Increased matriptase activation in inflamed intradermal nevus, prurigo nodularis, and natural killer cell lymphoma with skin metastasis. Tissue sections of frozen human skin specimens from 3 skin disorders, including intradermal nevus (A and B), prurigo nodularis (C and D), and natural killer cell lymphoma with skin metastasis (E and F), were analyzed by immunohistochemistry for morphology by H & E staining (A, C, E) and for activated matriptase (B, D, F). Bars = 50 μm.