What does it indicate when a staining reaction is observed despite using a blocking peptide in an IHC protocol?

What does it indicate when a staining reaction is observed despite using a blocking peptide in an IHC protocol?

• A. Specific staining
• B. Non-specific staining or false positive staining
• C. Tissue degradation
• D. Complete absence of signal

Answer: (B)

The blocking peptide is used to test whether the antibody’s binding is truly specific to the target antigen. If staining is still seen after pre-absorption with the blocking peptide, it means the signal is not due to the specific antigen–antibody interaction but to non-specific binding or cross-reactivity. In other words, it’s a false positive: the antibody or detection system is producing a signal through other interactions (such as binding to other proteins, Fc receptors, secondary antibody cross-reactivity, or endogenous enzymes) rather than the intended target. This contrasts with true specific staining, which should be eliminated or greatly diminished when the antibody is blocked.

The blocking peptide is used to test whether the antibody’s binding is truly specific to the target antigen. If staining is still seen after pre-absorption with the blocking peptide, it means the signal is not due to the specific antigen–antibody interaction but to non-specific binding or cross-reactivity. In other words, it’s a false positive: the antibody or detection system is producing a signal through other interactions (such as binding to other proteins, Fc receptors, secondary antibody cross-reactivity, or endogenous enzymes) rather than the intended target. This contrasts with true specific staining, which should be eliminated or greatly diminished when the antibody is blocked.