Interleukin-13 in immunohistochemistry: implications for Grover disease, morphea, and immune checkpoint inhibitor-induced bullous pemphigoid.

Interleukin-13 (IL-13), a key T-helper 2 cytokine, has a central role in type 2 inflammation and is implicated in various skin disorders. This study investigated the IL-13 immunohistochemical expression in skin biopsies from patients with atopic dermatitis (AD), psoriasis vulgaris, morphea, Grover's disease, and immune checkpoint inhibitor-induced bullous pemphigoid (ICI-BP). AD biopsies showed the highest IL-13 expression (mean 27.4%), consistent with its established role in the pathogenesis. Psoriasis displayed moderate positivity (mean 8.62%), indicating IL-13's possible involvement in hybrid or phenotypic overlap forms. Minimal expression was detected in Grover's disease (1.8%) and ICI-BP (2.13%), while no positivity was observed in morphea. These findings highlight the diverse roles of IL-13 across skin disorders, with potential implications for targeted therapies.