Comparison Between Langerhans Cell Concentration in Lichen Planopilaris and Traction Alopecia With Possible Immunologic Implications

Abstract

Lichen planopilaris and long-standing traction alopecia are both traditionally classified as scarring alopecias. The etiology of lichen planopilaris has not been fully elucidated, although an autoimmune mechanism is generally accepted with Langerhans cell involvement implicated in previous studies. The etiology of traction alopecia is generally considered to be the result of mechanical force with subsequent inflammation without an autoimmune component. Langerhans cells in pure traction alopecia have not been previously evaluated nor have Langerhans cell concentrations been compared among the scarring alopecias. We performed double immunostaining with CD1a and CD3 to assess the ratio of Langerhans cells to T lymphocytes in lichen planopilaris and traction alopecia. Sixteen biopsies were evaluated including 9 biopsies of lichen planopilaris and 7 biopsies of traction alopecia. The mean ratio of the concentration of Langerhans cells to T lymphocytes was 1.28 for the lichen planopilaris group and 0.59 for the traction alopecia group. There is a significantly higher ratio of Langerhans cells to T lymphocytes in lichen planopilaris compared with that seen in traction alopecia. This supports previous data recognizing an immune component in lichen planopilaris mediated by Langerhans cells while emphasizing that most traction alopecias are not primarily immune related. Thus, the traditional classification systems for alopecia may need review and revision, especially when looking at etiopathogenesis. However, rare cases of traction alopecia demonstrated ratios similar to those seen in lichen planopilaris. These cases may represent the recently described "traction alopecia" condition, cicatricial marginal alopecia or changes seen in long-standing lesions, emphasizing the need for inclusion of distribution and duration within the clinical information.

Special Stains and Immunohistochemical Stains in Hair Pathology

“…46 This is in accordance with past studies. 47 These data support a role for Langerhans cells in the stimulation of the cytotoxic response to the follicular bulb region.…”

“…44 The ratio of Langerhans cells to T cells has been evaluated in LPP and traction alopecia with the use of CD1a and CD3 immunostains, respectively. 46 Traction alopecia was selected as a control tissue probably because inflammation is not directly involved in its pathogenesis opposed to the primary lymphocytic cicatricial alopecias as LPP. It was found that the mean ratio is significantly higher in LPP (1.28) as compared with traction alopecia (0.59).…”

Regulatory T‐cells in alopecia areata

“…Additionally, studies regarding etiopathogenesis in LPP showed that CD1a-positive Langerhans cells moderate inflammation and may serve as the causative immune cell. 20 There was also a statistically significant decrease in the frequency of T reg in AA vs ISK, which was used as an example of an inflammatory T reg frequency in inflammatory dermatoses, 13 there was also considerable variation in the frequency of T reg among the specimens within the ISK specimens. The frequency seemed to positively correlate with the level of inflammation present, with specimens with mild inflammation having the lowest frequency of T reg and specimens with severe inflammation having the highest frequency of T reg .…”

“…This difference is not unexpected as AA and LPP represent two distinct subtypes of alopecia with different histological findings. Additionally, studies regarding etiopathogenesis in LPP showed that CD1a‐positive Langerhans cells moderate inflammation and may serve as the causative immune cell …”

“…Additionally, pharmacologic augmentation of T reg with low‐dose IL‐2 has been shown to be efficacious in treating AA . Despite this pharmacologic association, a functional link between T reg s and hair follicles was not established until recently, when Ali et al established that T reg in skin plays a major role in hair follicle biology by promoting the function of hair follicle stem cells via the Notch ligand family member, Jagged 1 (Jag1) . Further studies investigating AA, T reg, and their associated receptors and cytokines may have important implications for future interventions.…”