Immunohistochemical Expression of Immune Regulatory Proteins in Interface Dermatoses

ABSTRACT Cutaneous immune‐related adverse events (irAEs) of immunotherapies, such as anti‐programmed cell death protein‐1 (PD‐1), suggest that immune checkpoint factors may contribute to the pathobiology of lichenoid interface dermatitis in immunotherapy‐naïve patients. Our study aimed to describe innate and adaptive immune markers via immunohistochemical (IHC) staining of lichenoid interface dermatoses. We studied the staining patterns of PD‐L1, STING, IL‐36 gamma, CD8, PD‐1, and LAG‐3 in five interface dermatoses: oral lichen planus (LP) ( n = 10), cutaneous LP ( n = 10), chronic cutaneous lupus erythematosus (CLE) ( n = 11), erythema multiforme (EM) ( n = 11), and toxic epidermal necrolysis (TEN) ( n = 13), by immunohistochemistry (IHC) analysis. Expression was evaluated semi‐quantitively according to the percentage of keratinocytes and dermal lymphocytes stained compared to keratinocytes and resident pericapillary lymphocytes in normal human skin. All interface dermatoses evaluated showed increased expression of PD‐L1 on keratinocytes and LAG‐3 in lymphocytes. STING was increased on the keratinocytes of most specimens. Expression of IL‐36 gamma, in basal layer keratinocytes was more extensive in oral LP and cutaneous LP and varied in CLE, EM, and TEN. Lymphocytic infiltration expressing PD‐1 was elevated in oral LP, cutaneous LP, and CLE. Current thinking is that interface dermatitis is the result of a cell‐mediated immune reaction involving cytotoxic CD8 + T‐cell‐mediated apoptosis of keratinocytes. The findings of this study suggest that in addition to cell‐mediated immunity, innate immune factors may contribute to pathobiology.