Understanding autoimmunity of vitiligo and alopecia areata

Abstract

Purpose of review: Vitiligo and alopecia areata are common, disfiguring skin diseases. Treatment options are limited and include nontargeted approaches, such as corticosteroids, topical calcineurin inhibitors, narrow band ultraviolet B phototherapy, and other immune-modifying agents. The purpose of this article is to review shared, novel mechanisms between vitiligo and alopecia areata, as well as discuss how they inform the development of future targeted treatments.

Recent findings: Vitiligo and alopecia areata are both autoimmune diseases, and striking similarities in pathogenesis have been identified at the level of both the innate and adaptive immune system. Increased reactive oxygen species and high cellular stress level have been suggested as the initiating trigger of the innate immune system in both diseases, and genome-wide association studies have implicated risk alleles that influence both innate and adaptive immunity. Most importantly, mechanistic studies in mouse models of vitiligo and alopecia areata have specifically implicated an interferon (IFN)γ-driven immune response, including IFNγ, IFNγ-induced chemokines, and cytotoxic CD8 T cells as the main drivers of disease pathogenesis. These recent discoveries may reveal an effective strategy to develop new treatments, and several proof-of-concept clinical studies support this hypothesis.

Summary: The identification of IFNγ-driven immune signaling pathways has enabled discoveries of potential new treatments for vitiligo and alopecia areata, and supports initiation of larger clinical trials.

Figure 1. Clinical presentations of vitiligo and alopecia areata

A-B) Common vitiligo on the anticubital fossa and extensor knees of a 9-year-old male; C) Segmental vitiligo in a 15-year-old male; D) Alopecia areata on the scalp of a 12-year-old male.

Figure 2. IFN-γ is required for recruitment of CD8+ cytotoxic T cells to sites of inflammation in both vitiligo and alopecia areata

Melanocytes are the target of destructive immune responses in vitiligo, which reside in basal (lower) epidermis. IFN-γ expression recruits a superficial T cell infiltration at the dermal-epidermal junction, which is accessible by topical treatments and narrow band ultraviolet B (nbUVB) phototherapy. The bulk of T cell infiltration in alopecia areata, however, occurs in and around the hair bulb, which is deep within the dermis. Treatment modalities for alopecia areata must therefore be able to effectively penetrate the skin. Systemic treatment could be similarly effective for both diseases. nbUVB, narrowband ultraviolet B; UVA, ultraviolet A.