B-1 B cell progenitors transiently and partially express keratin 5 during differentiation in bone marrow

Abstract

BackgroundKeratin 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. ObjectiveHere we demonstrate an ectopic epidermal self-protein expression in B-1 B cell by fate mapping of K5-expressing cells. MethodsK5-Cre×CAG-CAT-loxP-EGFP double Tg (K5×GFP) mice that express enhanced GFP under the control of the K5 promoter were employed. ResultsUnexpectedly, B220+GFP+ cells were found in LN, spleen, peripheral blood and peritoneal cavity. These cells were IgM+IgDlowCD23−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+B220low−negCD19+ 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. ConclusionThese 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.