Influence of methacarn fixation on immunohistochemistry

Immunohistochemistry (IHC) is widespread technique used in many laboratories for diagnostic and research purposes. Fixation of tissue is important, but very often neglegted methodical part of IHC. It is known, that fixation may compromise the final outcome of IHC. Although, formol (10% solution of formalin in water) represents gold standart of fixatives, other solutions are sometimes used. Methacarn (methanol, acetic acid, chloroform (6:1:3)) is used in methods which isolation of DNA and mRNA are needed. It is also used as alternative fixative for IHC. It is non-cross-linking fixative, thus heat induced epitope retrieval is not required before immunostaining.

However, we detect discrepances in IHC results in human embryonic kidney samples (n = 21) fixed in formol or methacarn stained for protein CYP2C9, member of cytochrome P450 superfamily related to metabolism of both xenobiotic and endogenous compounds. Formol-fixed tissues shows positivity mainly in tubular system, whereas methacarn-fixed samples has strong positivity in conective tissue and very low or no positivity in tubular system. Therefore, even if some studies have found no differencies between formol and methacarn fixation, their influence should be considered in diagnostic and research applications.