Résumé :
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Dermatomyositis (DM) is a primary inflammatory myopathy, characterized by perifascicular fiber atrophy, complement-mediated microangiopathy, and B and T helper cell muscle infiltration. Recently, it was shown that muscle-infiltrating CD4+ cells in DM are mainly plasmacytoid dendritic cells (PDC), but not T helper cells. Moreover, a localized polymyositis-like immunopathologic process consisting of MHC-1-expressing fibers attacked by CD8+ T-cells may be occasionally observed in DM. These findings led us to reappraise muscle infiltrating T-cell phenotype in DM by using an innovative flow cytometry (FC) procedure. Ten DM patients and 22 controls with histologically normal muscle were included. Myopathological examination of biopsy samples included routine staining and immunolabelling of MHC-1, C5b-9, CD3, CD4, CD8, CD20, CD68 and CD56/NCAM antigens. Mononucleated cells (MC) were extracted from both muscle (MMC) and peripheral blood (PBMC) and subjected to FC to quantify CD3+, CD3+4+ (T helper), and CD3+8+ (T cytotoxic) cell subsets among leukocytes (CD45+). Calculation of muscle/blood (M/B) ratios for CD45+3+, CD3+4+ and CD3+8+ allowed detecting enrichment/depletion of muscle tissue in helper, cytotoxic, and total T-cells. In controls, CD3 M/B ratio was 0.93±0.22 (mean ± SD), CD4 M/B 0.94±0.31, and CD8 M/B 1.00±0.24. In DM, CD3 M/B was 0.85±0.24 (NS). CD4 M/B ratio was decreased (0.61±0.32; p<0.05), ranging from 0.30 to 1.35. In 8/10 DM patients, CD4 M/B ratio was below 0.8, the lower limit of the 95% confidence interval of controls. In contrast, CD8 M/B ratio was increased (1.94±0.40; p<0.05), ranging from 0.60 to 4.13. In 6/10 DM patients, CD8 M/B ratio was above 1.11, the upper limit of the 95% confidence interval of controls. In conclusion, our findings suggest that CD8+ T-cell-mediated cytotoxicity could occur in DM. Muscle CD4 T-cell depletion was consistent with recent data showing that, in DM, muscle CD4+ cells predominantly are PDC.
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