Cell-Intrinsic Expression of TLR9 in Autoreactive B Cells Constrains BCR/TLR7-Dependent Responses

Abstract

Endosomal Toll-like receptors (TLRs) play an important role in systemic autoimmune diseases such as SLE, where DNA- and RNA-associated autoantigens activate autoreactive B cells through TLR9- and TLR7-dependent pathways. Nevertheless, TLR9-deficient autoimmune prone mice develop more severe clinical disease, while TLR7-deficient and TLR7/9-double deficient autoimmune-prone mice develop less severe disease. To determine whether the regulatory activity of TLR9 is B cell intrinsic, we have now directly compared the functional properties of autoantigen activated WT, TLR9-deficient and TLR7-deficient B cells, in an experimental system where proliferation depends on BCR/TLR co-engagement. In vitro, TLR9-deficient cells are less dependent on survival factors for a sustained proliferative response than either WT or TLR7-deficient cells. The TLR9-deficient cells also preferentially differentiate toward the plasma cell lineage, as indicated by expression of CD138, sustained expression of IRF4, and other molecular markers of plasma cells. In vivo, autoantigen-activated TLR9-deficient cells give rise to greater numbers of autoantibody producing cells. Our results identify distinct roles for TLR7 and TLR9 in the differentiation of autoreactive B cells that explain the capacity of TLR9 to limit, and TLR7 to promote, the clinical features of SLE.

A TLR9-dependent checkpoint governs B cell responses to DNA-containing antigens

“…Since T-bet + B cells have been reported in the context of aging, autoimmunity, and infections (74), these cells may arise in response to TLR9 ligands delivered via the BCR, and while such signals would ordinarily trigger apoptosis, cognate T cell help and additional cytokines could result in the breakthrough of autoantibody production. Additionally, in vivo and in vitro data suggest that RNA-sensing receptors, such as TLR7, do not promote post-proliferative cell death, but instead foster plasma cell differentiation (75). Thus, activation via these pathways may require concomitant TLR9 signals to control the overall response (30,33,76).…”

New insights into B cell biology in systemic lupus erythematosus and Sjögren's syndrome

“…An unsuspected tolerogenic role for TLR signaling was also supported by recent work demonstrating defective central and peripheral B cell tolerance checkpoints in patients deficient for interleukin-1 receptor-associated kinase 4 (IRAK-4), myeloid differentiation factor 88 (MyD88), and UNC-93B, key for signaling via multiple TLRs [29]. In mice, the exacerbation of clinical disease and production of anti-RNA antibodies in the absence of TLR9 was dependent on Type I IFN signaling [30] and was B cell intrinsic [31,32]. The enhanced production of anti-RNA antibodies is consistent with other data that TLR9 deficiency up-regulates TLR7 in B cells [33].…”

Autoreactive helper T cells alleviate the need for intrinsic TLR signaling in autoreactive B cell activation

“…AM14 Vκ8R, AM14 Vκ8R Tlr7 -/-, AM14 Vκ8R Tlr9 -/-, and AM14 Vκ8R Tlr7/9 -/-mice were described previously (10,19,45,46). DO11.10 Tcrα -/-BALB/c mice were previously described (18).…”

“…We used PL2-3, an antichromatin Ab that stimulates AM14 B cells in a TLR7-and TLR9-dependent manner (19), or Y2, an anti-Sm Ab precomplexed with Sm, which stimulates via TLR7 (20). Three days after the third round of stimulation, the cells were fused with BW5147 cells to generate T cell hybridomas, which were tested for reactivity to PL2-3 or Y2:Sm.…”