Ab0194 btla Expression Is Reduced on Sle B Cell Subsets

Abstract

BackgroundB- and T-lymphocyte attenuator (BTLA/CD272) is a co-receptor constitutively expressed on B cells [1, 2]. Upon B cell activation via the B cell receptor (BCR), BTLA co-localizes with Src homology region 2 domain-containing phosphatase-1 (SHP-1) and thus negatively regulates BCR signaling [2]. A recent study found that CD4+ T cells from SLE patients fail to upregulate BTLA upon activation [3], however, data on BTLA expression and function for B cells in autoimmunity is missing.ObjectivesTo assess BTLA expression on conventional naïve (CD20+CD27-), conventional memory (CD20+CD27+) B cells and on CD27++CD38++ expressing plasma cells (PC) in peripheral blood mononuclear cells (PBMCs) of patients with systemic lupus erythematosus (SLE) and healthy donors (HD).MethodsPBMCs were isolated from EDTA blood taken from 7 female SLE patients (age 38, mean disease activity 5 (SLEDAI)) and 6 female HD (mean age 28) by Ficoll density gradient centrifugation according to the manufacturer’s protocol. Cells have been stained and expression of BTLA was assessed by flow cytometry.ResultsAnalysis of BTLA surface expression on B cell subsets in SLE patients and HD revealed decreased expression of BTLA on naïve SLE B cells (*p=0.0173, Mann-Whitney U Test (MWU), BTLA median fluorescence intensity (MFI) 9006±1450) compared to naïve HD B cells (11957±941). A similar tendency was found for memory SLE B cells (p=0.0823 MWU) compared to HD memory but not SLE PC and HD PC. Remarkably, an inverse correlation was found for BTLA expression on naïve SLE B cells and SLE PC with Siglec-1 expression on monocytes (*p=0.0333 Spearman’s rank correlation (SRC) naïve B cells, *p=0.0167 PC), a marker for interferon signature, and the same trend was seen for SLE memory B cells (p=0.0583 SRC). Inverse correlation of BTLA expression was also found with disease activity (SLEDAI) with these B cell populations but did not reach significance (p=0.0583 naïve B cells, p=0.1361 memory B cells, p=0.0833 PC).ConclusionHerein, we document that B cell subsets of SLE patients express lower levels of the negative regulator BTLA than HD. Additionally, an inverse correlation between BTLA expression on B cell subsets and Siglec-1 on monocytes were found suggesting its involvement in disease and consideration BTLA as therapeutic target in SLE. We hypothesize that reduced BTLA expression is a feature of post-activated B cells. Further studies need to delineate functional properties of BTLA expression and activation in autoimmune B cells.References[1] Watanabe N, Gavrieli M, Sedy JR, Yang J, Fallarino F, Loftin SK, Hurchla MA, Zimmerman N, Sim J, Zang X, et al: BTLA is a lymphocyte inhibitory receptor with similarities to CTLA-4 and PD-1. Nat Immunol 2003, 4(7):670-679.[2] Vendel AC, Calemine-Fenaux J, Izrael-Tomasevic A, Chauhan V, Arnott D, Eaton DL: B and T lymphocyte attenuator regulates B cell receptor signaling by targeting Syk and BLNK. J Immunol2009, 182(3):1509-1517.[3] Sawaf M, Fauny JD, Felten R, Sagez F, Gottenberg JE, Dumortier H, Monneaux F: Defective BTLA...