In Vitro, Ex Vivo, and In Vivo Models for the Study of Pemphigus

Abstract

Pemphigus is a life-threatening autoimmune disease. Several phenotypic variants are part of this family of bullous disorders. The disease is mainly mediated by pathogenic autoantibodies, but is also directed against two desmosomal adhesion proteins, desmoglein 1 (DSG1) and 3 (DSG3), which are expressed in the skin and mucosae. By binding to their antigens, autoantibodies induce the separation of keratinocytes, in a process known as acantholysis. The two main Pemphigus variants are Pemphigus vulgaris and foliaceus. Several models of Pemphigus have been described: in vitro, ex vivo and in vivo, passive or active mouse models. Although no model is ideal, different models display specific characteristics that are useful for testing different hypotheses regarding the initiation of Pemphigus, or to evaluate the efficacy of experimental therapies. Different disease models also allow us to evaluate the pathogenicity of specific Pemphigus autoantibodies, or to investigate the role of previously not described autoantigens. The aim of this review is to provide an overview of Pemphigus disease models, with the main focus being on active models and their potential to reproduce different disease subgroups, based on the involvement of different autoantigens.

Keywords: animal model; atypical pemphigus; autoantibodies; autoimmune disease; desmocollin; desmoglein; mucocutaneous pemphigus; pemphigus vulgaris.

Figure 1

Ex vivo and in vitro schematic representations of Pemphigus models. (A) Ex vivo model with human skin organ culture (HSOC) assay. IgG fractions prepared from patients’ sera (PVIgG), or other engineered anti-DSG3 and/or DSG1 antibodies (i.e., scFv), are injected subcutaneously into human healthy skin. Blisters showing the typical histology observed in patients appear after 24 h. (B) In vitro desmosomal cadherins internalization assay in normal human keratinocyte or HaCaT culture monolayers. (C) In vitro with dispase dissociation assay. IgG fractions prepared from patients’ sera (PVIgG), or monoclonal antibodies directed against desmoglein 3 (DSG3) (i.e., AK23) or other engineered anti-desmoglein 3 (DSG3) and/or DSG1 antibodies (scFv), are used in normal human keratinocyte or HaCaT culture monolayers.

Figure 2

In vivo models of Pemphigus. (A) In vivo neonatal passive transfer Pemphigus mouse model. IgG fractions isolated from patients′ sera (PVIgG), or other engineered anti-desmoglein 3 (DSG3) antibodies, are injected subcutaneously or intraperitoneally into new-born mice. Mice develop blisters in 24–36 h, which show the typical histology observed in patients. (B) Active disease model. DSG3^null mice are not tolerant against DSG3 given that DSG3 is never exposed to the immune system. After adoptive transfer of naive lymphocytes from DSG3^null mice, Rag2^−/− immunodeficient mice produce anti-DSG3 IgG antibodies and display traits of PV phenotype. (C) Another active disease model is generated by adoptive transfer of splenocytes after repeated immunization with recombinant DSG3 of a DSG3^null mouse. The receiving Rag2^-/- mouse will develop blisters and hair loss because, in mice, intercellular adhesion of follicular epidermis is mainly mediated by DSG3 during the rest phase of hair growth. (D) Active model after tolerance breakage in a WT mouse with high doses of antigen. After repeated injections, splenocytes were transferred in Rag2^−/− mice, which would develop blisters.