Aldehydes fixatives have which effect on antigenic sites and immunohistochemical localization of antigens?

• A. They mask antigenic sites and hamper IHC localization of antigens
• B. They enhance antigen localization
• C. They preserve all epitopes
• D. They do not affect antigenicity

Answer: (A)

Aldehyde fixatives work by cross-linking proteins in the tissue, which stabilizes structure but also creates barriers around antigenic epitopes. This cross-linking can mask sites that antibodies would normally recognize, making it harder for immunohistochemistry to bind and localize antigens. In practice, this means fixation preserves morphology but can reduce antigenicity, requiring antigen retrieval techniques (like heat or enzymatic treatment) to unmask epitopes and improve staining. Therefore, aldehyde fixatives tend to mask antigenic sites and hamper IHC localization of antigens.