Original Article

Journal of Investigative Dermatology Symposium Proceedings (2003) 8, 173–175; doi:10.1046/j.1087-0024.2003.00804.x

Mouse Alopecia Areata Models: An Array of Data on Mechanisms and Genetics

John P Sundberg*,† and Lloyd E King Jr†,‡

  1. *The Jackson Laboratory, Bar Harbor, Maine, USA
  2. †Division of Dermatology Vanderbilt Medical Center, Nashville, Tennessee, USA
  3. ‡Department of Veteran's Affairs, Nashville, Tennessee, USA

Correspondence: John P. Sundberg, The Jackson Laboratory, 600 Main Street, Bar Harbor, ME 04609-1500 USA. Email: jps@jax.org

Received 30 December 2002; Revised 30 December 2002; Accepted 31 January 2003.

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Abstract

Laboratory mice have become the premier animal model for most human and domestic animal diseases, and they have long been the model of choice for studying mammalian genetics, especially since the advent of genetic engineering. Many remarkable discoveries have been made through intense study of these wonderful small mammals, and undoubtably many more will be made.1,2 It is no surprise that one mouse model for alopecia areata (AA) has been found3 possibly many more will be, some of which exhibit rare phenotypes found in subpopulations of humans with the disease, such as nail deformities, thyroid disease, inflammatory bowel disease, and autoimmune polyendocrine syndrome type 14,5 Intense investigation by many groups into the first model, the adult onset form of AA (using the C3H/HeJ inbred strain), found similarities as well as differences with commonly held ideas concerning human AA. Regardless of some of the controversies, much insight has been gained from studying these and other rodent and domestic animal models which has opened up new ideas and discussions of AA and its treatment.

Keywords:

autoimmune disease, lymphocyte costimulatory cascade, alopecia areata review

As with human AA, mice can lose hair only on their head, patchy areas anywhere on their body, or essentially all their hair with prolonged disease. Obvious nail lesions, a rare feature in some humans with AA, are seen only in one congenic strain (McElwee et al, 1999a). Microscopically, anagen-stage hair follicles are targeted in all species affected. A mixed inflammatory response, consisting primarily of T cells, is found in and around the hair follicle. In humans, this is classically found in and around the bulb region; in C3H/HeJ mice, it is found slightly above the bulb. In both species, the inflammation may extend up to the region of the sebaceous gland. In both species the location of the inflammation correlates directly with abnormal expression of major histocompatibility antigens, which explains biologically why there are species-specific morphological differences. The T lymphocytes are primarily CD4+ and CD8+ cells. In humans, the dogma is that CD4+ cells are more prevalent than CD8+ cells. This is a big difference from the mouse, where this ratio can vary with stage of disease. Initial testing of human tissue arrays using antibodies specific for these cell surface markers indicates that the human T cell ratio, as in the mouse, is highly variable between individuals, suggesting that the ratio is not a reliable measure to compare between species. This work is being expanded to domestic animals (Sundberg and King, unpublished data;McElwee et al, 1998b). In both rat and mouse models, depletion or transplantation of either population does not result in full recovery from or causation of disease, suggesting that both populations are involved (McElwee et al, 1996;McElwee et al, 1999b;Carroll et al, 2002). This has been confirmed in a xenograft model (Gilhar et al, 2002). The humoral system has also been implicated in both species, because autoantibodies are present in the sera (Tobin et al, 1994;Tobin et al, 1997). Gene array studies involving both spontaneous human AA and spontaneous or graft-induced mouse AA reveal that the humoral response is very late and nonspecific (Carroll et al, 2002). However, these gene arrays provide evidence supporting activation of the lymphocyte costimulatory cascade.

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The C3H/HeJ Mouse Model

The spontaneous C3H/HeJ mouse model was difficult to use initially because affected mice were found in colonies in relatively low frequency and there was no easy way to determine what stage of disease they were in (waxing or waning of lesions). Breeding studies revealed that this was a complex polygenic trait (Sundberg et al, 1994). Simple skin graft experiments revealed that full-thickness grafts of skin with AA onto histocompatible, clinically normal mice would induce onset of AA in a very predictable manner (McElwee et al, 1998a). This provided both a means to test a variety of hypotheses concerning the mechanisms involved and a more reliable tool to test treatments. Blocking various stages of the lymphocyte costimulatory cascade or surface markers on lymphocytes that are involved with homing to the skin has revealed a general understanding of how lesions evolve (Freyschmidt-Paul et al, 2000b;Carroll et al, 2002). Current ideas for mechanisms involved in the skin graft model are summarized in Figure 1. Briefly, AA is a complex polygenic trait influenced by epigenetic (primarily environmental) events. An antigenic epitope(s), as yet unknown, is recognized by antigen-presenting cells. These cells have B7.1 (CD80) and B7.2 (CD86) lymphocyte costimulatory molecules on their surface. Antigen-presenting cells migrate to regional lymph nodes. A complex of B7.1 and B7.2 ligands and CD28 T cell surface receptors in the presence of antigen signal promotes T cell proliferation, enhances cytokine production, and induces Bcl-x, which promotes T cell survival (Carroll et al, 2002). T Cells with CD44var.10 surface receptors migrate to the skin, homing in on hair follicles in the anagen stage of the hair cycle, thus initiating the first stages of clinical AA (Freyschmidt-Paul et al, 2000b). Subsequent studies confirmed this and that other CD 44 variants are upregulated early and then downregulated. CD44 is not involved with maintenance of disease, and at early stages CD4+/CD25+ regulatory cells are at a low level (McElwee et al, 2002;Zöller et al, 2002).

Figure 1.
Figure 1 - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author

Antigen presenting cells (APCs, Langerhans Cells) with B7.1 and B7.2 surface ligands carry antigenic epitope(s) from the donor skin to draining lymph nodes. These activate lymphocytes with CD28 ligands. Those with CD44.var.10 surface receptors migrate to the skin homing in on anagen stage hair follicles to induce AA at sites distant to the skin graft. Monoclonal antibodies that block these receptors and ligands prevent alopecia areata.

Full figure and legend (21K)

A persistent hypothesis for the pathogenesis of human AA is that melanocytes or melanogenesis-related proteins are the target(s) for the immune system based on the clinical observation that white hair often regrows in human patients and that it is resistant to future recurrences. White hair regrows in grafts from mice with AA onto immunodeficient mice and in some of the spontaneous cases in C3H and B6 hybrids. Induction of white hair by freeze-branding normal mice prior to grafting, in which melanocytes were destroyed, indicated that white hair was not spared and that this observation was the result of injury and a secondary effect (McElwee et al, 2001). This conclusion is supported by the observation of AA-like phenotypes in several albino strains (McElwee et al, 1999a). It should be noted that albino mice (Tyrc) have melanosomes but lack melanin because tyrosinase is not available to convert tyrosine in two steps to dihydroxyphenylalanine-quinone, which ultimately becomes melanin (Kwon et al, 1989). Late upregulation of many melanogenesis-related genes in the mouse graft model also suggests this may be a secondary event in the pathogenesis of AA (Carroll et al, 2002). The Gilhar xenograft model for relapsing AA also recently showed that no single melanocyte antigen is generally associated with AA (Gilhar et al, 2001).

There is ample evidence that human AA has a complicated genetic predisposition (reviewed in Sundberg et al, in press-b). The same is true with the C3H/HeJ mouse model. Crosses between C3H/HeJ mice with AA and C57BL/6J mice that never get this disease were done. Over 1000 F2 females were evaluated. Analyses revealed two regions of interest. The mouse chromosome–17 interval (LOD score 10.9) centers around H2 (human HLA ortholog), but includes a number of other candidate genes. The second interval, on mouse chromosome 9, is only suggestive based on a LOD score of 2.0 (Sundberg et al, 2003).

A major value of the AA mouse graft model is the production of a readily available, reproducible, and predictably induced form of AA in mice for therapeutic screening studies. To date, investigators have found comparable response patterns between mice and humans with AA using intralesional steroids as well as topical applications of diphencyprone, anthralin, and squaric acid dibutyl ester (Sundberg et al, 1994;Freyschmidt-Paul et al, 1999;Shapiro et al, 1999;Gardner et al, 2000). Experimental compounds are now being tested as well (Freyschmidt-Paul et al, 2000a;Tang et al, 2003a,b).

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Summary

The mouse has proven to be another tool with which to dissect the pathogenesis of AA and to investigate new therapeutic approaches. Inbred animals, which include both the mouse and rat models for AA, are essentially identical to each other within a strain and therefore will most likely provide models for very specific subsets of human AA. General comparisons between the very specific rodent diseases and the very pleomorphic human diseases result in misunderstandings of how valuable these models really are. Regardless, data collected from all of the models continue to provide much needed insight on how to deal with human patients with AA.

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Notes

1 Sundberg JP, Bult C. The professional use of mice in hair follicle research. In: Paus R. The Biology of the Hair Follicle. R.G. Landes Company, Austin, TX (in press)

2 Sundberg JP. The laboratory mouse: a biomedical tool that changed the way we think about medicine. Lab Anim (in press).

3 Sundberg JP, Cordy WR, King LE: Alopecia areata in aging C3H/HeJ mice. J Invest Dermatol 102: 847-856, 1994

4 McElwee K Boggess D, Miller J, King L, Sundberg J: Spontaneous alopecia areata-like hair loss in one congenic and seven inbred laboratory mouse strains. J Invest Dermatol Symp Proc 4:202–206, 1999

5 Tazi-Ahnini R, Cork MJ, Gawkrodger DJ, Birch MP, Wengraf D, McDonagh AJG, Messenger AG: Role of the autoimmune regulator (AIRE) gene in alopecia areata: strong association of a potentially functional AIRE polymorphism with alopecia universalis. Tissue Antigens 60:489–495, 2002

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Acknowledgements

The authors thank J.H. Worcester for graphics support. This work was supported by grants from the National Alopecia Areata Foundation (JPS, LEK), the National Institutes of Health (AR43801, RR173, CA34196 to JPS; P30AR41943 to LEK), the Council for Nail Disorders (JPS), and the Veteran's Administration (LEK).

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