Objectives: The idiopathic inflammatory myopathies (IIM) are a clinically heterogeneous group of conditions affecting the skin, muscle, joint, and lung in various combinations. This study aims to investigate the immunologic heterogeneity through detailed immunophenotyping of peripheral blood mononuclear cells (PBMCs) in IIM patients and healthy controls.
Methods: We collected PBMCs from 17 patients with a clinical diagnosis of inflammatory myositis in the inpatient or outpatient setting and performed immunophenotyping using mass cytometry by time of flight (CyTOF) to simultaneously characterize B, T, and myeloid cell subsets. Data were analyzed using a combination of supervised biaxial gating and unsupervised clustering algorithms including t-distributed stochastic neighbor embedding (tSNE), cluster identification, characterization, and regression (CITRUS), and marker enrichment modeling (MEM).
Results: We identified two distinct immune signatures amongst IIM patients. In one signature, increased CD19+CXCR4hiCCR7hi cells correlated with increased CD3+CXCR4hiCD38hi (r=0.62, p=0.009) and CD14+CD16-CXCR4+CD38+HLADR- (r=0.61, p=0.01) populations. In the second signature, increased CD19+CD21loCD11c+ cells correlated with an increased CD3+CD4+PD1+ (r=0.60, p=0.01) population. Other shared immunologic features amongst IIM patients compared to healthy controls included decreased surface expression of RP105/CD180 on B cells (median mass intensity 39.9 ± 16.0 v. 60.9 ± 20.1, p=0.002). In the T cell compartment, all circulating CD3+CXCR3+ subsets (2.7 ± 2.4 v. 9.6 ± 8.1% of all PBMCs, p=0.0004) were reduced.
Conclusion: Based on circulating B cell phenotype, we identified two distinct immunologic signatures in IIM patients. Future work is needed to determine the significance of these immune signatures for clinical manifestations and treatment responses.
A7.11 Genetic Variation in Promoter Sequence of B-Cell-Activating Factor of the TNF Family (BAFF) in Patients with Idiopathic Inflammatory Myopathies (IIM)
