Cellular enzyme-linked immunospecific assay (CELISA). IV. Inhibition of endogenous cellular alkaline phosphatase activity.

The cellular enzyme-linked immunospecific assay (CELISA) uses ligands conjugated to calf intestinal alkaline phosphatase to quantitate antibody bound to antigens on the surfaces of whole cells. Since the endogenous alkaline phosphatase present in many cell types contributes unwanted background noise to the assay, ways of inhibiting endogenous cellular alkaline phosphatase were investigated. We found that the endogenous alkaline phosphatase in human peripheral blood mononuclear cells was incompletely inhibited by EDTA or L-cysteine. Levamisole, however, inhibited endogenous cellular alkaline phosphatase completely without impairing the sensitivity of the CELISA. The use of levamisole is recommended for assays that use alkaline phosphatase conjugates to detect molecules on the surfaces of cells that also contain endogenous alkaline phosphatase.