Correlation of anti-γ/ε nicotinic acetylcholine receptor antibody levels with anti-desmoglein 1,3 antibody levels and disease severity in pemphigus vulgaris

The Role of Non-Neuronal Acetylcholine in the Autoimmune Blistering Disease Pemphigus Vulgaris

The importance of acetylcholine (ACh) in keratinocyte adhesion and acantholysis has been investigated over the last three decades, particularly in the pathophysiology of autoimmune blistering dermatoses. Pemphigus vulgaris (PV) is an autoimmune blistering skin disease where autoantibody-mediated suprabasilar intraepidermal splitting causes flaccid blisters and non-healing erosions of the oral mucosa and sometimes also of the skin. Historically, acantholysis in PV was thought to be driven by anti-desmoglein (Dsg) antibodies. Herein, we describe the role of autoantibodies against keratinocyte muscarinic and nicotinic acetylcholine receptors, as well as the annexin-like molecule pemphaxin that also binds ACh, in the immunopathogenesis of PV. The identification of targets in this disease is important, as they may lead to novel diagnostic and therapeutic options in the future for this potentially deadly disease.

Effectiveness of topical pilocarpine in refractory oral lesions of pemphigus vulgaris: Results from an open-label, prospective, pilot study

BACKGROUND

The literature suggests a beneficial role of cholinomimetic agents in the treatment of pemphigus. In the present open-label, prospective pilot study, we assessed the effectiveness of topical pilocarpine 2% eye-drops in the treatment of recalcitrant oral lesions of pemphigus.

METHODS

Twenty patients with recalcitrant oral lesions of pemphigus were recruited and instructed to apply pilocarpine 2% eye-drops twice daily on the resistant oral lesions for 180 days. The systemic immunosuppression at the time of inclusion in the present study was continued at the same dose throughout the study duration. The photographs of the lesions were obtained at baseline and an interval of 30 days. The area representing the erosion was measured on clinical photographs using the imageJ software (National Institute of Health). Visual analogue scale and oral health impact profile-14 questionnaire were used to assess the degree of subjective improvement. Anti-desmoglein 1 and 3, and anti-acetylcholine M3 receptor antibodies were measured both in serum and saliva; at baseline and at the completion of the study.

RESULTS

Twenty patients were recruited in this pilot study. Mean total duration of illness was 3.4±1.3 years. The mean area of the erosions decreased significantly from 142.01±130.05 mm2 to 44.38±67.78 mm2 at study completion at 180 days (p 0.002, paired t-test). Repeated measures ANOVA demonstrated a significant trend in the reduction of the mean area of the erosions from baseline to day 180 (p 0.002). Mean VAS decreased significantly from 7.2±1.0 at baseline to 5.1±1.9 at day 180 (paired t-test, p 0.001). Mean OHIP-14 decreased significantly from 10.1±2.7 at baseline to 8.4±2.9 at day 180. No significant difference was observed between pre- and post-treatment levels of anti-desmoglein 1, anti-desmoglein 3, and anti-acetylcholine M3 receptor antibodies, in both serum and saliva.

LIMITATIONS

The depth component in the erosions could not be measured. An orabase formulation could be used in future studies to facilitate retention of the medication at the site of application.

CONCLUSION

Topical pilocarpine holds potential for the treatment of recalcitrant oral lesions of pemphigus vulgaris. It probably brings about re-epithelialization without imparting any immunomodulatory activity. This article is protected by copyright. All rights reserved.

Chronic exposure to the anti-m3 muscarinic acetylcholine receptor autoantibody in pemphigus vulgaris contributes to disease pathophysiology

Pemphigus vulgaris (PV) is a potentially lethal autoimmune mucocutaneous blistering disease characterized by binding of IgG autoantibodies (AuAbs) to keratinocytes (KCs). In addition to AuAbs against adhesion molecules desmogleins 1 and 3, PV patients also produce an AuAb against the M3 muscarinic acetylcholine (ACh) receptor (M3AR) that plays an important role in regulation of vital functions of KCs upon binding endogenous ACh. This anti-M3AR AuAb is pathogenic because its adsorption eliminates the acantholytic activity of PV IgG; however, the molecular mechanism of its action is unclear. In the present study, we sought to elucidate the mode of immunopharmacologic action of the anti-M3AR AuAb in PV. Short-term exposures of cultured KCs to PV IgG or the muscarinic agonist muscarine both induced changes in the expression of keratins 5 and 10, consistent with the inhibition of proliferation and upregulated differentiation and in keeping with the biological function of M3AR. In contrast, long-term incubations induced a keratin expression pattern consistent with upregulated proliferation and decreased differentiation, in keeping with the hyperproliferative state of KCs in PV. This change could result from desensitization of the M3AR, representing the net antagonist-like effect of the AuAb. Therefore, chronic exposure of KCs to the anti-M3AR AuAb interrupts the physiological regulation of KCs by endogenous ACh, contributing to the onset of acantholysis. Since cholinergic agents have already demonstrated antiacantholytic activity in a mouse model of PV and in PV patients, our results have translational significance and can guide future development of therapies for PV patients employing cholinergic drugs.

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.