title: PP4 is essential for germinal center formation and class switch recombination in mice.
abstract: PP4 is a serine/threonine phosphatase required for immunoglobulin (Ig) VDJ recombination and pro-B/pre-B cell development in mice. To elucidate the role of PP4 in mature B cells, we ablated the catalytic subunit of murine PP4 in vivo utilizing the CD23 promoter and cre-loxP recombination and generated CD23(cre)PP4(F/F) mice. The development of follicular and marginal zone B cells was unaffected in these mutants, but the proliferation of mature PP4-deficient B cells stimulated by in vitro treatment with either anti-IgM antibody (Ab) or LPS was partially impaired. Interestingly, the induction of CD80 and CD86 expression on these stimulated B cells was normal. Basal levels of serum Igs of all isotypes were strongly reduced in CD23(cre)PP4(F/F) mice, and their B cells showed a reduced efficiency of class switch recombination (CSR) in vitro upon stimulation by LPS or LPS plus IL-4. When CD23(cre)PP4(F/F) mice were challenged with either the T cell-dependent antigen TNP-KLH or the T cell-independent antigen TNP-Ficoll, or by H1N1 virus infection, the mutant animals failed to form germinal centers (GCs) in the spleen and the draining mediastinal lymph nodes, and did not efficiently mount antigen-specific humoral responses. In the resting state, PP4-deficient B cells exhibited pre-existing DNA fragmentation. Upon stimulation by DNA-damaging drug etoposide in vitro, mutant B cells showed increased cleavage of caspase 3. In addition, the mutant B cells displayed impaired CD40-mediated MAPK activation, abnormal IgM-mediated NF-κB activation, and reduced S phase entry upon IgM/CD40-stimulation. Taken together, our results establish a novel role for PP4 in CSR, and reveal crucial functions for PP4 in the maintenance of genomic stability, GC formation, and B cell-mediated immune responses.
authors.affiliation: Immunology Research Center, National Health Research Institutes, Zhunan, Miaoli County, Taiwan.
authors.forename: Ming-Yu
authors.initials: MY
authors.lastname: Chen
authors.affiliation: Immunology Research Center, National Health Research Institutes, Zhunan, Miaoli County, Taiwan.
authors.forename: Ya-Ping
authors.initials: YP
authors.lastname: Chen
authors.affiliation: National Institute of Infectious Diseases and Vaccinology, National Health Research Institutes, Zhunan, Miaoli County, Taiwan.
authors.forename: Ming-Sian
authors.initials: MS
authors.lastname: Wu
authors.affiliation: National Institute of Infectious Diseases and Vaccinology, National Health Research Institutes, Zhunan, Miaoli County, Taiwan.
authors.forename: Guanni-Yi
authors.initials: GY
authors.lastname: Yu
authors.affiliation: Immunology Research Center, National Health Research Institutes, Zhunan, Miaoli County, Taiwan.
authors.forename: Wen-Jye
authors.initials: WJ
authors.lastname: Lin
authors.affiliation: Immunology Research Center, National Health Research Institutes, Zhunan, Miaoli County, Taiwan; Department of Pathology & Immunology, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Tse-Hua
authors.initials: TH
authors.lastname: Tan
authors.affiliation: Immunology Research Center, National Health Research Institutes, Zhunan, Miaoli County, Taiwan.
authors.forename: Yu-Wen
authors.initials: YW
authors.lastname: Su
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001402:B-Lymphocytes / Q000276:immunology*; D019013:CD40 Antigens / Q000096:biosynthesis / Q000276:immunology; D004249:DNA Damage / Q000187:drug effects; D053938:DNA Fragmentation / Q000187:drug effects; D005047:Etoposide / Q000008:administration & dosage; D018858:Germinal Center / Q000276:immunology; D007113:Immunity, Innate / Q000235:genetics / Q000276:immunology*; D017578:Immunoglobulin Class Switching / Q000235:genetics / Q000276:immunology*; D007075:Immunoglobulin M / Q000235:genetics / Q000276:immunology; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics / Q000276:immunology; D008070:Lipopolysaccharides / Q000008:administration & dosage; D051379:Mice; D016328:NF-kappa B / Q000235:genetics / Q000276:immunology; D010749:Phosphoprotein Phosphatases / Q000235:genetics* / Q000276:immunology; D013154:Spleen / Q000187:drug effects / Q000276:immunology; D060152:V(D)J Recombination / Q000235:genetics* / Q000276:immunology
chemical_list: D019013:CD40 Antigens; D007075:Immunoglobulin M; D008070:Lipopolysaccharides; D016328:NF-kappa B; D005047:Etoposide; D010749:Phosphoprotein Phosphatases; C080406:protein phosphatase 4