Immunoalkaline phosphatase cytochemistry. Technical considerations of endogenous phosphatase activity

The authors have developed an immunoalkaline phosphatase method and have applied it with success to the study of blood cells. They have now observed that macrophages in tissues and in serous effusions may be nonspecifically stained when immunoalkaline phosphatase methods are used. A systematic study of this endogenous macrophage phosphatase activity has shown it to have a pH optimum of 5.0-6.0 (acid phosphatase), but it remains weakly active in the mildly alkaline conditions used in the immunoalkaline phosphatase procedure. At its pH optimum, this macrophage phosphatase is mostly tartrate resistant, however, when 50 mM tartrate is added to a staining medium of pH 7.6-8.0, the residual endogenous phosphatase activity effectively is inhibited. When immunochemical studies are conducted by immunoalkaline phosphatase methods, the authors recommend addition of 50 mM tartrate to a buffer of pH 7.6-8.0. This modification does not significantly decrease the sensitivity of the specific staining of surface antigens.