0912: CD11c⁺CD21⁻ Autoimmune-Associated B Cells Derived from Double-Negative IgD⁻CD27⁻ Subsets Exhibit Enhanced IFNLR1 Expression in Systemic Lupus Erythematosus

Background/Purpose: Autoimmune-associated B cells (ABCs) are increasingly recognized for their role in the pathogenesis of systemic lupus erythematosus (SLE), yet their developmental origins and specific functions remain unclear. Interferon-lambda (IFN-λ), a type III interferon implicated in SLE, may have distinct effects from the well-established pathogenic role of interferon-alpha (IFN-α), still its contribution remains incompletely understood. Prior studies suggest that ABCs—characterized by a CD11c⁺CD21⁻ phenotype—are most prevalent within the double-negative (DN) B-cell subset, which also shows heightened responsiveness to IFN-λ. We hypothesize that CD11c⁺CD21⁻ ABCs, predominantly arising from the DN IgD⁻CD27⁻ B-cell subset, exhibit enhanced responsiveness to IFN-λ, contributing to their pathogenic role SLE through upregulated IFNLR1 expression.

Methods: To investigate the development and function of ABCs, peripheral blood mononuclear cells (PBMCs) were isolated from patients with SLE (n = 18). Flow cytometry was employed to quantify CD11c⁺CD21⁻ ABCs across four B-cell subsets: naïve, switched memory (SM), unswitched memory (USM), and DN. IFNLR1 expression was later assessed within these subsets (n = 3).

To explore the intrinsic differentiation potential of ABCs, in vitro stimulation assays were performed using sorted-purified naïve, SM, USM, and DN B cells from healthy donors (HDs) (n = 3). Cells were cultured under ABC-inducing conditions, including B-cell receptor stimulation, R848 (TLR7/8 agonist), IFN-γ, IL-21, and BAFF. Following culture, the induction of CD11c⁺CD21⁻ ABCs and IFNLR1 expression were analyzed by flow cytometry.

Results: Flow cytometric analysis of PBMCs from SLE patients (n = 18) revealed that CD11c⁺CD21⁻ ABCs were most enriched within DN B-cell subset. Their frequency was significantly higher relative to total CD19⁺ B cells compared to other subsets. The mean frequencies of ABCs were 6.46% in DN, 2.59% in USM, 1.37% in naïve, and 0.29% in SM B cells (p < 0.02).

In vitro differentiation assays using sorted B-cell subsets from HDs (n = 3) demonstrated that DN and SM B cells exhibited the highest propensity to differentiate into ABCs under stimulatory conditions. The mean frequencies of induced ABCs were 46.2% for DN, 32.4% for SM, 13.4 for naïve and 4.3 for USM B cells.

Assessment of IFNLR1 expression showed significantly elevated levels on CD11c⁺CD21⁻ ABCs within the DN subset in SLE patients (p < 0.02). In vitro, ABCs derived from DN B cells exhibited a 6.3-fold increase in IFNLR1 expression under ABC-inducing conditions, compared to 2.5-fold, 1.6-fold, and 1.6-fold increases in ABCs derived from SM, naïve, and USM B cells, respectively.

Conclusion: These findings identify the DN B-cell subset as a key origin of CD11c⁺CD21⁻ autoimmune-associated B cells in SLE and highlight their enhanced capacity for IFNLR1 expression. The preferential differentiation of DN B cells into ABCs, coupled with their heightened responsiveness to IFN-λ, driven by increased IFNLR1 expression, suggests a distinct IFN-λ–mediated pathway in B-cell–driven autoimmunity. This IFN-λ–IFNLR1 axis may represent a novel therapeutic target for modulating B-cell–driven autoimmunity in SLE.