Immunohistochemical evaluation of apocrine and eccrine involvement in HS has been performed retrospectively on sections of HS from vulval skin. Markers of apocrine differentiation (GCDFP-15, CD15, lysozyme) and eccrine differentiation (GCDFP-15, S-100, CA-19.9, HMB45) were used.
In total 13 cases were examined; the majority of glands identified in the samples from vulval skin were eccrine. Apocrine glands were either not seen or were present away from the area of active inflammation in 10 of the 13 cases. In 2 cases the inflammatory process had apparently destroyed all glands. Follicular obstruction was evident in 11 of the 13 cases. The inflammatory component varied, being severe in some cases to minimal in burnt-out disease. When present, inflammation of glands was only evident in association with poral occlusion, suggesting this was a secondary phenomenon. Fibrosis appeared to correlate with more chronic disease .
In a study looking at acute lesions of HS, im-munohistochemical examination showed a pattern of lymphocytic predominance suggestive of a cell-mediated response characterized by CD4 helper cells (Fig. 4.5) expressing HLA-DR positivity in keeping with an activated state (personal communication, Dr Julian Barth). The T-helper-to-suppressor ratio was high in the acute HS lesions and in keeping with a cellmediated response.
These changes mirror those found in experimentally induced early acne lesions  where a high ratio of T4 to T8 cells was found at 24 h. Further work looking at time-coursed biopsy samples in acne also confirmed these findings .
These identical results in early HS and acne lesions suggest there may be a common mechanism with a type-IV delayed hypersensitivity response to an as yet unidentified antigen.
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