Category: Autoimmune rheumatologic diseases
Purpose: Idiopathic Inflammatory Myopathies (IIM) are the most common acquired muscle disorders. In this pilot study, we utilized confocal microscopy using fluorescent antibodies for characterization of dendritic cell (DC) and lymphocyte populations in Dermatomyositis (DM) and Inclusion Body Myositis (IBM) patient biopsies.
Methods: A total of 4 DM and 4 IBM samples were stained for myeloid dendritic cells (mDCs)(BDCA1 and CD11c) and plasmacytoid DCs (pDCs)(BDCA 2 and CD123); or plasma cells (CD138), B-cells (CD20), and T cells (CD4 and CD8), along with cell nuclei (DAPI). Slides were imaged with the SP8 confocal microscope. Regions of Interest were randomly acquired by means of tiling. The resulting data was manually analyzed for number of DCs and lymphocytes by a blinded observer (IBV). Mann-Whitney U test was used for all comparisons.
Results: IBM biopsies had larger proportions of plasma cells (mean of 22 versus 8 per biopsy, p=0.003), CD4+ lymphocytes (73 versus 38, p=0.03), and CD8+ lymphocytes (36 versus vs 10, p=0.002) in comparison with DM. Double-positive staining for mDCs was also greater in IBM (8 versus 1, p<0.001). Moreover, IBM biopsies also had higher numbers of BDCA2+ cells (p=0.008). Double positive pDC and CD20 staining was similar between DM and IBM.
Conclusion: We observed a rich inflammatory milieu in IBM biopsies, with greater amounts of CD8+ and CD4+ T cells as well as mDCs and BDCA2+ cells. Other cell markers considered characteristic of DM, such as the pDC marker CD123, did not differ among the groups<./p>