Alopecia areata. Autoreactive T cells are variably enriched in scalp lesions relative to peripheral blood

What causes alopecia areata?

The pathobiology of alopecia areata (AA), one of the most frequent autoimmune diseases and a major unsolved clinical problem, has intrigued dermatologists, hair biologists and immunologists for decades. Simultaneously, both affected patients and the physicians who take care of them are increasingly frustrated that there is still no fully satisfactory treatment. Much of this frustration results from the fact that the pathobiology of AA remains unclear, and no single AA pathogenesis concept can claim to be universally accepted. In fact, some investigators still harbour doubts whether this even is an autoimmune disease, and the relative importance of CD8(+) T cells, CD4(+) T cells and NKGD2(+) NK or NKT cells and the exact role of genetic factors in AA pathogenesis remain bones of contention. Also, is AA one disease, a spectrum of distinct disease entities or only a response pattern of normal hair follicles to immunologically mediated damage? During the past decade, substantial progress has been made in basic AA-related research, in the development of new models for translationally relevant AA research and in the identification of new therapeutic agents and targets for future AA management. This calls for a re-evaluation and public debate of currently prevalent AA pathobiology concepts. The present Controversies feature takes on this challenge, hoping to attract more skin biologists, immunologists and professional autoimmunity experts to this biologically fascinating and clinically important model disease.

Chronic delayed-type hypersensitivity reaction as a means to treat alopecia areata

The acute phase of alopecia areata (AA) is characterized by an increase in CD44v3+ and CD44v10+ skin-infiltrating leucocytes (SkIL). Induction of a contact eczema, one of the therapeutic options in AA, can be mitigated strongly by a blockade of CD44v10. The observation that induction of a delayed type hypersensitivity (DTH) reaction abrogates an autoimmune reaction, where both responses apparently use similar effector mechanisms, is surprising and prompted us to search for the underlying mechanisms. AA-affected C3H/HeJ mice were treated with the contact sensitizer SADBE (squaric acid dibutylester) and leucocyte subpopulations and their activation state was evaluated in SkIL and draining lymph nodes. AA-affected mice exhibited an increased number of SkIL with a predominance of T lymphocytes. After treatment with the contact sensitizer SADBE recovery of SkIL was reduced and monocytes predominated. However, a significantly increased number of leucocytes was recovered from draining lymph nodes. Draining lymph node cells from untreated and treated AA mice exhibited all signs of recent activation with high-level expression of co-stimulatory and accessory molecules and an increased percentage of CD44v3+ and CD44v10+ leucocytes. In contrast, SkIL of SADBE-treated AA mice contained relatively few activated T cells and reduced numbers of CD44v3+ and CD44v10+ cells. Thus, the activation state and the distribution of leucocyte subsets in SADBE-treated AA mice are consistent with a blockade of leucocyte extravasation. Accordingly, the therapeutic effect of long-term SADBE treatment may rely on impaired leucocyte traffic.

Autoimmune hair loss induced by alloantigen in C57BL/6 mice

Exponentially growing Meth-A cells expressing H-2K(d).D (d) antigen were found to induce alopecia when injected intraperitoneally into normal C57BL/6 mice, which express the H-2K(b).D (b) antigen. However, the capacity to induce alopecia disappeared when Meth-A cells were treated with K252a, which inhibits protein kinases. Histologically, skin in affected areas showed dense mononuclear cell infiltration and a focal foreign-body giant-cell reaction in hair follicles. The subtyping of lymphocytes in peripheral blood demonstrated a significant difference between normal mice and Meth-A cell-injected mice. To further examine the mechanism by which the alloantigen induces alopecia, lymphocytes isolated from the peripheral blood of normal C57BL/6 mice were cultured in medium containing Meth-A cell homogenate, phytohemagglutinin (PHA) and recombinant mouse interleukin-2 (rm IL-2), and intravenously injected into normal C57BL/6 mice. The adoptive transfer of the lymphocytes induced alopecia in a similar way. These findings suggest that the protein kinase-modulated alloantigen induces alopecia by disturbing the immunological homeostasis, and that lymphokine-activated killer cells play an important role in induction of alopecia by cross-reacting with hair follicles.

Thyroid function, autoantibodies, and HLA tissue typing in children with alopecia areata

A total of 80 Kuwaiti children with alopecia areata (AA), without clinical evidence of thyroid disease, were screened for the presence of thyroid abnormalities, and 50 unrelated children with AA were tissue typed for human leukocyte antigen (HLA) class I and class II antigens. Thyroid abnormalities were detected in 14 children (17.5%). Among these, 11 children (14%) had thyroid autoantibodies. These observations highlight the significance of screening for thyroid abnormalities in children with chronic, recurrent, and/or extensive disease. The Kuwaiti children with AA were observed to have a significant association with HLA B21 (OR 18.850, 95% CI 4.404-80.677), B40 (OR 6.767, 95% CI 1.818-25.181), and HLA B12 (OR 4.833, 95% CI 1.198-19.505) antigens. These findings differed from those reported elsewhere.

Association analysis of IL1A and IL1B variants in alopecia areata

Alopecia areata is an inflammatory hair loss disease with a major genetic component. The disease is characterized by focal inflammatory lesions with perifollicular T-cell infiltrates, reflecting the role of local cytokine production in the development of patchy hair loss. IL-1 alpha and IL-1 beta are important inhibitors of hair growth in vitro. Their effect is opposed by the interleukin-1 receptor antagonist, IL-1ra. Genes of the IL-1 cluster are candidate genes in the pathogenesis of alopecia areata. To investigate the role of the IL-1 system in alopecia areata we examined three biallelic polymorphisms within the IL-1 gene cluster (IL1A+4845, IL1B+3954 and IL1B-511) in 165 patients and a large number of matched controls (n=1150). There was no significant association of IL1B-511 or IL1B+3954 genotypes with the overall dataset, or with disease severity or age at onset, in contrast with a previous report. The results suggested the possibility of an association with IL1A+4845 in the overall dataset [OR 1.39 (95% CI 1.00, 1.93)] although this was not statistically significant. This was due mainly to the contribution from mild cases of alopecia areata [OR 1.48 (0.96, 2.29)], suggesting that IL-1 alpha may have a particular role in the pathogenesis of this subgroup.

Acquired scalp alopecia. Part I: A review

In this two-part series we review the acquired scalp alopecias. A broad spectrum of diseases result in alopecia. In this first part we provide a framework for the assessment and diagnosis of scalp hair loss, and begin covering the individual conditions. The non-scarring alopecias covered include effluvium, androgenetic alopecia, alopecia areata, trichotillomania, and loose anagen syndrome. The scarring alopecias cause permanent pilosebaceous follicle loss; the lymphocyte-associated scarring alopecia described encompasses lichen planopilaris, discoid lupus erythematosus, pseudopelade, and follicular mucinosis. Part II will cover the neutrophil-associated and infiltrative processes causing scarring alopecia followed by the medical management of alopecia. There is particular reference to newly described conditions and progress in the understanding of older conditions. More recently characterized conditions include the loose anagen syndrome, chronic telogen effluvium, and the frontal fibrosing variant of lichen planopilaris.

Autoimmune hair loss (alopecia areata) transferred by T lymphocytes to human scalp explants on SCID mice

Alopecia areata is a tissue-restricted autoimmune disease of the hair follicle, which results in hair loss and baldness. It is often psychologically devastating. The role of T lymphocytes in this disorder was investigated with cell transfer experiments. Scalp explants from patients were transplanted to severe combined immunodeficiency (SCID) mice and injected with autologous T lymphocytes isolated from involved scalp. T lymphocytes which had been cultured with hair follicle homogenate along with antigen-presenting cells were capable of inducing the changes of alopecia areata, including hair loss and perifollicular infiltrates of T cells, along with HLA-DR and ICAM-1 expression of the follicular epithelium. Similar changes were not noted in grafts injected with scalp-derived T cells that had not been cultured with follicular homogenate. These data indicate that alopecia areata is mediated by T cells which recognize a follicular autoantigen.

The aetiology and pathogenesis of alopecia areata

In common with a number of inflammatory autoimmune diseases, genetic factors including HLA class II associations have been identified in alopecia areata. No consensus has been reached on the identity of a specific disease target within the hair follicle in alopecia areata. Suggested candidate cell types include the dermal papilla cells, the keratinocytes of the matrix and presumptive cortex and the hair bulb melanocytes, but these need not be mutually exclusive. The pathogenesis is known to involve disturbance of immune function but there is no proof that an autoimmune mechanism is fundamental. We propose a pathogenetic model incorporating polygenic determination of disease susceptibility and severity with additional, possibly environmental, factors as triggers for disease expression.