The potential role of cytokines and T cells in alopecia areata

T cells play an important role in alopecia areata (AA) because AA can be reinduced by the injection of hair follicle-specific CD8+ T cells into AA scalp biopsies, which were grafted onto scid mice, and the depletion of CD8+ T cells restores hair growth in the Dundee experimental bald rat. Moreover, AA can be transferred by grafting of alopecic skin from C3H/HeJ mice with AA-like hair loss onto unaffected littermates, but the onset of AA is inhibited by i.p. injection of anti-CD44v10 antibodies. Interestingly, grafted anti-CD44v10-treated mice have decreased numbers of CD8+ T cells within the skin. Beside T cells several clinical and experimental data point towards cytokines that might be crucial inducers of hair loss in AA. An aberrant expression of cytokines of the Thl type and IL-1beta has been detected in scalp areas involved by AA, and polymorphisms of cytokine genes such as IL-1-receptor antagonist, IL-1alpha, and TNF-alpha have been shown to determine disease susceptibility and severity. Moreover, IL-1 has been shown to be a potent inhibitor of human hair growth in vitro. Such IL-1-incubated hair follicles show ultrastructural changes similar to those observable in vivo. On the other hand mice transgenic for IL-1alpha develop patchy hair loss and during the depilation-induced hair cycle in C57/BL6 mice, members of the IL-1 family are overexpressed with the onset of spontaneous catagen. Taking all of the presently available data together, we may hypothesize that CD8+ T cells are of crucial importance in AA by their interaction with MHC-I restricted autoantigens, and cytolysis of their target cells. Hair loss, however, may occur because proinflammatory cytokines may interfere with the hair cycle leading to premature arrest of hair cycling.     

Biomarkers of alopecia areata disease activity and response to corticosteroid treatment

Alopecia areata (AA) is a common inflammatory disease targeting the anagen‐stage hair follicle. Different cytokines have been implicated in the disease profile, but their pathogenic role is not yet fully determined. We studied biopsies of pretreatment lesional and non‐lesional (NL) scalp and post‐treatment (intra‐lesional steroid injection) lesional scalp of 6 patchy patients with AA using immunohistochemistry and gene expression analysis. Immunohistochemistry showed increases in CD3⁺, CD8⁺ T cells, CD11c⁺ dendritic cells and CD1a⁺ Langerhans cells within and around hair follicles of pretreatment lesional scalp, which decreased upon treatment. qRT‐PCR showed in pretreatment lesional scalp (compared to NL) significant increases (P < 0.05) in expression of inflammatory markers (IL‐2, IL‐2RA, JAK3, IL‐15), Th1 (CXCL10 and CXCL9), Th2 (IL‐13, CCL17 and CCL18), IL‐12/IL‐23p40 and IL‐32. Among these, we observed significant downregulation with treatment in IL‐12/IL‐23p40, CCL18 and IL‐32. We also observed significant downregulation of several hair keratins in lesional scalp, with significant upregulation of KRT35, KRT75 and KRT86 in post‐treatment lesional scalp. This study shows concurrent activation of Th1 and Th2 immune axes as well as IL‐23 and IL‐32 cytokine pathways in lesional AA scalp and defined a series of response biomarkers to corticosteroid injection. Clinical trials with selective antagonists coupled with cytokine‐pathway biomarkers will be necessary to further dissect pathogenic immunity.     

Substance P as an immunomodulatory neuropeptide in a mouse model for autoimmune hair loss (alopecia areata)

Alopecia areata (AA) is an autoimmune disorder of the hair follicle characterized by inflammatory cell infiltrates around actively growing (anagen) hair follicles. Substance P (SP) plays a critical role in the cutaneous neuroimmune network and influences immune cell functions through the neurokinin-1 receptor (NK-1R). To better understand the role of SP as an immunomodulatory neuropeptide in AA, we studied its expression and effects on immune cells in a C3H/HeJ mouse model for AA. During early stages of AA development, the number of SP-immunoreactive nerve fibers in skin is increased, compared to non-affected mice. However, during advanced stages of AA, the number of SP-immunoreactive nerves and SP protein levels in skin are decreased, whereas the expression of the SP-degrading enzyme neutral endopeptidase (NEP) is increased, compared to control skin. In AA, NK-1R is expressed on CD8+ lymphocytes and macrophages accumulating around affected hair follicles. Additional SP supply to the skin of AA-affected mice leads to a significant increase of mast cell degranulation and to accelerated hair follicle regression (catagen), accompanied by an increase of CD8+ cells-expressing granzyme B. These data suggest that SP, NEP, and NK-1R serve as important regulators in the molecular signaling network modulating inflammatory response in autoimmune hair loss.     

Induction of cellular immunity against hair follicle melanocyte causes alopecia

Alopecia areata (AA) is generally regarded as an organ-specific autoimmune disease. Although it has been hypothesized that the autoimmunity is mediated by T cells and that hair follicle melanocyte is one of the targets, definitive evidence is lacking. We here demonstrate that AA-like lesions can be induced in mice by inducing CD8⁺ T-cell-mediated immunity to hair follicle melanocytes. We found that hair loss was induced in mice-bearing interleukin-12-producing B16 melanoma cells by the depletion of CD4⁺ T cells, accompanied by vitiligo-like coat color change. The alopecic lesions varied in size from pachy to extensive. In many instances, hair loss developed and was followed by the regrowth of white hairs. Histological analysis revealed that mononuclear cells infiltrated in and around the bulb region of hair follicles. Furthermore, immunohistochemical examination clearly showed the intra-follicular infiltration of CD8⁺ T cells. Neither the vitiligo-like coat color nor AA-like lesions were induced when CD8⁺ T cells were codepleted. These observations indicate that the induction of CD8⁺ T-cell-mediated immunity against hair follicle melanocytes causes alopecia. It is thought that there are many types of AA with different mechanisms, targets etc. Although hair follicle melanocytes have long been thought to be one of the targets of AA, evidence to support the hypothesis is sparse. Therefore, we believe that our observation is significant to support the hypothesis.     

CD8+ mycosis fungoides clinically masquerading as alopecia areata

A 33‐year‐old female with a 7‐year history of CD8‐positive hypopigmented mycosis fungoides (MF) involving the trunk and extremities presented with a large well‐defined alopecic patch on her frontal scalp. Clinically, this area resembled alopecia areata (AA) and was without hypopigmentation or erythema. A scalp biopsy revealed a non‐scarring inflammatory alopecia and a superficial band‐like atypical lymphoid infiltrate with prominent epidermotropism. Atypical, predominately CD8‐positive lymphocytes were seen surrounding and infiltrating the bulb portion of several hair follicles. Treatments for her MF lesions have included topical bexarotene, topical corticosteroids and phototherapy. Her alopecia has been treated with high potency topical corticosteroids and multiple intralesional triamcinolone injections with very minimal hair regrowth to date. Alopecia due to cutaneous lymphoma is an uncommon phenomenon but can occur in erythrodermic MF or Sezary syndrome. AA‐like changes have most often been reported in conventional patch/plaque stage MF and folliculotropic MF. In these cases, the atypical lymphoid infiltrate is comprised predominately of CD4‐positive lymphocytes. This is a rare report of a CD8‐positive MF causing AA‐like changes. This case highlights the importance of a scalp biopsy in patients with a history of cutaneous lymphoma presenting with alopecia in order to evaluate the nature of their hair loss.     

A graft model for hair development

Abstract:  Follicular cell implantation (FCI) is an experimental cell therapy for the treatment of hair loss that uses cultured hair follicle cells to induce new hair formation. This treatment is based on the demonstration that adult dermal papilla cells (DPC) retain the hair inductive capacity they acquired during hair morphogenesis in the embryo. For FCI, hair inductive cells are isolated from scalp biopsies and then propagated in culture in order to provide enough cells to generate many new follicles from a few donor follicles. Following expansion in culture, the cells are implanted into the scalp where they induce the formation of new follicles. Because the process relies on the ability to retain the potential for hair induction during the expansion of DPC in culture, we sought a consistent, reliable and easily performed in vivo assay in which to test hair induction. In this study, we describe a simple graft model that supports hair morphogenesis. The assay combines dermal cells with embryonic mouse epidermis that provides the keratinocyte component of induced follicles. The grafts are placed under a protective skin flap in the host athymic mouse where the cells will form a skin graft with hair if the dermal cells are hair inductive DPC. Using the assay, freshly isolated and cultured mouse embryo dermal cells as well as cultured dermal papilla cells from other species all induced hair formation. The induced hairs were aesthetically indistinguishable from those of the epidermal donor in length, thickness, and pigmentation, and they were histologically normal.     

Characterization of infiltrating T cells in human scalp explants from alopecia areata to SCID nude mice: possible role of the disappearance of CD8+ T lymphocytes in the process of hair regrowth

T cells may play a role in the pathogenesis of alopecia areata (AA). We attempted to elucidate the linkage between infiltrating T cells and hair regrowth processes by grafting scalp skin from the affected region of patients with AA onto severe combined immune deficiency (SCID) nude mice. When the AA scalp was grafted into the mice, the grafts were accepted, and normal hair regrowth was observed. Before grafting, CD4+ and CD8+ T cells had infiltrated into the peribulb area. After grafting, the telogen hair shifted to anagen hair, and the CD4+ and CD8+ T cell infiltrates in the bulb area decreased in all cases. CD8+ T cells had almost disappeared from all portions of the follicles. It has been suggested that CD8+ T cells play a crucial role in the pathogenesis of AA. The absence of CD8+ T lymphocytes that responded to follicular autoantigens may induce hair regrowth in the grafted skin. In addition, the CD4+ human T cells that had infiltrated or still remained in the upper-middle portions including the bulge area accompanied the HLA-DR expression after grafting. Infiltrating or surviving T cell phenotypes and locations changed during the hair cycle in the grafts. These results indicate that the location of infiltrated T cells and their phenotypes may participate not only in hair loss but also in regrowth of hair in AA.     

毛囊干细胞在盘状红斑狼疮性脱发和斑秃中的变化及意义

目的了解毛囊干细胞在常见瘢痕性脱发和非瘢痕性脱发中的变化及意义。方法采用SP免疫组化法检测毛囊干细胞常用标志分子CK15、CD200在常见瘢痕性脱发和非瘢痕性脱发即盘状红斑狼疮(DLE)和斑秃皮损中的表达。每组8例患者,以同等数量正常人头皮做对照。结果毛囊干细胞标志CK15、CD200在正常对照的阳性率均为100%,而在DLE患者头皮中的阳性率分别为37.5%和12.5%,同正常对照相比均明显减少(P<0.05);斑秃患者毛囊中CK15阳性表达率为100%,CD200阳性表达率为50%,CD200阳性表达率与正常对照相比明显减少(P<0.05)。结论毛囊干细胞在DLE患者中明显受损,可能与其永久性脱发有关;而在斑秃中毛囊干细胞无减少。CD200在毛囊表达减少可能与斑秃及DLE的发病相关。     

Differences in hair follicle dermal papilla volume are due to extracellular matrix volume and cell number: implications for the control of hair follicle size and androgen responses

The size of a hair follicle is thought to be determined by the volume of its dermal papilla. The volume of the dermal papilla depends on the number of cells it contains and on the volume of the extracellular matrix. To establish which of these two variables is related to differences in hair follicle size we performed a stereologic study on 235 hair follicles from different sites, including male facial skin (beard), female facial skin, and scalp. In facial follicles there was a strong correlation between the area of the hair cortex and the volume of the dermal papilla. The area of the hair cortex also correlated with the number of cells in the dermal papilla and with the volume of dermal papilla per cell. In scalp hair follicles, where there was a smaller range of sizes, the correlations between these variables were weaker. In large male facial follicles the mean total dermal papilla volume was almost 40-fold higher than in vellus follicles from female facial skin. This difference was associated with a mean 17-fold greater number of cells in the dermal papilla and a 2.4-fold greater volume associated with each cell. Intermediate results were obtained in scalp follicles. In many regions of the skin hair follicles enlarge in response to androgens during adult life hair. Our results imply that the increase in the volume of the dermal papilla in these follicles is due to an increase in the number of cells, either through proliferation or through the migration of cells from the follicular dermal sheath, and to an increase in the amount of extracellular matrix per cell. As androgens are thought to act primarily on the dermal papilla, these changes may have a direct bearing on the mechanism of androgen-mediated alterations in hair follicle size.     

Normalisation of hair follicle morphology in C3H/HeJ alopecia areata mice after treatment with squaric acid dibutylester

Alopecia areata is a non-scarring, reversible disorder, presumably caused by an autoimmune attack on anagen hair follicles. Treatments are numerous, and most of these are ineffective. However, the elicitation of contact dermatitis on the affected skin is commonly associated with hair regrowth. A major advance in the study of alopecia areata has been the introduction and characterisation of the C3H/HeJ mouse model that exhibits many features of the human disease. In this study we examined the effects of squaric acid dibutylester treatment on hair follicles and the associated leukocyte infiltrate in alopecia areata mice by light and transmission electron microscopic analysis. This was compared with unaffected normal mice and alopecic untreated mice. Experimental mice were treated unilaterally with the contact allergen squaric acid dibutylester and the skin was assessed after hair regrowth. The characteristic pathological picture of alopecia areata was observed in alopecic but not normal mice. Nine of eleven experimental mice regrew hair on the treated side only and this was associated with a reduction in peri/intrafollicular inflammatory cell infiltrates, hair follicle dystrophy, melanin incontinence/clumping, and an increase in the numbers of hair follicles in full anagen. This normalisation of hair follicle status after treatment reflects the successful reversal of disease in these mice. The mechanism of action of topical immunotherapy with a potent contact allergen such as squaric acid dibutylester still needs to be elucidated, but an altered immune milieu is suspected. This study further validates the C3H/HeJ mouse model of alopecia areata in the search for therapeutic interventions in this common hair follicle disorder.     

Alopecia as a rare but distinct manifestation of pemphigus vulgaris

Background Pemphigus vulgaris (PV) patients may develop scalp erosions, however, the development of alopecia has been reported to be extremely rare. Objective To delineate the clinicopathological features of alopecia in PV and provide insight into the pathogenesis of this rarely observed manifestation. Methods A retrospective case note review was performed on five PV patients presenting with progressive hair loss and alopecic patches. Data were collected on demographics and clinical findings. Results for hair pull tests, direct immunofluorescence study of plucked hairs, established laboratory tests to detect anti‐desmoglein 1 and 3 autoantibodies and scalp swab culture were recorded. A combination of vertical and horizontal sectioning technique enabled detailed histopathological analysis of alopecic patches. Clinical course was monitored. Results Anagen hair follicles with the outer root sheath structure were easily pulled from perilesional scalp, with intercellular IgG deposition on the outer root sheath keratinocytes. Acantholysis between outer root sheath keratinocytes extending from the infundibulum to suprabalbar level was evident in anagen hair follicles of affected lesions. Perifollicular cell infiltration was observed in the lesions where scalp swabs detected micro‐organisms. The bulge stem cell area was mostly intact. Alopecia was non‐scarring and following 4 weeks of therapy hair re‐growth was seen in all patients. Conclusion In PV, the combination of anti‐desmoglein autoantibody‐mediated acantholysis in conjunction with secondary factors, such as inflammatory changes due to infection, may cause weakening of hair follicle anchorage resulting in hair loss and alopecic patches. This unusual clinical phenotype should alert physicians to PV as a potential diagnosis.     

Type 1 interferon signature in the scalp lesions of alopecia areata

Background Autoimmune attack of the bulbar region of anagen phase hair follicles by CD8+ T cells and Th1 cytokines has been proposed to result in hair loss in alopecia areata (AA). The initiating stimuli are unknown. As interferon‐α therapy may trigger AA, we propose that type 1 interferons are involved in the induction of disease. Objectives To compare lesional scalp from patients with AA with scalp lesions of cutaneous diseases associated with local type 1 interferon‐related protein expression. Methods Lesional scalp of patients with AA, discoid lupus erythematosus, lichen planopilaris and androgenetic alopecia was examined by immunohistochemistry for expression of the type 1 interferon‐inducible myxovirus protein A (MxA), the chemokine receptor CXCR3, and the cytotoxic proteins granzyme B (GrB) and T‐cell intracytoplasmic antigen 1 (TiA‐1). Results MxA was expressed in the intradermal and subcutaneous compartments of the hair follicle including sebaceous glands in inflammatory AA similar to lesions of cicatricial alopecia (discoid lupus erythematosus, lichen planopilaris) but not in the epidermal compartment of AA, and not at all in noninflammatory AA or androgenetic alopecia. The location of CXCR3‐expressing cells correlated with MxA expression. The inflammatory cells around the hair follicle in AA included a lower number of GrB+ and TiA‐1+ cells compared with cicatricial alopecia and demonstrated predominant TiA‐1+ expression. Conclusions We demonstrate the expression of type 1 interferon‐related proteins in the inflammatory lesions of AA. The distribution pattern of the interferon signature and cytotoxicity‐associated proteins in AA differs from cicatricial alopecia.     

Expression of hair follicle stem cells detected by cytokeratin 15 stain: implications for pathogenesis of the scarring process in cutaneous lupus erythematosus

Background Discoid lupus erythematosus (DLE) is a scarring disease. Although the scarring and deformity may affect any part of the body, such changes have been reported to be most obvious on the face and scalp. The pathogenesis behind this scarring process is not well understood. Once lesions have scarred, recurrent disease tends to occur at the edge of the scarred lesions but not within them. Objectives The fact that inflammation in DLE generally involves the bulge area of the follicles raises the possibility that damage to the stem cells of the bulge region may be one process leading to the permanent loss of follicles. The aim of this study was to investigate the role of the hair follicle stem cells which reside in the bulge region in the scarring process in cutaneous lupus erythematosus (CLE). Methods We studied the reactivity of an antibody to the CD8 antigen (C8/144B), which recognizes cytokeratin (CK) 15 and preferentially immunostains hair follicle stem cells without staining the remaining hair follicle, on skin biopsies (scalp and body lesions) from patients with CLE (36 with discoid lesions and 10 with subacute lesions). Normal scalp and body biopsy specimens served as controls. The correlation between the extent of the cytotoxic inflammatory cell infiltrate (CD8+) and the presence of stem cells was investigated. Results were analysed semiquantitatively. Results The expression of CK15 in hair follicle stem cells was variable in the DLE lesions; there was normal to moderate CK15 expression at the bulge region of hair follicles when surrounded by mild or moderate inflammatory infiltrate (CD8+), but in cases of severe inflammation, CK15 expression was weak or absent. Conclusions The bulge region appears to be involved in this disease as part of a broader involvement of the hair follicles; it is secondarily affected by the surrounding inflammatory cell infiltrate. Expression of C8/144B diminished and was then absent, indicating either damage to stem cells or differentiation to help in the repair process. Damage to follicular stem cells may help to explain the irreversible alopecia and the scarring process which characterize this disease.     

An unexpected twist in alopecia areata pathogenesis: are NK cells protective and CD49b+ T cells pathogenic?

Please cite this paper as: An unexpected twist in alopecia areata pathogenesis: are NK cells protective and CD49b+ T cells pathogenic? Experimental Dermatology 2010; 19 : e347–e349. Abstract: Natural killer (NK) cells have become a recent focus of interest in alopecia areata (AA) research. To further investigate their role in an established mouse model of AA, lesional skin from older C3H/HeJ mice with AA was grafted to young C3H/HeJ female mice, and NK cells were depleted by continuous administration of rabbit anti‐asialo GM1. As expected, this significantly reduced the number of pure NK cells in murine skin, as assessed by NKp46 quantitative immunohistochemistry. Quite unexpectedly, however, the onset of hair loss in C3H/HeJ mice was accelerated, rather than retarded. NK cell depletion was accompanied by a significant increase in the number of perifollicular CD49b+T cells in the alopecic skin of anti‐asialo GM1‐treated mice. These findings underscore the need to carefully distinguish in future AA research between pure NK cells and defined subsets of CD49b+ lymphocytes, as they may exert diametrically opposed functions in hair follicle immunology and immunopathology.     

The Ludwig pattern of androgenetic alopecia is due to a hierarchy of androgen sensitivity within follicular units that leads to selective miniaturization and a reduction in the number of terminal hairs per follicular unit

Background Hair follicles exist within follicular units (FUs). In utero the central primary hair follicles are surrounded by smaller secondary follicles. Each FU is nourished by a single arborizing arrector pili muscle that attaches circumferentially around the primary follicle with variable attachment to other follicles. Androgenetic alopecia (AA) miniaturizes susceptible scalp hair follicles in a distinctive and reproducible fashion manifesting in different patterns between men and women. Objectives We hypothesized that there is an additional layer to the patterning in AA, with a hierarchy of susceptibility within FUs to AA, and that the diffuse hair loss seen in women with AA is due to a reduction in the number of terminal hairs per FU rather than uniform miniaturization of entire FUs. Methods We compared the mean numbers of FUs and terminal hairs per FU in 4‐mm scalp punch biopsies in 24 women with AA with those in 21 controls. Results There was no significant difference in the number of FUs; however, women with AA had 2·40 terminal hairs per FU compared with 3·38 in the control group (P = 0·0001) associated with a mean increase of 0·6 vellus hairs per FU. Complete miniaturization of all hairs within the FU was not seen. Conclusions Diffuse hair loss in women with AA is due to a reduction in the number of terminal hairs per FU and an increase in the number of vellus hairs. This supports the hypothesis of a hierarchy of susceptibility within FUs to AA. Further investigation is required to ascertain whether secondary and tertiary hair follicles are more susceptible than primary follicles.     

CD200在斑秃患者淋巴细胞和毛囊上的表达和意义

目的 探讨CD200在斑秃患者外周血淋巴细胞和头皮毛囊上的表达。方法 用流式细胞仪检测CD200在43例斑秃患者外周血淋巴细胞上的表达。免疫组化法检测CD200和正常毛囊外根鞘基底层标记CK15（cytokeratin 15）在8例斑秃患者毛囊上的表达,以同等例数健康人的标本做对照,进行分析比较。 结果 CD200在斑秃患者外周血总淋巴细胞上及T淋巴细胞上的表达率分别为5.73% ± 3.46%,8.85% ± 4.8%,明显低于健康对照人群（12.01% ± 4.9%;12.31% ± 3.12%,t值分别为6.865,3.964,P值均 ＜ 0.05;而在患者B淋巴细胞上的表达比例为74.68 ± 8.12,较健康对照人群差异无统计学意义（75.750 ± 9.447, t = 0.570,P > 0.05）;斑秃患者毛囊上CD200的表达较健康对照人群亦明显下降（P ＜ 0.05）,而CK15较健康对照无明显下降。结论 CD200在斑秃患者外周血淋巴细胞和毛囊上表达的下降可能参与了斑秃的发病。     

Expression of vascular endothelial growth factor (VEGF) in various compartments of the human hair follicle

Abstract Hair follicle vascularization appears to be closely related to the processes involved in hair cycle regulation, in which growth factors, cytokines and other bioactive molecules are involved. In particular, vascular endothelial growth factor (VEGF), essential for angiogenesis and vascular permeability, may be responsible for maintaining proper vasculature around the hair follicle during the anagen growth phase. The aim of our study was to compare the in vitro angiogenic capacity, i.e. the steady-state expression of the VEGF gene, of different cultured cell types derived from normal human hair follicles, corresponding to different follicular compartments. Human dermal papilla cells (DPC), fibrous sheath fibroblasts, dermal fibroblasts, and follicular and interfollicular keratinocytes were cultured and studied in vitro for VEGF expression at the mRNA level using RT-PCR, and for VEGF protein synthesis by radioimmunoprecipitation and immunocytochemistry. In vivo examination for VEGF expression in human terminal hair follicles was performed using immunohistochemical methods. In the present report the expression of four different VEGF molecular isoforms, differing in their angiogenic capacity, are described in different cultured follicular cell types for the first time. Cultured follicular cells strongly expressed mRNA of four VEGF molecular species identified as the 121-, 145-, 165- and 189-amino acid splice variants, the most prominent being the 121-amino acid molecule. DPC, and also other mesenchymal cells such as fibrous sheath fibroblasts and dermal fibroblasts, in vivo and in vitro strongly expressed VEGF mRNA and synthesized a 46-kDa VEGF protein, whereas follicular and interfollicular keratinocytes in vitro expressed lower levels of VEGF mRNA and proteins than mesenchymal cells. As the highest expression of VEGF was found in DPC, we suggest that DPC are mainly responsible for angiogenic processes possibly related to the human hair cycle. Received: 14 January 1998 / Received after revision: 16 July 1998 / Accepted: 30 July 1998     

Expression of Ras homologous B protein in the human scalp skin and hair follicles: hair follicle cycle stages‐associated changes

Background: RhoB belongs to the Ras homologous (Rho) subfamily which consists of low molecular weight mass GTP‐binding proteins. Rho proteins are regulatory molecules that mediate changes in cell shape, contractility, motility and gene expression. Aim: To test the hypothesis that ‘RhoB protein is expressed in the human skin and its expression undergoes hair follicle cycle dependent changes'. To test this hypothesis, we examined the expression of RhoB in the normal human skin and hair follicles (HFs) using immunohistochemical methods. Methods: A total of 50 normal human scalp skin specimens were obtained from 50 females (age: 53–57 years) undergoing elective cosmetic plastic surgery. The specimens were obtained from both frontal and temporal regions of the scalp. A total of 50 HF, (35 anagen, 10 catagen and 5 telogen) were examined in each case using immunohistologic staining methods. Semiquantitative analysis was done. Results: RhoB protein was strongly expressed in the various elements of the human scalp skin and hair follicles. In the epidermis, a moderate RhoB immunoreactivity was found in all layers except stratum corneum where RhoB protein was completely absent. In sebaceous glands, a strong RhoB immunoreactivity was detected in all sebaceocytes. In the hair follicles, the expression of RhoB protein showed hair follicle cycle stages‐associated changes, i.e. strong expression during anagen, but weak and completely absent expressions during catagen and telogen phases, respectively. Semiquantitative analysis revealed statistically significant high expression values (staining intensity, percentage of positive cells and immunoreactivity scores) in the anagen VI hair follicles compared to either cantagen or telogen ones (p < 0.05). Similarly, RhoB protein expression was significantly high in the stratum basale, stratum spinosum and sebaceous glands compared to stratum granulosum (p < 0.05). Conclusions: Here we report, for the first time, the distribution of RhoB protein in the human scalp skin and hair follicles. We also provide the first indication that there are variations in the expression of this protein in the different stages of the hair cycle. Adly M.A, Assaf H.A, Hussein M.R.A. Expression of Ras homologous B protein in the human scalp skin and hair follicles: hair follicle cycle stages‐associated changes