title: Constitutive CD40 Signaling Calibrates Differentiation Outcomes in Responding B Cells via Multiple Molecular Pathways.
abstract: CD40 signaling during B cell activation is known to inhibit terminal differentiation and promote memory generation. Blimp-1 is essential for efficient plasma cell (PC) generation, and although CD40 signaling is known to inhibit Blimp-1 induction during B cell activation, the mechanisms involved have been unclear. We report that CD40 signaling induces miR-125b that targets Blimp-1 transcripts, and increases amounts of the ubiquitin ligase Hrd1 that targets BLIMP-1 protein for proteasomal degradation. CD40 signaling also inhibits the early unfolded protein response (UPR) of activated B cells that precedes the induction of terminal differentiation, and Hrd1 feeds into this pathway by targeting the core UPR component IRE-1α. Strikingly, CD40 signaling in the absence of BCR- or TLR-ligation also repressed Blimp-1 transcripts, suggesting that noncognate ligation of CD40 via T-B interactions may repress Blimp-1 in vivo. In support of this, we find that naive B cells purified from CD40-CD154 interaction-deficient mice express higher amounts of Blimp-1 and lower amounts of microRNAs and Hrd1. Higher basal amounts of Blimp-1 in naive CD40(-/-) B cells correlate with an increased tendency of the cells to undergo terminal differentiation upon LPS stimulation. Conversely, a 24-h exposure to CD40 ligation during LPS stimulation of wild-type B cells is sufficient to inhibit PC generation. The data show that CD40-mediated inhibition of PC generation is via engagement of multiple pathways that involve repression of Blimp-1 and inhibition of the UPR that prepares cells to become professional secretors. They also show that constitutive CD40 signaling in vivo involving bystander T-B interactions can calibrate B cell differentiation outcomes.
authors.affiliation: National Institute of Immunology, New Delhi 110067, India; and.
authors.forename: Srijani
authors.initials: S
authors.lastname: Basu
authors.affiliation: National Institute of Immunology, New Delhi 110067, India; and.
authors.forename: Sheetal
authors.initials: S
authors.lastname: Kaw
authors.affiliation: National Institute of Immunology, New Delhi 110067, India; and.
authors.forename: Lucas
authors.initials: L
authors.lastname: D'Souza
authors.affiliation: Council of Scientific and Industrial Research, Centre for Cellular and Molecular Biology, Hyderabad 500007, India.
authors.forename: Tushar
authors.initials: T
authors.lastname: Vaidya
authors.affiliation: National Institute of Immunology, New Delhi 110067, India; and.
authors.forename: Vineeta
authors.identifier: 0000-0002-8995-2045
authors.initials: V
authors.lastname: Bal
authors.affiliation: National Institute of Immunology, New Delhi 110067, India; and.
authors.forename: Satyajit
authors.initials: S
authors.lastname: Rath
authors.affiliation: National Institute of Immunology, New Delhi 110067, India; and anna@nii.res.in.
authors.forename: Anna
authors.initials: A
authors.lastname: George
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology; D019013:CD40 Antigens / Q000276:immunology / Q000378:metabolism*; D002454:Cell Differentiation / Q000276:immunology*; D005434:Flow Cytometry; D008213:Lymphocyte Activation / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010950:Plasma Cells / Q000166:cytology* / Q000276:immunology; D000074462:Positive Regulatory Domain I-Binding Factor 1; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction / Q000276:immunology*; D014157:Transcription Factors / Q000276:immunology / Q000378:metabolism
chemical_list: D019013:CD40 Antigens; C513258:Prdm1 protein, mouse; D014157:Transcription Factors; D000074462:Positive Regulatory Domain I-Binding Factor 1