Bone marrow analysis of immune cells and apoptosis in patients with systemic lupus erythematosus

Abstract

Objectives: To examine the immune cell profile in the bone marrow (BM) of systemic lupus erythematosus (SLE) patients and to assess its clinical relevance. Methods: Sixteen BM samples from 14 SLE patients were compared with seven healthy control samples. The numbers of CD4+ T cells, CD8+ T cells, B cells, plasmacytoid dendritic cells (pDC), macrophages and plasma cells in the BM, and the levels of interleukin-6 (IL-6) expression, were examined by immunohistochemistry. The number of apoptotic cells (active caspase-3+) in the BM was also measured. The association between immune cell subsets and clinical features was also investigated. Results: CD4+ T cells, macrophages and plasma cells were more common in the BM of SLE patients than in healthy controls (1.82±1.45% vs. 0.26±0.12%, p=0.001

16.35±7.17% vs. 8.04±1.38%, p=0.004

and 9.72±5.64% vs. 3.44±0.64%, p<0.001, respectively). Greater numbers of CD4+ T cells and macrophages were associated with high-grade BM damage. The percentage of apoptotic cells in BM specimens from SLE patients was significantly higher than that in controls (2.47±1.35% vs. 0.19±0.22%, p<0.001) and was positively correlated with the number of pDCs (r=0.606, p=0.013). Increased numbers of plasma cells and high IL-6 expression were correlated with anti-double stranded DNA (dsDNA) antibody levels and the SLE disease activity index (r=0.538, p=0.031 and r=0.581, p=0.013, respectively). Conclusion: BM samples from SLE patients showed a distinct immune cell profile and increased numbers of apoptotic cells. This, coupled with a correlation with disease activity, suggest that the BM may play a critical role in the pathogenesis of SLE.