Which statement is true regarding antigenicity in unfixed tissue?

• A. Loss of antigenicity in unfixed tissue.
• B. Unfixed tissue has maximum antigenicity.
• C. Antigenicity is unaffected by fixation.
• D. Antigenicity is present only after staining.

Answer: (A)

Antigenicity is about how accessible the epitope is to antibodies. In unfixed tissue, there are no fixative-induced cross-links, so epitopes remain accessible and antigenicity is typically preserved, often at its highest level. Fixation, especially with formalin, creates cross-links that mask epitopes and reduce antigenicity; after fixation, many protocols use antigen retrieval to unmask these sites and restore recognition by antibodies. Staining itself does not create antigenicity, it simply reveals what is already present. So the idea that antigenicity is lost in unfixed tissue isn’t accurate—the opposite is true: unfixed tissue generally retains maximum antigenicity, while fixation can diminish it.