B cell mature B cell A B cell that is mature, having left the bone marrow. Initially, these cells are IgM-positive and IgD-positive, and they can be activated by antigen. mature B-lymphocyte mature B lymphocyte mature B-cell Mature B cells are also reportedly CD10-negative, CD19-positive, CD22-positive, CD34-negative, CD48-positive, CD79a-positive, CD84-positive, CD127-negative, CD352-positive, RAG-negative, TdT-negative, Vpre-B-negative, and pre-BCR-negative. Transcription factors expressed: Pax5-positive. B cell, CD19-positive