How are blocking peptides used in IHC?

• A. They neutralize the antibody by saturating the epitope recognized by the antibody.
• B. They enhance tissue fixation.
• C. They label the antibody with a dye.
• D. They prevent antigen retrieval.

Answer: (A)

Blocking peptides in IHC are used to test antibody specificity through competitive inhibition. By pre-incubating the antibody with a peptide that mimics the antigenic epitope, the antibody’s binding sites become occupied by the peptide. When this mixture is applied to tissue, the antibody can no longer bind the actual antigen, so staining is reduced or abolished. This demonstrates that the observed signal comes from specific recognition of that epitope. The other options don’t fit because blocking peptides aren’t used to enhance fixation, label the antibody, or prevent antigen retrieval; those roles are served by different steps or reagents in the protocol.