Background/Purpose: Age-associated B cells (ABC), defined as CD11c+ T-bet+ or CD11c+CD21-, represent a subset of B lymphocytes that are increased in systemic lupus erythematosus (SLE) patients. ABC are posited to differentiate into autoreactive plasma cells in autoimmune disease. We and others reported that this population is found within the naïve and memory B cell compartments, but are most expanded in the IgD- CD27- CD24- CD21- (DN2) B cell subset. Using flow cytometry, we have previously shown that DN2, T-bet+, and CD11c+CD21- peripheral blood B cells correlate with interferon lambda (IFN-λ) serum levels, and numbers of ABC increase with SLE disease activity. An interferon stimulated gene (ISG) expression profile is found in many cell types in SLE, including B cells, and interferon is thought to be important to lupus pathogenesis. IFN-λ is known to generate an IFN signature similar to that of IFN alpha in epithelial cells, but few studies address IFN-λ effects on B cells. We hypothesized IFN-λ contributes to the gene expression profile seen in SLE and impacts B lymphocytes.

Methods: Human peripheral blood from healthy donors (n=6) or SLE (n=8) patients meeting ACR criteria were stained for CD11c, CD19, CD14, CD27 and IgD then flow sorted into CD14+ (monocytes), CD27- IgD- CD19+ (DN B cells), or CD27-IgD+ CD19+ (naïve B cells) populations and their RNA isolated for RNA-Seq transcriptomic analysis. B cells were cultured with IL-21, anti-Ig, R848 and BAFF to generate ABC-like cells in vitro with no IFN, interferon gamma (IFN-γ), IFN-λ1 or both for RNA isolation (4 hours) or flow cytometry (7 days). TBX21 (T-bet) and IFIT1 (an ISG) expression was measured by qRT-PCR. Cells were stained for CD3, CD11c, CD19, CD21, CD27, CD38, IgD and T-bet.

Results: Of the CD19+ cells used for transcriptional analysis, 5.2±3.0% of healthy donors and 9.6±7.9% of SLE B cells were CD11c+ as detected during the flow cytometry sort. Using RNA-Seq transcriptional analysis, IFN-λ receptor (IFNLR1) was expressed in B cells but was absent from monocytes. Expression in naïve B cells was 40 counts/million reads for healthy and 53 counts/million in SLE. The DN compartment had higher IFNLR1 expression with 66 counts/million in healthy and 131 counts/million in SLE. IFN-λ1 induced expression of IFIT1 in vitro suggesting that the IFN-λ receptor is indeed functional in B cells. When B cells were cultured in the presence of IFN-γ, TBX21 expression was strongly induced. IFN- λ1 could not be substituted for IFN-γ for the generation of CD11c+ CD21- cells as measured by flow cytometry or TBX21 expression at the RNA level. However, the combination of IFN-γ and IFN-λ1 resulted in an increased percentage of CD11c+ CD21- B cells at 7 days.

Conclusion: ABC are most represented in the DN2 B cell compartment. The DN2 B cells have the highest level of expression of IFNLR1. IFNLR1 is functional on B cells as ISG expression is increased when stimulated with IFN-λ1. Studies are ongoing to determine if IFN-λ1 has differential effects on different B cell compartments, alters B cell differentiation pathways including generation of autoreactive plasma cells (PC), or enhances ABC and PC survival, thus potentiating SLE disease pathogenesis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/interferon-lambda-promotes-age-associated-b-cells/