Regulation of autoreactive B cell responses to endogenous TLR ligands.

Immune complexes containing DNA and RNA are responsible for disease manifestations found in patients with systemic lupus erythematosus (SLE). B cells contribute to SLE pathology through BCR recognition of endogenous DNA- and RNA- associated autoantigens and delivery of these self-constituents to endosomal TLR9 and TLR7, respectively. B cell activation by these pathways leads to production of class-switched DNA- and RNA-reactive autoantibodies, contributing to an inflammatory amplification loop characteristic of disease.

Murine B cell response to TLR7 ligands depends on an IFN-beta feedback loop.

Type I IFNs play an important, yet poorly characterized, role in systemic lupus erythematosus. To better understand the interplay between type I IFNs and the activation of autoreactive B cells, we evaluated the effect of type I IFN receptor (IFNAR) deficiency in murine B cell responses to common TLR ligands. In comparison to wild-type B cells, TLR7-stimulated IFNAR(-/-) B cells proliferated significantly less well and did not up-regulate costimulatory molecules.

DNA-like class R inhibitory oligonucleotides (INH-ODNs) preferentially block autoantigen-induced B-cell and dendritic cell activation in vitro and autoantibody production in lupus-prone MRL-Fas(lpr/lpr) mice in vivo.

Introduction: B cells have many different roles in systemic lupus erythematosus (SLE), ranging from autoantigen recognition and processing to effector functions (for example, autoantibody and cytokine secretion). Recent studies have shown that intracellular nucleic acid-sensing receptors, Toll-like receptor (TLR) 7 and TLR9, play an important role in the pathogenesis of SLE. Dual engagement of rheumatoid factor-specific AM14 B cells through the B-cell receptor (BCR) and TLR7/9 results in marked proliferation of autoimmune B cells.

Autoreactive B cells discriminate CpG-rich and CpG-poor DNA and this response is modulated by IFN-alpha.

Autoreactive B cells are activated by DNA, chromatin, or chromatin-containing immune complexes (ICs) through a mechanism dependent on dual engagement of the BCR and TLR9. We examined the contribution of endogenous DNA sequence elements to this process. DNA sequence can determine both recognition by the BCR and by TLR9.

Functional outcome of B cell activation by chromatin immune complex engagement of the B cell receptor and TLR9.

We have previously shown that rheumatoid factors produced by Fas-deficient autoimmune-prone mice typically bind autologous IgG2a with remarkably low affinity. Nevertheless, B cells representative of this rheumatoid factor population proliferate vigorously in response to IgG2a/chromatin immune complexes through a mechanism dependent on the sequential engagement of the BCR and TLR9. To more precisely address the role of both receptors in this response, we analyzed the signaling pathways activated in AM14 B cells stimulated with these complexes.

DNA and RNA autoantigens as autoadjuvants.

AM14 B cells are a prototype for those low affinity autoreactive B cells that routinely mature as naïve cells in peripheral lymphoid tissues. These cells express a transgene-encoded receptor specific for IgG2a and can be effectively activated by immune complexes that incorporate either mammalian DNA or mammalian RNA that has been released from dead or dying cells. Activation depends on the ability of the B-cell receptor to deliver antigen to an internal vesicular compartment containing either Toll-like receptor-9 (TLR9) or TLR7.

Toll-like receptors, endogenous ligands, and systemic autoimmune disease.

The critical role of Toll-like receptors (TLRs) as mediators of pathogen recognition by the innate immune system is now firmly established. Such recognition results in the initiation of an inflammatory immune response and subsequent instruction of the adaptive immune system, both of which are designed to rid the host of the invading pathogen. More controversial is the potential role of TLRs in the recognition of endogenous ligands and what effect this might have on the consequent development of autoimmune or other chronic sterile inflammatory disorders.

Comparison of CpG s-ODNs, chromatin immune complexes, and dsDNA fragment immune complexes in the TLR9-dependent activation of rheumatoid factor B cells.

Synthetic single-stranded oligodeoxynucleotides (15-30 bp) containing CpG motifs and phosphorothioate backbones (CpG s-ODN), immune complexes consisting of anti-nucleosome mAbs and mammalian chromatin (chromatin IC), and immune complexes consisting of anti-hapten mAbs and haptenated-double stranded DNA fragments ( approximately 600 bp) can all effectively stimulate transgenic B cells expressing a rheumatoid factor receptor by a TLR9-dependent process. However, differential sensitivity to both s-ODN and small molecule inhibitors suggests that stimulatory CpG sODN and chromatin IC may either access TLR9 via different routes or depend on discrete activation parameters. These data have important implications regarding the therapeutic application of TLR9 inhibitors to the treatment of systemic autoimmune diseases.

The stimulation of Toll-like receptors by nuclear antigens: a link between apoptosis and autoimmunity.

As immunologists have long understood, effective responses to foreign antigens require adjuvants. It is now apparent that the initiation of autoimmune disease is comparably facilitated by adjuvant activity. In the case of antinuclear antibodies, it seems that DNA itself can serve as an endogenous adjuvant.