Crude extracts of uropathic Escherichia coli have been reported to inhibit the binding of human Tamm-Horsfall protein (THP) to homologous and heterologous anti-THP antibody in immunoassays. This phenomenon was believed to be due to immunologic cross reactivity between THP and the bacterial antigens for the same antibody. Our attempts to further purify and characterize these 'cross reactive' antigens with ion exchange and molecular sieve chromatography were unsuccessful. When purified anti-THP antibody was conjugated to sepharose beads forming an immunoadsorption column capable of isolating THP and cross reactive antigens from solution, the bacterial extracts did not react with the affinity column. However, binding between THP and the bacterial extracts and between THP and whole bacteria were demonstrated. These findings suggest that the cross reactivity seen in the immunoassays is caused by the interaction between the bacterial extracts and THP, and is not representative of true immunologic cross reaction for a common antibody.
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