Immuno-assays

Immuno-assays are helpful serological techniques for the laboratory diagnosis of autoimmune blistering diseases (AIBD) and for monitoring disease activity of individual patients. The three main immuno-assays are immunoblotting, immunoprecipitation and ELISA. All three make use of the ability of the autoimmune IgG to bind to the target antigen. Immunoblotting is used to visualize the apparent molecular mass of the antigen thereby enabling its identification. The same goes for immunoprecipitation that, although being a more laborious technique than immunoblotting, has the advantage that it recognizes more epitopes on the autoantigen than immunoblotting. Whereas immunoblotting and immunoprecipitation are qualitative assays ELISA is a rapid and easy quantitative technique. ELISA therefore enables monitoring of the antibody titer during the disease course. Two recently developed techniques, keratinocyte binding assay and keratinocyte footprint assay are the most sensitive assays for pemphigus and anti-laminin-332 mucous membrane pemphigoid.</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

Non-bullous Lichen Planus Pemphigoides:A Case Report

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Experimental Human Cell and Tissue Models of Pemphigus

Pemphigus is a chronic mucocutaneous autoimmune bullous disease that is characterized by loss of cell-cell contact in skin and/or mucous membranes. Past research has successfully identified desmosomes as immunological targets and has demonstrated that acantholysis is initiated through direct binding of IgG. The exact mechanisms of acantholysis, however, are still missing. Experimental model systems have contributed considerably to today's knowledge and are still a favourite tool of research. In this paper we will describe to what extent human cell and tissue models represent the in vivo situation, for example, organ cultures of human skin, keratinocyte cultures, and human skin grafted on mice and, furthermore, how suitable they are to study the pathogenesis of pemphigus. Organ cultures closely mimic the architecture of the epidermis but are less suitable to answer posed biochemical questions. Cultured keratinocyte monolayers are convenient in this respect, but their desmosomal make-up in terms of adhesion molecules does not exactly reflect the in vivo situation. Reconstituted skin is a relatively new model that approaches organ culture. In models of human skin grafted on mice, acantholysis can be studied in actual human skin but now with all the advantages of an animal model

Keratinocyte Binding Assay Identifies Anti-Desmosomal Pemphigus Antibodies Where Other Tests Are Negative

The serological diagnosis of pemphigus relies on the detection of IgG autoantibodies directed against the epithelial cell surface by indirect immunofluorescence (IIF) on monkey esophagus and against desmoglein 1 (Dsg1) and Dsg3 by ELISA. Although being highly sensitive and specific tools, discrepancies can occur. It is not uncommon that sera testing positive by ELISA give a negative result by IIF and vice versa. This brings diagnostic challenges wherein pemphigus has to be ascertained or ruled out, especially when no biopsy is available. We utilized the ability of anti-Dsg3 and anti-Dsg1 IgG to bind in specific desmosomal patterns to living cells to investigate these discrepancies between IIF and ELISA. Living cultured primary normal human keratinocytes were grown under differentiating conditions to induce adequate expression of Dsg1 and Dsg3, incubated with patient serum for 1 h, and then stained to visualize bound IgG. We investigated two different groups; sera from patients with a positive direct immunofluorescence (DIF) and inconsistent serological findings (n = 43) and sera with positive ELISA or IIF but with negative DIF (n = 60). As positive controls we used 50 sera from patients who fulfilled all diagnostics criteria, and 10 sera from normal human subjects served as negative controls. In the DIF positive group, IgG from 39 of the 43 sera bound to the cells in a desmosomal pattern while in the DIF negative group none of the 60 sera bound to the cells. This shows that for pemphigus patients, ELISA and IIF can be negative while anti-desmosomal antibodies are present and vice versa that ELISA and IIF can be positive in non-pemphigus cases. In absence of a biopsy for DIF, such findings may lead to misdiagnosis

The expression pattern of N-acetyltransferase 1 in healthy human skin

Background N-acetyltransferase 1 (NAT1) is an enzyme expressed among others in keratinocytes in human skin. NAT1 is important in the biotransformation of aromatic amines, an important example being p-phenylenediamine (PPD), a hair dye molecule. Unoxidized PPD penetrates the skin and is N-acetylated by NAT1. Objectives To investigate in detail the expression pattern of NAT1 in human skin. Materials and Methods Cryosections obtained from healthy human skin were stained for NAT1 and expression patterns were observed. NAT1 double stainings were performed with antibodies against different cellular organelles to determine expression patterns. Result A speckled, granular expression of NAT1 was seen predominantly in the stratum basale. NAT1 was expressed in a cytoplasmic pattern, perinuclear, and in the nucleus. No co-localisation was seen with the selected cellular organelles. Local differences in NAT1 expression patterns were observed between donors and between different biopsies obtained from the same donor. Conclusions NAT1 is expressed predominantly in the stratum basale and can be found in the cytoplasm, nucleus, and perinuclear in human skin. Further studies should be performed to investigate expression of NAT1 in a larger sample size