Primary Development and Participation in a Foreign Antigen-Driven Immune Response of a Chromatin-Reactive B Cell Clonotype Are Not Influenced by TLR9 or Other MyD88-Dependent TLRs

Recent findings support a central role for TLRs in both foreign Ag-driven immune responses and systemic autoimmune diseases mediated by B lymphocytes. In vitro studies have shown that the Ag receptors (BCRs) on B cells specific for nuclear autoantigens can facilitate the delivery of these autoantigens to the endocytic compartment, resulting in activation of the nucleic acid-specific TLRs present in this subcellular locale. If this pathway is operative in vivo it might promote the development, survival, or activation of such autoreactive B cells. To test this idea, we evaluated the influence of a deficiency in the CpG DNA-specific TLR, TLR9, or all MyD88-dependent TLRs on the primary development and foreign Ag-driven immune response of B cells in a line of V(H) knockin mice that contains a high frequency of "dual reactive" B cells specific for DNA-based autoantigens such as chromatin, as well as the hapten arsonate. We found that although development and activation of these B cells in vitro are clearly influenced by DNA-based autoantigens, TLR9 or MyD88 deficiencies had no apparent effect on the primary development and participation in the anti-arsonate response of these B cells in vivo. We discuss these results in the context of previous models for the role of TLR9 and other TLRs in the regulation of antinuclear Ag B cell development and activity.