title: Possible role of tissue-bound calcium ions in citrate-mediated high-temperature antigen retrieval.
abstract: High-temperature preheating of sections in the presence of a salt (e.g., citrate) or a protein denaturant (e.g., urea) solution has been shown recently to provide a reliable alternative to tissue proteolysis for antigen retrieval from formaldehyde-fixed, paraffin-embedded tissues. However, the underlying mechanism of action of this form of pretreatment remains highly speculative. In this study, we show that calcium chelating agents such EDTA and EGTA are more effective than citrate in the retrieval of a citrate-sensitive nuclear antigen, Ki-67. Also, sodium carbonate and another calcium precipitating agent are both able to effect antigen retrieval at high temperatures. The overall data therefore suggest that either the chelation or the precipitation of tissue-bound calcium ions, and perhaps also other divalent metal cations, is a critical step in salt-mediated antigen retrieval. As a corollary, it is suggested that tight complexing of calcium ions or other divalent metal cations with proteins during formaldehyde tissue fixation is responsible for the masking of certain antigens.
authors.affiliation: Department of Histopathology, University Hospital of Wales, Heath Park, Cardiff, U.K.
authors.forename: J M
authors.initials: JM
authors.lastname: Morgan
authors.forename: H
authors.initials: H
authors.lastname: Navabi
authors.forename: K W
authors.initials: KW
authors.lastname: Schmid
authors.forename: B
authors.initials: B
authors.lastname: Jasani
mesh_terms: D000941:Antigens / Q000302:isolation & purification*; D002118:Calcium; D002254:Carbonates; D002413:Cations, Divalent; D002614:Chelating Agents; D002951:Citrates; D004492:Edetic Acid; D004533:Egtazic Acid; D005557:Formaldehyde; D006358:Hot Temperature; D006801:Humans; D007124:Immunoenzyme Techniques; D019394:Ki-67 Antigen; D009363:Neoplasm Proteins / Q000302:isolation & purification; D009687:Nuclear Proteins / Q000302:isolation & purification; D016612:Paraffin Embedding
chemical_list: D000941:Antigens; D002254:Carbonates; D002413:Cations, Divalent; D002614:Chelating Agents; D002951:Citrates; D019394:Ki-67 Antigen; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D005557:Formaldehyde; C005686:sodium carbonate; D004533:Egtazic Acid; D004492:Edetic Acid; D002118:Calcium