title: B-1 B cell progenitors transiently and partially express keratin 5 during differentiation in bone marrow.
abstract: BACKGROUND
  Keratin 5 (K5) is a cytoskeletal tissue-specific protein expressed in the epithelial cells of skin and esophagus and ectopic K5 expression in lymphocytes has never been reported.
  
  
  OBJECTIVE
  Here we demonstrate an ectopic epidermal self-protein expression in B-1 B cell by fate mapping of K5-expressing cells.
  
  
  METHODS
  K5-Cre×CAG-CAT-loxP-EGFP double Tg (K5×GFP) mice that express enhanced GFP under the control of the K5 promoter were employed.
  
  
  RESULTS
  Unexpectedly, B220(+)GFP(+) cells were found in LN, spleen, peripheral blood and peritoneal cavity. These cells were IgM(+)IgD(low)CD23(-)CD43(+)CD19(+)CD93(-), indicating that they were B-1 B cells. The number of B220(+)GFP(+) cells was significantly larger in spleen than in the other tissues tested. Although GFP(+) B-1 cells did not express K5 in the periphery, Lin(-)CD93(+)B220(low-neg)CD19(+) B-1 B cell progenitors expressed GFP and B220(+)CD93(+) progenitor cells expressed K5 and MHC-class II in BM, indicating that GFP(+) B-1 cells transiently expressed K5 and the progenitor cells were potential APC. GFP(+) B-1 cells in the periphery continued expressing MHC class II and had exogenous antigen-presenting capacity comparable to non-follicular B cells. GFP(+) B-1 cells spontaneously secreted more IgM than GFP(-) B-1 cells in vitro.
  
  
  CONCLUSIONS
  These results indicate that B-1 B cells transiently and partially express K5 in BM and are potent for both natural antibody production and antigen presentation.
authors.affiliation: Department of Dermatology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan; Department of Dermatology, Tokyo Medical and Dental University, Yushima 1-5-45, Bunkyo-ku, Tokyo 113-8519, Japan. Electronic address: takafussa0710@gmail.com.
authors.forename: Takaaki
authors.initials: T
authors.lastname: Hanafusa
authors.affiliation: Department of Dermatology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan. Electronic address: bykenbykenbyken@yahoo.co.jp.
authors.forename: Kenichi
authors.initials: K
authors.lastname: Kato
authors.affiliation: Department of Dermatology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan; Department of Dermatology, Nara Medical University, 840, Shijo-cho, Kashihara, Nara 634-8521, Japan. Electronic address: azukizaw@derma.med.osaka-u.ac.jp.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Azukizawa
authors.affiliation: Division of Stem Cell Regulation Research, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan. Electronic address: jimiyaza@nutri.med.osaka-u.ac.jp.
authors.forename: Jun-ichi
authors.initials: J
authors.lastname: Miyazaki
authors.affiliation: Center for Advanced Science and Innovation & Department of Social and Environmental Medicine, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan. Electronic address: takeda@mr-envi.med.osaka-u.ac.jp.
authors.forename: Junji
authors.initials: J
authors.lastname: Takeda
authors.affiliation: Department of Dermatology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan. Electronic address: katayama@derma.med.osaka-u.ac.jp.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Katayama
mesh_terms: D000818:Animals; D000917:Antibody Formation; D017951:Antigen Presentation; D015415:Biomarkers / Q000378:metabolism; D001854:Bone Marrow Cells / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D002454:Cell Differentiation; D019070:Cell Lineage; D002478:Cells, Cultured; D005838:Genotype; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007075:Immunoglobulin M / Q000096:biosynthesis; D053569:Keratin-15 / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010641:Phenotype; D054448:Precursor Cells, B-Lymphoid / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D013997:Time Factors
chemical_list: D015415:Biomarkers; D007075:Immunoglobulin M; D053569:Keratin-15; C492053:Krt15 protein, mouse; D008070:Lipopolysaccharides; C485184:enhanced green fluorescent protein; C433788:lipopolysaccharide, E. coli O26-B6; D049452:Green Fluorescent Proteins
keywords: Antigen-presenting cells; B cell development; B-1 B cell; Epidermal self-protein; Self/non-self discrimination