Genetics of hair texture have implications for therapy
in the lymphocytic inflammatory infiltrate, according to a histopathological study of biopsy specimens.
“Evaluation of the T-cell infiltrate may be a useful way to distinguish CCCA from lichen planopilaris or frontal fibrosing alopecia in some cases when histopathological features alone cannot be used to definitely distinguish between them,” reported Alexandra Flamm, MD, Ata Moshiri, MD, and coauthors from the departments of dermatology and pathology, University of Pennsylvania, Philadelphia.
The histopathological features of CCCA have been characterized previously, but the goal of this study was to go further in piecing together the pathophysiology, they noted.
Horizontal sections of 4-mm punch biopsy specimens were examined from 18 black women with a known diagnosis of CCCA. Both affected and unaffected follicles were evaluated with attention to the number and percentage of CD1a+ Langerhans cells, CD3+, CD4+, and CD8+ lymphocytes.
In this series, the lymphocytic infiltrate in both the affected and unaffected follicles was predominantly composed of CD4+ cells. The perifollicular ratio for CD4+ to CD8+ cells in affected follicles was 5.3:1. It was only modestly lower in unaffected follicles (4.3:1) and in the intrafollicular space of affected follicles (2.5:1).
Affected follicles had a higher number of CD1a+ Langerhans cells than unaffected follicles. This finding suggests, as others have hypothesized, that the antigen-presenting Langerhans cells draw lymphocytes to the follicle, according to the investigators. Elevated numbers of Langerhans cells have also been reported in other forms of scarring alopecia, such as lichen planopilaris (LPP).
In the case of CCCA, CD1a+ Langerhans cells appear to localize to the hair follicle in response to stimulus such as an injury. The CD4+ cells that follow the Langerhans cells participate in an inflammatory reaction that drives follicle destruction. In addition to this damage and scarring, the inflammatory response is also likely to be disrupting the blood supply.
“Fibroplasia associated with follicular scarring displaces blood vessels away from the outer root sheath epithelium,” the authors explained. Ultimately, “the mucinous fibroplasia and perifollicular fibrosis may disrupt and fragment blood vessels in the fibrous sheath, leaving only small clusters of vessels more distant to the keratinocytes in the outer root sheath.”
Prior studies of scarring alopecia diseases, including LLP, frontal fibrosing alopecia (FFA), and keratosis follicularis spinulosa decalvans (KFSD), have typically described a predominantly CD8+ lymphocytic infiltrate. The evidence from this study that the infiltrate is CD4+ predominant in CCCA supports the conclusion that the pathophysiologic features of this type of alopecia are unique, according to the authors.
Work by others has associated CCCA with mutations in the PAD13 gene, which suggests a defect in the formation of hair shaft structure, but this may speak to susceptibility but not the mechanism of hair follicle damage. Rather, this study suggests that it is the concentration of a CD4+ predominant lymphocytic infiltrate in the perifollicular space that induces the pathological events.
For determining the fundamental cause of CCCA, “it will be important to determine what recruits the Langerhans cells to affected follicles,” the investigators suggested. Meanwhile, they expressed hope that the progress being made into decoding the pathogenesis of CCCA will lead to novel therapeutic strategies.
The authors did not list any disclosures. The funding source was listed as the Center for Scientific Review (Grant/Award).
SOURCE: Flamm A et al. J Cutan Pathol. 2020 Feb 18.doi: 10.1111/cup.13666.