B-cell receptor for antigen modulates B-cell responses to complex TLR9 agonists and antagonists: implications for systemic lupus erythematosus

The capacity to make secondary structures significantly affects the ability of Toll-like receptor 9 (TLR9) agonists and antagonists to either induce or block TLR9-dependent activation in B cells. However, it has a minor impact on TLR9-induced activation in interferon alpha (IFNα)-producing dendritic cells. Based on the ability of inhibitory oligodeoxynucleotides to form predictable secondary structures, we have classified TLR9-antagonists into Class R ('restricted', palindromic) and Class B ('broadly reactive', linear) oligodeoxynucleotides. In non-autoreactive B cells, Class R oligodeoxynucleotides are at least 10-fold less potent TLR9-inhibitors. We wanted to determine whether engagement of the B-cell receptor for antigen could overcome this restriction. Here we show that in non-autoreactive mouse B cells, B-cell receptor for antigen engagement increased the potency of Class R oligodeoxynucleotides for TLR9 activation at least 10-fold, making it equal in potency to linear oligodeoxynucleotides. However, this enhanced potency was selective for TLR9-induced B-cell cycling and apoptosis protection while TLR9-induced IL-6, an event that strongly depends on signaling via late endosomes, still required 10 times more Class R oligodeoxynucleotides. Thus, pathway-specific effects of Class R oligodeoxynucleotides for TLR9/B-cell receptor for antigen co-stimulated B cells may have therapeutic advantages over non-selective targeting of B cells, a strategy that may be seen as a potential therapy for human systemic lupus erythematosus.