transitional stage B cell T1 B cell A transitional stage B cell that migrates from the bone marrow into the peripheral circulation, and finally to the spleen. This cell type has the phenotype surface IgM-positive, surface IgD-negative, CD21-negative, CD23-negative, and CD62L-negative, and CD93-positive. This cell type has also been described as IgM-high, CD19-positive, B220-positive, AA4-positive, and CD23-negative. T1 B cells are also reportedly CD10-negative/positive??, CD20-positive, CD24-positive, CD38-positive, CD48-positive, CD84-positive, CD150-positive, CD244-negative, and CD352-positive. T1 B lymphocyte T1 B-cell T1 B-lymphocyte cell transitional stage 1 B cell