Basic principles of the immune system and autoimmunity

The immune system is composed of two closely collaborative systems, an innate and an adaptive system. The innate immune system is a constitutive present system that can act rapidly to eradicate microbes. The primary cells of the innate immune system are macrophages, granulocytes, natural killer cells and dendritic cells. The adaptive system can be divided in a humoral and cellular response. The humoral response is characterized by activation of B-lymphocytes with subsequent maturation into plasma cells and production of antibodies, whereas a cellular immune response is characterized by transformation of T-lymphocytes into cytotoxic T-cells, capable of killing virally infected cells. Auto-reactive B- and T-lymphocytes can induce autoimmune diseases. Autoimmune blistering diseases are the result of type II hypersensitivity, e.g. autoantibodies are directed against cell or matrix components. In pemphigoid diseases antibodies are directed against hemidesmosomal components, whereas pemphigus is characterized by antibodies against desmosomal proteins.</p

Direct immunofluorescence microscopy

Direct immunofluorescence plays an important role in the diagnosis of autoimmune blistering diseases. The purpose of direct immunofluorescence microscopy is to detect in vivo antibodies in patient's skin or mucosa. Direct immunofluorescence of pemphigus shows depositions of immunoglobulins and/or complement on the epithelial cell surface of keratinocytes, whereas pemphigoid shows linear deposition of immunoglobulins along the epidermal basement membrane zone. This linear deposition can be separated in an n-serrated pattern and a u-serrated pattern. An n-serrated pattern is seen in blistering diseases with binding above the lamina densa with antibodies against hemidesmosomal components, e.g. bullous pemphigoid, while a u-serrated pattern points to a sublamina densa binding diseases caused by autoantibodies against type VII collagen, e.g. epidermolysis bullosa acquisita. Finally, dermatitis herpetiformis shows a granular IgA deposition along the epidermal basement membrane zone.</p

Indirect immunofluorescence microscopy

The purpose of indirect immunofluorescence microscopy is to detect circulating antibodies in patient's serum. For this purpose an adequate substrate is necessary to visualize these antibodies. Monkey esophagus is the most widely used substrate for detecting of circulating autoantibodies in patients with autoimmune blistering diseases. In all variants of pemphigus antibodies show an epithelial cell surface pattern, resulting from present autoantibodies against the desmosomal molecules desmoglein 1 and/or 3. This pattern is also called chicken wire or honeycomb pattern. In pemphigoid a linear deposition along the epithelial basement membrane can be observed, caused by autoantibodies against hemidesmosomes or their connecting proteins underneath. Human salt split skin is a valuable substrate in the diagnosis of subepidermal autoimmune blistering diseases. Important antigens in the roof of salt split skin are type XVII collagen (BP180) and BP230, whereas laminin 332, p200 and type IV collagen are situated in the floor of the blister. This implies that bullous pemphigoid, mucous membrane pemphigoid, pemphigoid gestationis, and lichen planus pemphigoides show staining of IgG on the epidermal side of the blister. On the other hand anti-laminin 332 pemphigoid, anti-p200 pemphigoid, epidermolysis bullosa acquisita, and bullous SLE show staining on the dermal side. Other less used, but valuable substrates in some instances, are rat bladder and knock-out skin.</p

How to take a biopsy

The skin is an organ that is easy to access for microscopy. Sections of the skin may reveal the split level of the blister, the type and distribution of inflammatory cells, and the presence, class and distribution pattern of autoantibodies. A biopsy should be taken from a location with smallest change of sample error, and the specimen specially fixated and transported for the requested microscopic techniques. Taking biopsies is the area of expertise of the dermatologist, even taking conjunctiva biopsies for immunofluorescence (IF) is possible in cases of suspicion of an autoimmune blistering disease of the eye.</p

Paraneoplastic pemphigus

Paraneoplastic pemphigus is a rare but severe potentially fatal autoimmune disease characterized by severe stomatitis and a variety of cutaneous manifestations in association with an underlying neoplasia. Pulmonary involvement may also occur. The pathogenesis involves the production of autoantibodies against desmogleins, plakins and the protease inhibitor alpha-2 macroglobuline like-1, but T-cell mediated autoimmunity is also thought to play a role. Diagnosis usually relies on the demonstration of a specific subset of circulating autoantibodies in patient serum, although in a small subset of patients these autoantibodies might be absent. Due to it's rarity, there are no guidelines for the treatment of PNP. The general approach includes a variety of immunosuppressive agents and treatment of the underlying neoplasia. Despite treatment, paraneoplastic pemphigus has high mortality rates, often due to sepsis, respiratory failure or progression of the underlying malignancy.</p

Evaluation of Nomacopan for Treatment of Bullous Pemphigoid:A Phase 2a Nonrandomized Controlled Trial

Importance: Bullous pemphigoid is a difficult-to-treat autoimmune blistering skin disease that predominantly affects older adults and is associated with an increased mortality rate. Objective: To examine the safety and therapeutic potential of nomacopan, an inhibitor of leukotriene B4and complement C5, in patients with bullous pemphigoid. Design, Setting, and Participants: This multicenter, single-group, phase 2a nonrandomized controlled trial was conducted in the dermatology departments of universities in the Netherlands and Germany. Participants were enrolled between September 2018 and April 2020. Older adult patients (aged ≥55 years) with mild to moderate, new-onset or relapsing bullous pemphigoid were recruited into the study. Interventions: Patients received nomacopan, 90 mg, subcutaneously on day 1 and 30 mg subcutaneously daily until day 42. Main Outcomes and Measures: The primary end point was the proportion of patients with grade 3 to 5 (severe) adverse events associated or possibly associated with nomacopan. Secondary end points included mean absolute and percentage changes in the Bullous Pemphigoid Disease Area Index (BPDAI) activity score, the BPDAI pruritus score, and the patient-reported outcome measures Dermatology Life Quality Index (DLQI) and Treatment of Autoimmune Bullous Disease Quality of Life (TABQOL). Results: A total of 9 patients (median [range] age, 75 [55-85] years) with bullous pemphigoid were included in the trial, of whom 5 were women (55.6%). No serious adverse events associated with nomacopan were found. The mean (90% CI) BPDAI activity score decreased from 32.0 (8.7) points on day 1 to 19.6 (9.0) points on day 42. Seven of 9 patients (77.8%) responded to nomacopan with a reduction in the BPDAI activity score of at least 8 points between days 1 and 42; in 3 responders, the reduction was 80% or greater. On day 42, the mean (90% CI) BPDAI pruritus score had decreased by 6.8 (4.6) points from 17.6 (4.0) points on day 1. The mean (90% CI) DLQI score decreased from 11.3 (4.2) points at baseline to 6.4 (3.8) points by day 42, and the mean (90% CI) TABQOL score decreased from 14.6 (5.4) points at baseline to 10.3 (5.0) points on day 42. Conclusions and Relevance: Results of this nonrandomized controlled trial suggest that nomacopan can be well tolerated in older patients with bullous pemphigoid and may have therapeutic benefits for suppressing acute flares of this disease. A larger, placebo-controlled randomized clinical trial is warranted to confirm this safety profile and to establish nomacopan as a new therapeutic option for bullous pemphigoid. Trial Registration: ClinicalTrials.gov Identifier: NCT04035733

Diagnostic Utility of C4d by Direct Immunofluorescence in Bullous Pemphigoid

ABSTRACT: Bullous pemphigoid (BP) is an autoimmune blistering disease that commonly affects elderly patients. Direct immunofluorescence (DIF) for immunoglobulin G (IgG) and C3c on frozen skin biopsies is the gold standard for the diagnosis of BP. In a minority of cases, IgG and/or C3c are found negative, and in these situations, there is a need for a more stable diagnostic marker of BP. C4d is biologically inactive, but has a long half-life, rendering it a long-lived marker for antibody-mediated complement activation. Previous studies already demonstrated that C4d was diagnostically useful in formalin-fixed paraffin-embedded skin biopsies of patients with BP. We hypothesized that C4d detected by DIF could also be a promising diagnostic marker for BP, particularly in IgG and/or C3c DIF-negative cases. In this single-center retrospective study, 69 cases of BP were analyzed for linear deposition of C4d; of the 69 cases, n = 26 were IgG+/C3c-, n = 10 IgG+/C3c+, and n = 33 IgG-/C3c-. Results were compared with n = 39 negative controls. Seven of the 26 (27%) IgG+/C3c- and 3 of the 33 (9%) IgG-/C3c- BP cases were positive for C4d. All 10 IgG+/C3c+ cases were also C4d positive. In the negative control group, 2 of the 39 (5%) were found positive for C4d. In conclusion, the current study shows that C4d is a more sensitive but not a 100% specific marker of BP. We conclude that C4d by DIF could be an interesting diagnostic adjunct for BP, particularly in IgG-/C3c- double negative cases