A "hair-raising" history of alopecia areata

A 3500-year-old papyrus from ancient Egypt provides a list of treatments for many diseases including "bite hair loss," most likely alopecia areata (AA). The treatment of AA remained largely unchanged for over 1500 years. In 30 CE, Celsus described AA presenting as scalp alopecia in spots or the "windings of a snake" and suggested treatment with caustic compounds and scarification. The first "modern" description of AA came in 1813, though treatment still largely employed caustic agents. From the mid-19th century onwards, various hypotheses of AA development were put forward including infectious microbes (1843), nerve defects (1858), physical trauma and psychological stress (1881), focal inflammation (1891), diseased teeth (1902), toxins (1912) and endocrine disorders (1913). The 1950s brought new treatment developments with the first use of corticosteroid compounds (1952), and the first suggestion that AA was an autoimmune disease (1958). Research progressively shifted towards identifying hair follicle-specific autoantibodies (1995). The potential role of lymphocytes in AA was made implicit with immunohistological studies (1980s). However, studies confirming their functional role were not published until the development of rodent models (1990s). Genetic studies, particularly genome-wide association studies, have now come to the forefront and open up a new era of AA investigation (2000s). Today, AA research is actively focused on genetics, the microbiome, dietary modulators, the role of atopy, immune cell types in AA pathogenesis, primary antigenic targets, mechanisms by which immune cells influence hair growth, and of course the development of new treatments based on these discoveries.

What Can We Learn from Animal Models of Alopecia areata?

Alopecia areata (AA) is a hair loss disease marked by a focal inflammatory infiltrate of dystrophic anagen stage hair follicles by CD4+ and CD8+ lymphocytes. Although AA is thought to be an autoimmune disorder, definitive proof is lacking. Moreover, characterization of the primary pathogenic mechanisms by which hair loss is induced in AA is limited. In this context, animal models may provide a vital contribution to understanding AA. Recent research using animal models of AA has focused on providing evidence in support of a lymphocyte-mediated pathogenic mechanism consistent with AA as an autoimmune disease. In the future, research with both humans and animal models shall likely concentrate on identifying the primary antigenic epitopes involved in AA and the genetics of AA susceptibility. With a comprehensive understanding of the key elements in AA pathogenesis, new avenues for therapeutic research and intervention will be defined.

A natural canine homologue of alopecia areata in humans

BACKGROUND

Alopecia areata (AA) is suspected to be an autoimmune disease directed preferentially against hair follicles (HF) affecting both humans and various mammalian species. Recently, two rodent models of AA were described, namely the ageing C3H/HeJ mouse and the DEBR rat. Despite several case reports of canine AA in the literature, there has been no systematic assessment of the disease in these companion animals, and it is also not known whether dogs with AA could be useful as an outbred homologue of this disease in humans.

OBJECTIVES

To evaluate the clinical, histopathological and immunopathological features of 25 dogs with AA and compare these data with those found in the human disease.

PATIENTS/METHODS

Twenty-five client-owned dogs exhibiting macroscopic alopecia with peri- or intrabulbar lymphocytic infiltrates were selected for study. Biopsies and sera were obtained and assessed by histopathology, direct immunofluorescence of immunoreactant deposition, immunohistochemistry for lymphocyte markers, indirect immunofluorescence and immunoblotting analysis of circulating serum IgG, selective immunoprecipitation of HF proteins by serum IgG, and passive transfer of purified canine IgG into naïve C57BL/10 mice.

RESULTS

Clinical signs including alopecia, skin hyperpigmentation and leucotrichia usually developed during adulthood and were first seen on the face, followed by the forehead, ears and legs. Spontaneous remission of alopecia occurred in 60% of dogs and regrowing hair shafts were often non-pigmented. Histological examination of skin biopsy specimens revealed peri- and intrabulbar mononuclear cell infiltrates affecting almost exclusively anagen HF. Direct immunofluorescence analysis detected HF-specific IgG in 73% of dogs, while indirect immunofluorescence revealed circulating IgG autoantibodies to the HF inner and outer root sheaths, matrix and precortex. Immunoblotting analysis revealed IgG reactivity to proteins in the 45-60 kDa molecular weight range and with a 200-220 kDa doublet. The latter was identified as trichohyalin by selective immunoprecipitation. Purified HF-reactive IgG, pooled from AA-affected dogs, was injected intradermally to the anagen skin of naïve mice where it was associated with the local retention of HFs in an extended telogen phase in AA-treated skin compared with that seen in controls.

CONCLUSIONS

These findings are very similar to those reported for human AA patients; therefore, they support the consideration of dogs with AA as a useful homologue for the study of the pathogenesis of this common autoimmune disease of humans.

Alopecia areata - animal models

Several rodent models with spontaneous and induced alopecia areata (AA), a nonscarring inflammatory hair loss disease with suspected autoimmune elements, have been identified. Of these, the C3H/HeJ mouse and DEBR rat have been most extensively used in examining AA development. Flow cytometry and micro array characterization, manipulation of inflammatory cells by in vivo cell depletion or cell receptor blockade, lymph node cell transfer between affected and unaffected rodents, and the recent use of transgenic knockout mice have given important insights into the development of AA. From our current understanding of rodent models, the development of AA relies upon a general genetic susceptibility where major susceptibility genes may be supplemented by minor disease severity modifying genes. However, the actual onset of AA, its duration, extent, and persistence in individual rodents may be modified by epigenetic factors. Rodent AA seems to be fundamentally, but not exclusively, Th1 cell mediated. Onset of disease may be dependent on several factors including the break down of the putative anagen stage hair follicle immune privilege, appropriate antigen presentation with costimulation of lymphocytes, presence of autoreactive lymphocytes, and a deficiency of functional immune system regulatory cells. Rodents have already been used in examining a variety of current AA treatments and developing new therapies with some success. With a greater understanding of AA disease mechanisms through rodent model research, improved and more specific treatment interventions may be defined.

Alopecia areata: an autoimmune disease?

A wide range of hypotheses such as focal infection, trophoneuroses, and endocrine dysfunction, have been previously proposed to explain the pathogenesis of alopecia areata (AA). Currently, the most widely held belief is that AA is an autoimmune disease with cellular and/or humoral immunity directed against anagen hair follicle antigen(s). However, until recently evidence in support of an autoimmune mechanism of AA has been largely circumstantial. More fundamental evidence has recently been amassed in support of AA as an autoimmune disease by using animal models. These data include: 1) identification of cross-species hair follicle specific IgG autoantibodies, 2) The ability to induce AA in an animal model with transfer of skin from affected to naive individuals, and 3) the induction of disease by transfer of lymphocytes to human skin grafted to severe combined immunodeficiency mutant mice. A review of the previous and current data related to the autoimmune basis of AA is provided to put into perspective the future studies needed to definitively determine whether AA is an autoimmune disease.

Topical FK506: a potent immunotherapy for alopecia areata? Studies using the Dundee experimental bald rat model

We elected to examine the efficacy of the topically applied immunosuppressive agent FK506 (Prograf) in the treatment of alopecia areata (AA) using the Dundee experimental bald rat (DEBR) model. Thirty lesional DEBR rats were allocated to five groups of six. Group 1 rats received 0.1 mL of a 0.25% solution of FK506 within a 2 x 2 cm marked area on one bald flank twice a week (125 micrograms FK506/cm2 per week) for 8 weeks, while the contralateral flank was left untreated. In group II, 0.05 mL of a 0.1% solution of FK 506 was applied 5 days per week on one flank (62.5 micrograms FK506/ cm2 per week) and control vehicle to the opposite flank for 8 weeks. Group III rats were treated as in group II except that drug and vehicle were applied twice a week (25 micrograms FK506/cm2 per week) for 4 weeks. A positive control group received orally administered cyclosporin A (CsA) (10 mg/kg daily) for 8 weeks and a further group was left untreated. Rats were regularly examined and photographed with skin biopsies taken from groups II and III. All FK 506-treated rats regrew hair at the site of drug application within 14-21 days. Growth continued for 3 weeks beyond termination of treatment after which gradual hair loss was observed. No hair growth was seen as a result of vehicle application and hair loss continued on untreated areas and in the untreated control group. Immunohistology revealed a drastic reduction in the follicular inflammatory infiltrate at the site of the FK506 application. The oral CsA group responded by simultaneous regrowth of hair over the whole body. Our findings suggest that FK506 may have considerable potential as a topical treatment for AA.