Abnormal interactions between perifollicular mast cells and CD8+ T-cells may contribute to the pathogenesis of alopecia areata

PLoS One. 2014 May 15;9(5):e94260. doi: 10.1371/journal.pone.0094260. eCollection 2014.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alopecia Areata / blood*
  • Alopecia Areata / immunology*
  • Animals
  • Biopsy
  • CD8-Positive T-Lymphocytes / cytology*
  • CD8-Positive T-Lymphocytes / immunology
  • Cell Proliferation
  • Female
  • Hair Follicle / pathology
  • Humans
  • Inflammation
  • Interleukin-10 / blood
  • Mast Cells / cytology*
  • Mast Cells / immunology
  • Mice
  • Mice, Inbred C3H
  • Middle Aged
  • Phenotype
  • Skin / metabolism
  • Transforming Growth Factor beta1 / metabolism

Substances

  • Transforming Growth Factor beta1
  • Interleukin-10

Grant support

This project was supported in part by a grant from DFG to RP and a PhD fellowship to MB (GRK1727/1) as well as by faculty funds to RP from the University of Manchester and by funds from the Associazione Associazione Nazionale Mediterranea Alopecia Areata funds to RP and MB. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.