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AI-07 A new B cell effector pathway with defective negative regulation of TLR7 signaling in human SLE
  1. Scott A Jenks1,
  2. Kevin S Cashman1,
  3. Urko M Marigorta2,
  4. S Sam Lim1,
  5. Michelle Petri3,
  6. Jennifer Anolik4 and
  7. Ignacio Sanz1
  1. 1Department of Medicine, Division of Rheumatology, Lowance Center for Human Immunology, Emory University, Atlanta, Georgia, USA
  2. 2School of Biology and Center for Integrative Genomics, Georgia Institute of Technology, Atlanta, GA, USA
  3. 3Hopkins Lupus Center, Department of Medicine, Johns Hopkins University, Baltimore, MD, USA
  4. 4Department of Medicine, Division of Allergy, Immunology and Rheumatology, University of Rochester Medical Center, Rochester, New York, USA


Background B cell homeostasis is perturbed in SLE patients. in particular, many patients have a large expansion of IgD- CD27- B cells (DN). The DN population is heterogeneous for CXCR5 expression, and CXCR5- DN2 are the majority population in SLE patients but not in HCD (figure 1A). To further understand how these expanded cells differ from other B cells subsets and how they may be dysregulated in SLE, we phenotypically and functionally characterized DN2 in SLE patients and healthy control donors (HCD).

Abstract AI-07 Figure 1

A) representative flow profiles showing that IgD-/CD27-/CXCR5-/CD19++ DN2 B cells are rare in HCD but expanded in many SLE patients. B) the frequency of DN2 for HCD and 2 SLE patient cohorts as percentage of CD19+

Methods B cells subsets were quantified by flow cytometry in HCD and two separate cohorts of lupus patients. Purified DN2 and other B cell subsets were flow sorted and transcriptionally analyzed using RNA sequencing. Toll-like-receptor 7 (TLR7) signaling after stimulation with R848 was measured by staining with anti-phospho-tyrosine specific anti-ERK. Antibody secreting cell differentiation was induced using in vitro stimulation of sorted B cell subsets with a combination of TLR7 and cytokines.

Results DN2 were only a minor B cell subset in HCD (less than 5%) but were elevated in 20% of cohort 1 patients and 60% of cohort 2 (figure 1B). In the patients with the largest expansions almost all B cells (80%) had a DN2 phenotype. DN2 cells predominate in African-American patients with active disease and nephritis, anti-Smith and anti-RNA autoantibodies. Among B cells, they express the highest levels of a T-bet/Zeb2 transcriptional network characteristic of effector T cells and lack the negative TLR regulator, TRAF5. Consistent with this transcriptional profile DN2 are hyper-responsive to TLR7. Moreover, DN2 cells share with activated naïve cells phenotypic, functional features, and a very similar transcriptome. When stimulated in vitro DN2 readily differentiated into plasma cells and produced autoantibodies.

Conclusions DN2 and activated naïve represent a separate B cell lineage with a distinct origin and function as they differed from other B cells subsets both in uniquely expressing several genes and a lack expression of other genes. This study defines a distinct differentiation fate of human autoreactive naïve B cells into effector plasma cell precursors with innate hyper-responsiveness to stimuli relevant to SLE, establishes the components and prominence of extrafollicular B cell activation in this disease, and identifies new therapeutic targets.

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