Objective: Immunohistochemical investigation of archival histological material is a serious problem, since long-term storage of biological tissues, most often in formalin, leads to a loss of antigenic properties. However, the biological material can also be stored in the clearing agent methyl salicylate. The aim of this study was to assess the antigenicity of the human choroid plexus after extra long-term storage in methyl salicylate.

Material and Method: The study was performed on samples of fixed human choroid plexus (occasionally with attached neighboring pineal gland) stored in either methyl salicylate or paraffin blocks for 25 years. Chromogenic and fluorescence immunohistochemistry of vimentin, GFAP, type IV collagen, β-catenin, α-smooth muscle actin, von Willebrand factor, CD68, mast cell tryptase, TMEM119, and synaptophysin was carried out.

Results: The storage of human choroid plexus in methyl salicylate for 25 years does not impair its histomorphology and preserves the properties of all the antigens assessed, which makes their immunohistochemical visualization possible using both light and fluorescence microscopy. Additionally, we found that long-term storage of human choroid plexus in methyl salicylate does not cause an increase in autofluorescence.

Conclusion: Methyl salicylate can be recommended as a medium for long-term storage of biological tissue, as it provides excellent brain tissue preservation and retains its antigenic properties for up to 25 years.