title: Three restriction points in the cell cycle of activated murine B lymphocytes.
abstract: The cell cycle of activated B lymphocytes was found to be controlled by three restriction points. The first occurs immediately after mitosis and was found to be controlled by the binding of Sepharose-bound, immunoglobulin-specific antibodies to surface membrane-bound immunoglobulin. Exposure to this stimulus as short as 15 min or as long as 36 hr allowed B cells to move into the G1 phase up to the next restriction point. The second restriction point was observed to be approximately equal to 4 hr after mitosis, in the G1 phase of the cycle and 3-4 hr before the B cells entered S phase, and was found to be controlled by alpha-type B-cell growth factors produced by the P388D1 macrophage line. A third restriction point occurs in the G2 phase, 2-4 hr before mitosis, and is apparently controlled by beta-type B-cell growth factors that are likely to be produced by helper T lymphocytes.
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology* / Q000276:immunology; D002453:Cell Cycle; D006133:Growth Substances / Q000494:pharmacology; D015847:Interleukin-4; D008070:Lipopolysaccharides / Q000494:pharmacology; D008213:Lymphocyte Activation; D008222:Lymphokines / Q000494:pharmacology; D008285:Major Histocompatibility Complex; D051379:Mice; D008810:Mice, Inbred C57BL; D011947:Receptors, Antigen, B-Cell / Q000502:physiology
chemical_list: D006133:Growth Substances; D008070:Lipopolysaccharides; D008222:Lymphokines; D011947:Receptors, Antigen, B-Cell; D015847:Interleukin-4