Cyclin D2 is essential for BCR-mediated proliferation and CD5 B cell development

Progression into G(1) in a lymphocytes is regulated by cyclins D2 and D3, c omponents of the cell cycle machinery currently believed to have overlappin g and potentially redundant roles in cell cycle control. To study the speci fic role of cyclin D2 in a lymphocyte proliferation, we examined a cells fr om cyclin D2(-/-) mice and demonstrate a specific requirement for cyclin D2 in BCR- but not CD40- or lipopolysaccharide-induced proliferation. Further more, conventional a cell development proceeds normally in the mutant mice; however, the CD5 B cell compartment is dramatically reduced, suggesting th at cyclin D2 is important in CD5 a cell development as well as antigen-depe ndent B cell clonal expansion.