Endogenous avidin-binding activity in paraffin-embedded tissue revealed after microwave treatment

Heat-induced antigen retrieval has become a widely used method to enhance reactivity between antibodies and their epitopes in paraffin-embedded tissue sections. The formation of avidin-biotin complexes are used routinely to detect the presence of bound antibodies. We report the unmasking of endogenous avidin-binding activity in paraffin-embedded hepatic and renal tissue after microwave treatment, Incubation of sections with free biotin followed by avidin inhibits this endogenous avidin-binding activity and does not interfere with subsequent antibody staining reactions. These findings emphasize the need for appropriate negative controls and caution when interpreting results following heat-induced antigen retrieval methods.