In situ immunophenotype of the inflammatory infiltrate in eosinophilic fasciitis.

OBJECTIVE: Eosinophilic fasciitis (EF) is histologically characterized by a fibrous and inflammatory thickening of subcutaneous septal-fascial-perimysial collagenous scaffold. This study aims to define the immunophenotype of inflammatory cells of fascia and muscle underlying the in situ immune response in EF.

METHODS: In 11 cases of EF, we determined the phenotype of inflammatory cells, expression of MHC class I and class II antigens, and C5b9 membranolytic attack complex (MAC) deposits by immunohistochemistry analysis of fascia tissue. Muscle biopsies from 9 patients with active dermatomyositis and 5 with active polymyositis were used as controls. Results. In all patients but one, the inflammatory infiltrate was mainly composed of macrophages associated with CD8+ T lymphocytes (CD4/CD8 ratio < 1) and few eosinophils. Cytotoxic properties were found in 14% of CD8+ T lymphocytes, as shown by granzyme B expression. MHC Class I antigens were overexpressed (5/7) by muscle fibers, with a paratrabecular reinforcement in 4 cases. MHC class II antigens were not expressed by muscle fibers except in one case. C5b9 MAC deposits were not detected.

CONCLUSION: Our in situ characterization of inflammatory infiltrate demonstrates the predominancy of macrophages and CD8+ T lymphocytes. Some of these CD8+ lymphocytes contain granzyme B, thus suggesting a cytotoxic cellular immune response in EF, which could be triggered by infectious or environmental agents.