IDENTIFICATION OF ENDOGENOUS PEROXIDASE-CONTAINING CELLS AS EOSINOPHILS IN THE GASTROINTESTINAL SYSTEM

Endogenous peroxidase (EPX) activity in certain cells in the gastroint estinal system interferes with immunohistochemical methods based on th e horseradish peroxidase-catalyzed substrate deposition. We studied th e distribution and characteristics of these cells. We also report an e ffective and antigen-preserving EPX blocking method, to make possible the evaluation of immunoperoxidase stainings in cryostat sections. The EPX-containing cells (EPX cells) are present in every part of the gas trointestinal tract, predominantly in the tunica propria. We identifie d them as eosinophil cells in May-Grunwald-Giemsa stained sections. Th e complete match was confirmed by different fluorescence techniques. F irstly, the EPX cells were labeled by a red fluorochrome-conjugated su bstrate of peroxidase enzymes, rhodamine-tyramide, whereas the eosinop hil cells were labeled by the green fluorochrome, 1-hydroxy-3,6,8-pyre netrisulfonic acid, which is known to label exclusively eosinophilic g ranules at pH 10. Secondly, all the EPX cells reacted with a monoclona l antibody against the eosinophil peroxidase enzyme. Finally, a set of commercially available leukocyte markers was used to characterize the EPX cells colabeled by fluorochrome-tyramides. Neither macrophages no r mast cells showed EPX activity. Increased numbers and altered distri bution were seen in stressed rats and in ulcerated human stomach.