This flow cytometric B-cell panel, using a combination of conjugated monoclonal antibodies, is intended to provide a global overview of B-cell development and differentiation. Using specific combinations of surface markers, its goal is to detect defects in the normal sequence of maturation and differentiation through the absence of certain subpopulations, and/or the presence of unusual populations (e.g. transitional B cells), not normally found in peripheral blood. In addition, aberrant B-cell function may be detected by alterations in the normal distribution of B-cell populations, including plasma-blasts. In conjunction with other laboratory data, as well as clinical information, this assay can assist in providing a more detailed picture of the B-cell compartment and its context with the overall immune system.

CD10+ B cells reflect immature B cells prior to the stage of transitional B cells. Transitional B cells can be characterized by lack of CD27 and CD21, and high levels of CD38 and IgM. Mature, naïve B cells are CD27 negative, CD21 positive, and IgM and IgD positive. Peripheral blood memory B cells are CD27 positive, and can be further classified as non-switched memory (IgM positive and IgD positive or negative), or switched memory (IgM and IgD negative). Expression of CD5 on B cells may indicate a specific B-cell lineage or an in vivo activated B cell subset. Activated circulating B cells, as well as terminally differentiated plasma-blasts and early plasma cells can be identified on the basis of CD38 and CD138 expression and down-regulation of CD19 expression (CD20 expression is already lost at this stage).