In an effort to determine the origin of natural antibodies to teichoic acid, rats were fed a sterile liquid diet free of detectable teichoic acid and virtually free of gram-positive bacteria. Both germ-free and conventional Sprague-Dawley rats raised on this diet failed to produce antibodies to polyglycerophosphate, whereas 100% of their counterparts fed the usual teichoic acid-containing diet did produce these antibodies. The intestinal flora was similar in both groups of animals. When the test animals were immunized intraperitoneally or orally with gram-positive bacteria, 100% displayed immunocompetency by producing significant levels of antibody. These results demonstrate the environmental nature of the antigenic stimulus for these antibodies and suggest the importance of food as the major source of stimulation. The experimental model described here furnishes a valuable tool for studies of immunologic responses where a single known specificity and a controlled system would be advantageous.
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