title: Distinct activation signals determine whether IL-21 induces B cell costimulation, growth arrest, or Bim-dependent apoptosis.
abstract: IL-21 costimulates B cell proliferation and cooperatively with IL-4 promotes T cell-dependent Ab responses. Somewhat paradoxically, IL-21 also induces apoptosis of B cells. The present study was undertaken to more precisely define the expression of the IL-21R, using a novel mAb, and the circumstances by which IL-21 promotes B cell growth vs death. The IL-21R was first detected during T and B cell development, such that this receptor is expressed by all mature lymphocytes. The IL-21R was further up-regulated after B and T activation, with the highest expression by activated B cells. Functional studies demonstrated that IL-21 substantially inhibited proliferation and induced Bim-dependent apoptosis for LPS or CpG DNA-activated B cells. In contrast, IL-21 induced both costimulation and apoptosis for anti-CD40-stimulated B cells, whereas IL-21 primarily costimulated B cells activated by anti-IgM or anti-IgM plus anti-CD40. Upon blocking apoptosis using C57BL/6 Bim-deficient or Bcl-2 transgenic B cells, IL-21 readily costimulated responses to anti-CD40 while proliferation to LPS was still inhibited. Engagement of CD40 or the BCR plus CD40 prevented the inhibitory effect by IL-21 for LPS-activated B cells. Collectively, these data indicate that there are three separable outcomes for IL-21-stimulated B cells: apoptosis, growth arrest, or costimulation. We favor a model in which IL-21 promotes B cell maturation during a productive T cell-dependent B cell response, while favoring growth arrest and apoptosis for nonspecifically or inappropriately activated B cells.
authors.affiliation: Department of Microbiology and Immunology, University of Miami School of Medicine, Miami, FL 33101, USA.
authors.forename: Haoli
authors.initials: H
authors.lastname: Jin
authors.forename: Roberto
authors.initials: R
authors.lastname: Carrio
authors.forename: Aixin
authors.initials: A
authors.lastname: Yu
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Malek
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins; D001402:B-Lymphocytes / Q000187:drug effects* / Q000276:immunology / Q000502:physiology; D000072224:Bcl-2-Like Protein 11; D019013:CD40 Antigens / Q000502:physiology; D002352:Carrier Proteins / Q000502:physiology*; D002453:Cell Cycle; D002478:Cells, Cultured; D053738:Interleukin-21 Receptor alpha Subunit; D007378:Interleukins / Q000494:pharmacology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008213:Lymphocyte Activation; D008565:Membrane Proteins / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051381:Rats; D011947:Receptors, Antigen, B-Cell / Q000502:physiology; D018123:Receptors, Interleukin / Q000502:physiology; D053655:Receptors, Interleukin-21; D000098546:Interleukin-21
chemical_list: D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; C000606778:Bcl2l11 protein, rat; D019013:CD40 Antigens; D002352:Carrier Proteins; C508118:Il21r protein, mouse; D053738:Interleukin-21 Receptor alpha Subunit; D007378:Interleukins; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D011947:Receptors, Antigen, B-Cell; D018123:Receptors, Interleukin; D053655:Receptors, Interleukin-21; D000098546:Interleukin-21