title: Cross-linking CD40 on human B cell precursors inhibits or enhances growth depending on the stage of development and the IL costimulus.
abstract: The function of the cell surface molecule CD40 on B cell precursors (BCP) is not well understood. We now report studies using the L cell/CD40 system (anti-CD40 mAb immobilized on CD32+ mouse L cells) to assess the potential function of CD40 during human B cell ontogeny. Stimulation of human B lineage cells with IL-4 in the L cell/CD40 system yielded a hierarchy of responsiveness: high density tonsillar B cells > fetal splenic B cells > fetal bone marrow surface Ig+ immature B cells > fetal bone marrow surface Ig- BCP. Using a microsphere/flow cytometry growth quantitation assay, we found that substituting IL-3 for IL-4 in the L cell/CD40 system provided a stronger growth stimulus for fetal bone marrow BCP and immature B cells. We also found that FACS-purified fetal bone marrow CD10+/CD34+/CD40+/cytoplasmic mu- pro-B cells responded maximally to IL-3 plus IL-7. Surprisingly, anti-CD40 inhibited the pro-B cell response to IL-7. In contrast, FACS-purified fetal bone marrow CD10+/CD34-/CD40+/cytoplasmic mu+ pre-B cells were essentially nonresponsive to IL-3, IL-7, or anti-CD40 alone, but were uniquely responsive to IL-3 plus anti-CD40. B-lineage cells derived after 14 days from IL-7-stimulated pro-B cells were predominantly CD19+/L chain-, whereas pre-B cells stimulated with IL-3 plus anti-CD40 were predominantly CD19+/L chain+. The L chain+ cells from pre-B cell cultures were both mu+/delta+ and mu-/delta+. Our results demonstrate that the response to CD40 signaling depends upon the BCP developmental stage and the IL costimulus, and indicate that normal human pro-B cells and pre-B cells have different growth factor requirements.
authors.affiliation: Department of Laboratory Medicine and Pathology, University of Minnesota Medical School, Minneapolis 55455.
authors.forename: A W
authors.initials: AW
authors.lastname: Larson
authors.forename: T W
authors.initials: TW
authors.lastname: LeBien
mesh_terms: D015703:Antigens, CD / Q000032:analysis / Q000502:physiology*; D018952:Antigens, CD34; D000944:Antigens, Differentiation, B-Lymphocyte / Q000502:physiology*; D001402:B-Lymphocytes / Q000502:physiology*; D019013:CD40 Antigens; D006412:Hematopoietic Stem Cells / Q000502:physiology*; D006801:Humans; D007143:Immunoglobulin Heavy Chains / Q000032:analysis; D007377:Interleukin-3 / Q000494:pharmacology; D015847:Interleukin-4 / Q000494:pharmacology; D015851:Interleukin-7 / Q000494:pharmacology; D007378:Interleukins / Q000494:pharmacology*; D008213:Lymphocyte Activation
chemical_list: D015703:Antigens, CD; D018952:Antigens, CD34; D000944:Antigens, Differentiation, B-Lymphocyte; D019013:CD40 Antigens; D007143:Immunoglobulin Heavy Chains; D007377:Interleukin-3; D015851:Interleukin-7; D007378:Interleukins; D015847:Interleukin-4