title: Receptor cross-talk spatially restricts p-ERK during TLR4 stimulation of autoreactive B cells.
abstract: To maintain tolerance, autoreactive B cells must regulate signal transduction from the BCR and TLRs. We recently identified that dendritic cells and macrophages regulate autoreactive cells during TLR4 activation by releasing IL-6 and soluble CD40 ligand (sCD40L). These cytokines selectively repress Ab secretion from autoreactive, but not antigenically naive, B cells. How IL-6 and sCD40L repress autoantibody production is unknown. In this work, we show that IL-6 and sCD40L are required for low-affinity/avidity autoreactive B cells to maintain tolerance through a mechanism involving receptor cross-talk between the BCR, TLR4, and the IL-6R or CD40. We show that acute signaling through IL-6R or CD40 integrates with chronic BCR-mediated ERK activation to restrict p-ERK from the nucleus and represses TLR4-induced Blimp-1 and XBP-1 expression. Tolerance is disrupted in 2-12H/MRL/lpr mice where IL-6 and sCD40L fail to spatially restrict p-ERK and fail to repress TLR4-induced Ig secretion. In the case of CD40, acute signaling in B cells from 2-12H/MRL/lpr mice is intact, but the chronic activation of p-ERK emanating from the BCR is attenuated. Re-establishing chronically active ERK through retroviral expression of constitutively active MEK1 restores tolerance upon sCD40L, but not IL-6, stimulation, indicating that regulation by IL-6 requires another signaling effector. These data define the molecular basis for the regulation of low-affinity autoreactive B cells during TLR4 stimulation; they explain how autoreactive but not naive B cells are repressed by IL-6 and sCD40L; and they identify B cell defects in lupus-prone mice that lead to TLR4-induced autoantibody production.
authors.affiliation: Department of Microbiology and Immunology, University of North Carolina, Chapel Hill, NC 27599, USA.
authors.forename: Sang-Ryul
authors.initials: SR
authors.lastname: Lee
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Rutan
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Monteith
authors.forename: Shannon Z
authors.initials: SZ
authors.lastname: Jones
authors.forename: Sun Ah
authors.initials: SA
authors.lastname: Kang
authors.forename: Kristen N
authors.initials: KN
authors.lastname: Krum
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Kilmon
authors.forename: Jose R
authors.initials: JR
authors.lastname: Roques
authors.forename: Nikki J
authors.initials: NJ
authors.lastname: Wagner
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Clarke
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Vilen
mesh_terms: D000818:Animals; D001323:Autoantibodies / Q000096:biosynthesis*; D016175:B-Lymphocyte Subsets / Q000276:immunology* / Q000378:metabolism* / Q000473:pathology; D019013:CD40 Antigens / Q000378:metabolism; D023201:CD40 Ligand / Q000378:metabolism; D002467:Cell Nucleus / Q000201:enzymology / Q000378:metabolism; D002478:Cells, Cultured; D018920:Coculture Techniques; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005260:Female; D007108:Immune Tolerance / Q000235:genetics; D008181:Lupus Nephritis / Q000201:enzymology / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D019463:Mice, Inbred MRL lpr; D008822:Mice, Transgenic; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D021381:Protein Transport / Q000235:genetics / Q000276:immunology; D020239:Receptor Cross-Talk / Q000276:immunology*; D011947:Receptors, Antigen, B-Cell / Q000502:physiology; D019947:Receptors, Interleukin-6 / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D051197:Toll-Like Receptor 4 / Q000502:physiology*
chemical_list: D001323:Autoantibodies; D019013:CD40 Antigens; D009687:Nuclear Proteins; D011947:Receptors, Antigen, B-Cell; D019947:Receptors, Interleukin-6; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D023201:CD40 Ligand; D048049:Extracellular Signal-Regulated MAP Kinases