Alopecia areata (AA) is among the most highly prevalent human autoimmune diseases, leading to disfiguring hair loss due to the collapse of immune privilege of the hair follicle and subsequent autoimmune attack1,2. The genetic basis of AA is largely unknown. We undertook a genome-wide association study (GWAS) in a sample of 1,054 cases and 3,278 controls and identified 139 single nucleotide polymorphisms that are significantly associated with AA (P ≤ 5 × 10 −7 ). Here we show © 2010 Macmillan Publishers Limited. All rights reservedCorrespondence and requests for materials should be, addressed to A.M.C. (amc65@columbia.edu). Supplementary Information is linked to the online version of the paper at www.nature.com/nature.Author Contributions L.P. performed technical aspects in preparation of samples for genotyping, the statistical analysis and preparation of the manuscript. M.D., V.P., M.H. and D.N. participated in phenotyping, diagnosis, and access to patient samples from the National Alopecia Areata Registry. Y.S., P.S. and H.K. provided expertise in RT-PCR and immunofluorescence. K.C.M. and R.P. provided expertise in immunhistochemistry. A.L. and P.K.G. provided control samples and performed genotyping as well as insight into autoimmune diseases. W.V.C. and C.I.A. provided additional statistical analysis and control samples from a distinct cohort. C.A.B.J. performed hair follicle microdissection and provided indispensable scientific expertise on the dermal sheath. A.M.C. provided oversight and conceptual guidance to the project, input into the functional significance of candidate genes, supervision of laboratory personnel, management of collaborations, preparation of the manuscript and all reporting requirements for granting agencies.Reprints and permissions information is available at www.nature.com/reprints.The authors declare no competing financial interests.Readers are welcome to comment on the online version of this article at www.nature.com/nature. NIH Public Access Author ManuscriptNature. Author manuscript; available in PMC 2011 January 1. PRDX5 and STX17). A region of strong association resides within the ULBP (cytomegalovirus UL16-binding protein) gene cluster on chromosome 6q25.1, encoding activating ligands of the natural killer cell receptor NKG2D that have not previously been implicated in an autoimmune disease. By probing the role of ULBP3 in disease pathogenesis, we also show that its expression in lesional scalp from patients with AA is markedly upregulated in the hair follicle dermal sheath during active disease. This study provides evidence for the involvement of both innate and acquired immunity in the pathogenesis of AA. We have defined the genetic underpinnings of AA, placing it within the context of shared pathways among autoimmune diseases, and implicating a novel disease mechanism, the upregulation of ULBP ligands, in triggering autoimmunity.AA affects about 5.3 million people in the United States alone, including males and females across all ethnic groups, with a lifetime risk ...

Lichen planopilaris (LPP) is a chronic inflammatory disease of unknown pathogenesis that leads to permanent hair loss. Whilst destruction of epithelial hair follicle stem cells (eHFSCs) that reside in an immunologically protected niche of the HF epithelium, the bulge, is a likely key event in LPP pathogenesis, this remains to be demonstrated. We have tested the hypotheses that bulge immune privilege (IP) collapse and inflammation-induced eHFSC death are key components in the pathogenesis of LPP. Biopsies of lesional and non-lesional scalp skin from adult LPP patients (n = 42) were analysed by quantitative (immuno)histomorphometry, real-time quantitative polymerase chain reaction (qRT-PCR), laser capture microdissection and microarray analysis, or skin organ culture. At both the protein and transcriptional level, lesional LPP HFs showed evidence for bulge IP collapse (ie increased expression of MHC class I and II, β2microglobulin; reduced TGFβ2 and CD200 expression). This was accompanied by a Th1-biased cytotoxic T cell response (ie increased CD8(+) GranzymeB(+) T cells and CD123(+) plasmacytoid dendritic cells, with increased CXCR3 expression) and increased expression of interferon-inducible chemokines (CXCL9/10/11). Interestingly, lesional LPP eHFSCs showed both increased proliferation and apoptosis in situ. Microarray analysis revealed a loss of eHFSC signatures and increased expression of T cell activation/binding markers in active LPP, while bulge PPARγ transcription was unaltered compared to non-lesional LPP HFs. In organ culture of non-lesional LPP skin, interferon-γ (IFNγ) induced bulge IP collapse. LPP is an excellent model disease for studying and preventing immune destruction of human epithelial stem cells in situ. These novel findings raise the possibility that LPP represents an autoimmune disease in whose pathogenesis IFNγ-induced bulge IP collapse plays an important role. Therapeutically, bulge IP protection/restoration may help to better manage this highly treatment-resistant cicatricial alopecia.

These data suggest that the bulge of human anagen HFs represents a hitherto unrecognized site of relative IP in human skin. Simultaneously, we present the first evidence of IDO and HLA-E protein expression in normal human HFs. Bulge IP presumably protects the HF epithelial stem cell reservoir from autoaggressive immune attack whereas a loss of bulge IP may play a central role in the pathogenesis of cicatricial alopecias.

Context: Both insufficient and excess levels of thyroid hormones (T 3 and T 4 ) can result in altered hair/skin structure and function (e.g. effluvium). However, it is still unclear whether T 3 and T 4 exert any direct effects on human hair follicles (HFs), and if so, how exactly human HFs respond to T 3 /T 4 stimulation.Objective: Our objective was to asses the impact of T 3 /T 4 on human HF in vitro. Methods:Human anagen HFs were isolated from skin obtained from females undergoing facelift surgery. HFs from euthyroid females between 40 and 69 yr (average, 56 yr) were cultured and treated with T 3 /T 4 . Results:Studying microdissected, organ-cultured normal human scalp HFs, we show here that T 4 up-regulates the proliferation of hair matrix keratinocytes, whereas their apoptosis is down-regulated by T 3 and T 4 . T 4 also prolongs the duration of the hair growth phase (anagen) in vitro, possibly due to the down-regulation of TGF-␤2, the key anagen-inhibitory growth factor. Because we show here that human HFs transcribe deiodinase genes (D2 and D3), they may be capable of converting T 4 to T 3 . Intrafollicular immunoreactivity for the recognized thyroid hormone-responsive keratins cytokeratin (CK) 6 and CK14 is significantly modulated by T 3 and T 4 (CK6 is enhanced, CK14 down-regulated). Both T 3 and T 4 also significantly stimulate intrafollicular melanin synthesis. Conclusions:Thus, we present the first evidence that human HFs are direct targets of thyroid hormones and demonstrate that T 3 and/or T 4 modulate multiple hair biology parameters, ranging from HF cycling to pigmentation. (J Clin Endocrinol Metab 93: 4381-4388, 2008) C linically, it has long been observed that patients with thyroid dysfunction may show prominent hair abnormalities (1-4) and several in vivo studies have demonstrated (partially conflicting) hair growth-modulatory effects of thyroid hormone (TH) in sheep, rats, and mice (5-8). In humans, hypothyroidism can be associated with telogen effluvium, along with the presentation of dry, brittle, and dull hair shafts (2-4). Confusingly, hyperthyroid states can also lead to effluvium, together with thinned hair shaft diameter and brittle, greasy hair (1, 9 -11), despite an apparently increased hair matrix proliferation (3). Hair shafts of patients with hyperthyroidism also show substantially reduced tensile strength (10). Early graying has been claimed to be related to autoimmune thyroid disease, hypothyroidism, and hyperthyroidism (11, 12), whereas darkening of

Alopecia areata (AA) is a CD8+ T-cell dependent autoimmune disease of the hair follicle (HF) in which the collapse of HF immune privilege (IP) plays a key role. Mast cells (MCs) are crucial immunomodulatory cells implicated in the regulation of T cell-dependent immunity, IP, and hair growth. Therefore, we explored the role of MCs in AA pathogenesis, focusing on MC interactions with CD8+ T-cells in vivo, in both human and mouse skin with AA lesions. Quantitative (immuno-)histomorphometry revealed that the number, degranulation and proliferation of perifollicular MCs are significantly increased in human AA lesions compared to healthy or non-lesional control skin, most prominently in subacute AA. In AA patients, perifollicular MCs showed decreased TGFβ1 and IL-10 but increased tryptase immunoreactivity, suggesting that MCs switch from an immuno-inhibitory to a pro-inflammatory phenotype. This concept was supported by a decreased number of IL-10+ and PD-L1+ MCs, while OX40L+, CD30L+, 4–1BBL+ or ICAM-1+ MCs were increased in AA. Lesional AA-HFs also displayed significantly more peri- and intrafollicular- CD8+ T-cells as well as more physical MC/CD8+ T-cell contacts than healthy or non-lesional human control skin. During the interaction with CD8+ T-cells, AA MCs prominently expressed MHC class I and OX40L, and sometimes 4–1BBL or ICAM-1, suggesting that MC may present autoantigens to CD8+ T-cells and/or co-stimulatory signals. Abnormal MC numbers, activities, and interactions with CD8+ T-cells were also seen in the grafted C3H/HeJ mouse model of AA and in a new humanized mouse model for AA. These phenomenological in vivo data suggest the novel AA pathobiology concept that perifollicular MCs are skewed towards pro-inflammatory activities that facilitate cross-talk with CD8+ T-cells in this disease, thus contributing to triggering HF-IP collapse in AA. If confirmed, MCs and their CD8+ T-cell interactions could become a promising new therapeutic target in the future management of AA.