoimmune disease that targets intercellular adhesion in the epidermis. In the present study, we determine the effect of PV autoimmune globulin (PV IgG) on Pkp3 in an in-vitro model of PV. We demonstrate that Pkp3 becomes tyrosine phosphorylated as early as 30 min upon binding of PV IgG to keratinocyte surface and eventually detaches from its binding partner desmoglein 3 (Dsg3). In parallel, Pkp3 is depleted from the membrane (Triton X-soluble) fraction and accumulates in the cytoplasm within 240 min of incubation with PV IgG. Inhibition of Pkp3 phosphorylation by a Src inhibitor attenuates the discohesive effects of PV IgG. Taken together, the data demonstrate that activation of Src-kinase signalling is crucial for PV acantholysis and acts, at least in part, via phosphorylation of the adaptor protein Pkp3.