Blocking of endogenous avidin-binding activity in immunohistochemistry - The use of skim milk as an economical and effective substitute for commercial biotin solutions

Endogenous avidin-binding activity (EABA), usually due to the presence of e ndogenous biotin in tissues, can be a bothersome artifact in immunohistoche mistry when avidin-biotin- or streptavidin-biotin-based detection systems a re used (1). EABA may be markedly enhanced by heat-induced epitope retrieva l (HIER) procedures (2,3), and the increasing use of HIER has made EABA mor e of a problem than in the past. Traditionally, EABA has been blocked by in cubating sections with avidin solution followed by biotin solution, immedia tely before the primary antibody incubation step (1). Commercially availabl e avidin is expensive, and we previously showed that dilute egg whites are an economical and effective substitute for commercial avidin solutions in E ABA-blocking procedures (2). After discovering that milk is rich in biotin (4), we hypothesized that milk might be a useful substitute for commerciall y obtained biotin for EABA-blocking procedures. In this brief report, we de monstrate that skim milk is an effective and economical alternative to comm ercially available biotin for use in EABA-blocking procedures.