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Abstract
An IgM-class rat monoclonal antibody, designated 5B1, was produced against rat carcinoembryonic antigen. This antibody, which can be considered an autoantibody, formed a single precipitation line in a gel diffusion test with an extract of the CEA-positive rat colonic adenocarcinoma, RCA-1. This line gave a reaction of complete identity with a line formed by a rabbit antiserum specific for rat CEA. 5B1 also bound to extracts of the RCA-1 tumor in EIA, but did not bind at all to extracts of the CEA-negative rat colonic adenocarcinoma, RCA-2, nor to extracts of normal rat tissues including liver, kidney and intestine. Inhibition tests showed that the activity of the monoclonal antibody in EIA was abolished by extracts of RCA-1 tumor, but was hardly affected by extracts of the other tissues.