Alkaline phosphatase activity as a membrane marker for activated B cells.

Alkaline phosphatase activity was assayed by a microtiter assay (with p-nitrophenylphosphate used as substrate) in the plasma membrane of mouse spleen cells activated in vitro by the B cell mitogen LPS and the T cell-dependent B cell mitogen, PWM. No activity was detected in spleen cells cultured in the presence of the T cell mitogens PHA and Con A. This alkaline phosphatase activity was detected in the blast-enriched 30 to 40% fraction of discontinuous Percoll gradients in LPS-treated cultures, and the enzymatic activity assayed was susceptible to inhibition by the alkaline phosphatase inhibitors EDTA and L-phenylalanine. These data support the idea that the membrane alkaline phosphatase activity could be used as a marker for activated B cells.