For immunofluorescence the tissue should be which of the following?

• A. Fresh or unfixed
• B. Fixed in formalin
• C. Paraffin embedded
• D. Heavily dehydrated

Answer: (A)

Immunofluorescence relies on preserving antigen structure so antibodies can bind with high affinity and the fluorescent label can be detected. Fresh or unfixed tissue, often prepared as cryosections, preserves antigenicity and allows antibodies to access epitopes without the masking that occurs during fixation. Formalin fixes proteins by cross-linking them, which can mask epitopes and diminish or alter the fluorescence signal; autofluorescence can also increase with some fixed tissues, complicating interpretation. Paraffin embedding requires dehydration and heating and generally reduces antigen accessibility unless specialized antigen-retrieval steps are used, which can still compromise fluorescence. Heavily dehydrated tissue is not suitable because it damages morphology and antigen integrity. So, the tissue should be fresh or unfixed to maintain proper antigenicity for immunofluorescence.