What is the fixative for immunofluorescence?

• A. Frozen, no fixation
• B. Formalin
• C. Bouin
• D. Glutaraldehyde

Answer: (A)

Immunofluorescence relies on preserving antigen sites and the fluorescent signal. Crosslinking fixatives like formalin, Bouin, and glutaraldehyde bind proteins and can mask epitopes, increasing background autofluorescence and reducing antibody binding. To keep antigenicity intact and maximize fluorescence, immunofluorescence is typically performed on unfixed, fresh-frozen tissue (or with precipitating fixatives such as cold acetone or methanol that don’t crosslink proteins). Therefore, using frozen tissue with no fixation best preserves the antigen sites and fluorescence needed for immunofluorescence signals. If fixation is used, a non-crosslinking, cold precipitating fixative is preferred over formalin or glutaraldehyde.