Phenotypic expression of B lymphocytes. III. Marginal zone B cells in the spleen are characterized by the expression of Tac and alkaline phosphatase.

The marginal zone of the spleen contains lymphocytes with an intermediate morphologic form between small lymphocytes and plasmablasts. The majority of cells can be stained by B cell monoclonal antibodies including B1, Leu-14, and Leu-12. The most significant finding is the expression of an interleukin 2 receptor (Tac) and an enzyme-alkaline phosphatase by the marginal zone B lymphocytes. The Tac antigen is not normally present in B cells, but can be found in a portion of in vitro-activated B lymphocytes. In conjunction with other evidence, the marginal zone B lymphocytes may represent the activated B cells in the early stages of B cells differentiation. Alternatively, the Tac-positive, marginal zone B lymphocytes may be a discrete subpopulation of activated B cells.