Fibrosis and stem cell epithelial-mesenchymal transition in primary cicatricial alopecias

Scarring Alopecias: Pathology and an Update on Digital Developments

Primary cicatricial alopecias (PCA) represent a challenging group of disorders that result in irreversible hair loss from the destruction and fibrosis of hair follicles. Scalp skin biopsies are considered essential in investigating these conditions. Unfortunately, the recognised complexity of histopathologic interpretation is compounded by inadequate sampling and inappropriate laboratory processing. By sharing our successes in developing the communication pathway between the clinician, laboratory and histopathologist, we hope to mitigate some of the difficulties that can arise in managing these conditions. We provide insight from clinical and pathology practice into how diagnoses are derived and the key histological features observed across the most common PCAs seen in practice. Additionally, we highlight the opportunities that have emerged with advances in digital pathology and how these technologies may be used to develop clinicopathological relationships, improve working practices, enhance remote learning, reduce inefficiencies, optimise diagnostic yield, and harness the potential of artificial intelligence (AI).

Folliculitis Decalvans and Lichen Planopilaris Phenotypic Spectrum-A Series of 7 New Cases With Focus on Histopathology

BACKGROUND

Folliculitis decalvans (FD) and lichen planopilaris (LPP) are classified as neutrophilic and lymphocytic cicatricial alopecias according to the North American Hair Research Society. Recently, a clinical phenotype combining concomitant or sequential features for both was described as a FD LPP phenotypic spectrum (FDLPPPS).

OBJECTIVES

To review the most common phenotypic presentation of FDLPPPS with a main focus on histopathology.

METHODS

We reviewed retrospectively series of 7 patients with a similar phenotypic presentation with special focus on the histologic pattern. All patients presented with concomitant features for FD and LPP and recalcitrant course unresponsive to topical and systemic immunomodulatory/anti-inflammatory agents.

RESULTS

The most common clinical phenotype was that of hairless patches on the vertex with lost follicular ostia and perifollicular scale and the following diagnostic findings: (1) polytrichia; (2) positive bacterial culture for Staphylococcus in over 50% of the samples isolated from pustules and hemorrhagic crusts; (3) "mixed" histologic features for primary cicatricial alopecia including multicompound follicular structures of average 2-5 follicles (follicular packs), atrophy of the follicular epithelium, lymphohistiocytic infiltrate with granulomas, and prominent plasma cells, but absence of neutrophilic infiltrate in all cases except scarce neutrophils in one; and (4) clinical improvement with adjuvant systemic antimicrobials.

CONCLUSIONS

The FDLPPPS may be underreported and should be considered in all cases of LPP recalcitrant to treatment. Dermatologists and dermatopathologists should recognize this phenotypic spectrum to guide optimal clinical management consisting of immunomodulatory and anti-inflammatory agents along with systemic antimicrobials.

Frontal Fibrosing Alopecia. An Example of Disrupted Aryl Hydrocarbon Receptor-Mediated Immunological Homeostasis in the Skin?

Sun protection has been recommended by public health authorities to reduce the risk of keratinocyte and melanocyte tumors, yet some sun exposure is required for vitamin D synthesis. Frontal fibrosing alopecia (FFA) is a cicatricial alopecia that has been reported to have an association with facial photoprotection. The brief review proposes the hypothesis that FFA arises as a result of excessive facial photo-protection with a resultant disturbance in immunological homeostasis mediated via the aryl hydrocarbon receptor-kynurenine pathway axis (AHR/KP) leading to the collapse of immune privilege at the hair bulge.

Profiling the human hair follicle immune system in lichen planopilaris and frontal fibrosing alopecia: can macrophage polarization differentiate these two conditions microscopically?

BACKGROUND

Frontal fibrosing alopecia (FFA) is traditionally regarded as a variant of lichen planopilaris (LPP) based on histological features. Distinct clinical presentation, demographics and epidemiology suggest that differing pathogenic factors determine the final phenotype.

OBJECTIVES

To map the hair follicle immune system in LPP and FFA by systematically comparing key inflammatory markers in defined hair follicle compartments.

METHODS

Lesional scalp biopsies from LPP and FFA and healthy controls were stained with the following immunohistochemical markers: CD1a and CD209, CD4, CD8, CD56, CD68, CD123, CXCR3, forkhead box (FOX)P3, mast cell tryptase and cKit. Macrophage polarization was explored using CD206, CD163, CD86, receptor for advanced glycation end products (RAGE), interleukin (IL)-4 and IL-13 on paired lesional and nonlesional LPP and FFA samples.

RESULTS

Increased numbers of CD8⁺ , CXCR3⁺ and FOXP3⁺ T cells and CD68⁺ macrophages were identified in the distal hair follicle epithelium and perifollicular mesenchyme in both LPP and FFA compared with controls. In both LPP and FFA, total and degranulated mast cells and CD123⁺ plasmacytoid dendritic cells were increased in the perifollicular mesenchyme adjacent to the bulge and infundibulum, whereas numbers of CD1a⁺ and CD209⁺ dendritic cells were significantly reduced in the infundibulum connective tissue sheath. However, only with CD68 staining was a significant difference between LPP and FFA identified, with greater numbers of CD68⁺ cells in LPP samples. Furthermore, the identified macrophage polarization markers downregulated CD86 and upregulated CD163 and IL-4 expression in lesional LPP compared with FFA samples.

CONCLUSIONS

This comparative immunopathological analysis is the first to profile systematically the hair follicle immune system in LPP and FFA. Our analysis highlights a potential role of macrophages in disease pathobiology and suggests that macrophage polarization may differ between LPP and FFA, allowing microscopic differentiation. Linked Comment: Kinoshita-Ise. Br J Dermatol 2020; 183:419-420.

Experimentally Induced Epithelial-Mesenchymal Transition of Human Hair Follicle Stem Cells as a Model of Scarring Alopecia Ex Vivo

Primary cicatricial alopecia is characterized by a permanent "scarring" alopecia. This condition is characterized by the irreversible loss of hair follicles (HF) as a result of apoptosis and epithelial-mesenchymal transition (EMT) of epithelial stem cells localized in the HF bulge.We here report the procedure for experimentally induced EMT in healthy human epidermal stem cells (eSCs) using full-length HF organ culture ex vivo. The present model can be used to recapitulate the complex processes observed in scarring alopecia patient tissues, to further investigate the mechanisms involved in EMT transformation of HFeSCs, and to test substances that could prevent and/or rescue HFeSCs from EMT for the management of scarring alopecias.