Maternal microchimerism in muscle biopsies from children with juvenile dermatomyositis

Objective: Recent advances in molecular techniques have revealed that there is bi-directional transfer of cells between mother and child during pregnancy, and the presence of a mother's cells in her child has been termed maternal microchimerism (MMc). There is the potential for maternal cells to provoke inappropriate immune responses in the child, which could be a factor in autoimmunity including JDM. The aim of this study was to determine whether maternal (female) cells could be detected in frozen muscle sections from seven males (age range 3-13 years) with JDM participating in the Juvenile Dermatomyositis National (UK and Ireland) Cohort Biomarker Study and Repository for Idiopathic Inflammatory Myopathies and sections of muscle controls (age range 2-12 years). Methods: At least 1000 cells from each section underwent FISH and confocal imaging through each nucleus. Concomitant IF for CD45 was used to determine whether MMc in muscle were lymphocytes. A non-parametric Mann-Whitney U-test was used to detect statistical differences. Results: The frequency of MMc was higher in JDM muscle (0.42-1.14%) than in controls (0.08-0.42%) P = 0.01. No CD45 ⁺ MMc were observed. Conclusion: These data confirm an increased frequency of MMc in JDM. More detailed characterization of MMc is required, particularly using phenotypic markers, to explain the role of these cells in JDM.