INHIBITION OF ENDOGENOUS-TISSUE ALKALINE-PHOSPHATASE WITH THE USE OF ALKALINE-PHOSPHATASE CONJUGATES IN IMMUNOHISTOCHEMISTRY

In mammals there are 2 forms of alkaline phosphatase, 1 which is widely distributed in a variety of tissues and 1 which is confined to intestine. Levamisole (1-tetramisole) inhibits the nonintestinal form of the enzyme, but is without effect on the intestinal form. This difference was exploited by using conjugates made with calf intestinal alkaline phosphatase for immunohistochemical demonstration of H2 antigens in frozen sections of mouse tissues. The alkaline phosphatase staining is performed in the presence of 1 mm levamisole, which inhibits the endogenous tissue enzyme without loss of staining by the conjugate. Endogenous enzyme can be inhibted by other means, such as exposure to 20% acetic acid, but labile antigens may be destroyed.