Background/Purpose: SLE is an autoimmune disease, which exhibits multiple B cell abnormalities including expanded populations of plasmablasts and DN memory cells as well as a contracted unswitched memory subset.  The transcriptional profiles that underlie these homeostatic changes are poorly understood. To remedy this knowledge gap and generate insight into the disease pathogenesis, we carried out transcriptome analysis of sorted B cell subsets. 

Methods: B cell subsets were flow sorted from 12 healthy controls (HC) and 13 SLE patients with low disease activity (SLEDAI<6):  naïve (IgD⁺CD27^–), unswitched memory (IgD⁺CD27⁺), switched memory (IgD^–CD27⁺), DN memory (IgD^–CD27^–) and plasmablasts (IgD^–CD27⁺⁺CD38⁺⁺).  Total RNA was hybridized to Human Genome U133 Plus 2.0 GeneChip (Affymetrix).  The scans were subjected to quality control measures and the resulting CEL files normalized with Robust Multi-array Average (RMA).  All calculations and analyses were carried out using R/Bioconductor computational tools.  To identify differentially expressed genes (DEGs) between groups of samples, a two-way ANOVA model using Method of Moments was applied.  Gene that exhibited a FDR <0.05 and fold change >2 or <-2 were considered significantly different.

Results: Overall, there are fewer DEGs among the three memory B cell subsets than between naïve and each of the three memory subsets in both healthy subjects and SLE patients, suggesting that the gene expression program is quite similar among all the memory B cells in HC and SLE.  IL4R and IL21R are upregulated in naïve cells whereas IL6R is over-expressed in memory cells.  Also upregulated in naïve cells is TCL1A, which promotes Akt-mediated survival.  TACI is upregulated in the switched and unswitched memory subsets compared to naïve cells in HC and SLE, and is higher in SLE DN B cells compared to the same population in HC.  SLE DN cells had also higher levels of AICDA and FcRL4.  Overall, most DEGs differentials between the two cohorts were identified in the DN subset.  Within either cohort, thousands of DEGs were observed between plasmablasts and the other four B cell subsets.

Conclusion: The transcriptome of multiple B cell subsets was remarkably similar between HC and SLE patients with low disease activity suggesting that most differences in active disease may be due to extrinsic differences.  Our results are consistent with the important role of IL-4 and IL-21 as growth factors for naïve cells and the known activity of IL-6 in memory differentiation into plasma cells. Of great interest is the upregulation of TACI, AICDA and FcRL4 in DN B cells, a population expanded in SLE.  The implications for the potential germinal center origin and activation status of these cells, reported to represent exhausted cells in HIV infection, will be discussed.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/gene-expression-profiling-analysis-of-human-b-cell-subsets-in-health-and-systemic-lupus-erythematosus/