B cell immature B cell An immature B cell is a precursor B cell that has the phenotype surface IgM-positive and surface IgD-negative, and have not undergone class immunoglobulin class switching or peripheral encounter with antigen and activation. Immature B cells are also reportedly CD5-positive, CD10-positive, CD19-positive, CD20-positive, CD21-positive, CD22-positive, CD24-positive, CD25-negative, CD27-negative, CD34-negative, CD38-positive, CD40-positive, CD43-negative, CD45-positive, CD48-positive, CD53-positive, CD79a-positive, CD80-negative, CD81-positive, CD86-negative, CD95-negative, CD127-negative, CD138-negative, CD185-positive, CD196-positive, MHCII/HLA-DR-positive, RAG-positive, TdT-negative, Vpre-B-negative, and preBCR-negative. Transcription factors expressed: Pax5-positive. cell immature B lymphocyte immature B-cell immature B-lymphocyte newly formed B cell