title: Cell extrinsic alterations in splenic B cell maturation in Flt3-ligand knockout mice.
abstract: B lymphopoiesis in bone marrow (BM) is critical for maintaining a diverse peripheral B cell pool to fight infection and establish lifelong immunity. The generation of immature B cells is reduced in Flt3-ligand (FL-/-) mice leading to deficiencies in splenic B cells. Here, we sought to understand the cellular basis of the spleen B cell deficiency in FL-/- mice. Significant reductions in transitional (TS) and follicular (FO) B cells were found in FL-/- mice, and increased frequencies, but not absolute numbers, of marginal zone (MZ) B cells. BAFF-R expression on splenic B cells and serum levels of B cell activating factor (BAFF) was comparable to wildtype (WT) mice. Mixed BM chimeras revealed that the reductions in TS and FO B cells were cell extrinsic. FL administration into FL-/- mice restored the deficiency in TS B cells and normalized the MZ compartment. Ki67 analysis revealed a significant decrease in the proliferative capacity of TS B cells in FL-/- mice. A Bcl2 transgene did not rescue TS cells in FL-/- mice, uncoupling FL-deficiency to Bcl2-dependent survival pathways. Upregulation of CD1d expression and adoptive transfer experiments suggested MZ skewing in FL-/- mice. These findings support an integral role for Flt3 signaling in peripheral B cell maturation.
authors.affiliation: Department of Immunology, Mayo Clinic College of Medicine Rochester, MN, 55905.
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Dolence
authors.affiliation: Department of Immunology, Mayo Clinic College of Medicine Rochester, MN, 55905.
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Gwin
authors.affiliation: Department of Immunology, Mayo Clinic College of Medicine Rochester, MN, 55905.
authors.forename: Mariya B
authors.initials: MB
authors.lastname: Shapiro
authors.affiliation: Department of Immunology, Mayo Clinic College of Medicine Rochester, MN, 55905 ; Mayo Graduate School, Mayo Clinic College of Medicine Rochester, MN, 55905.
authors.forename: Fan-Chi
authors.initials: FC
authors.lastname: Hsu
authors.affiliation: Department of Immunology, Mayo Clinic College of Medicine Rochester, MN, 55905.
authors.forename: Virginia S
authors.initials: VS
authors.lastname: Shapiro
authors.affiliation: Department of Immunology, Mayo Clinic College of Medicine Rochester, MN, 55905.
authors.forename: Kay L
authors.initials: KL
authors.lastname: Medina
keywords: B cell maturation; B lymphopoiesis; BAFF; Flt3 signaling; follicular B cells; marginal zone B cells; proliferation; transitional B cells