Which of the following could explain background staining caused by secondary or link antibodies cross-reacting with tissue antigens?

• A. Excessive washing steps.
• B. Secondary or link antibody cross-reacts with antigens from tissue specimen.
• C. Low pH buffer.
• D. Fresh reagents.

Answer: (B)

Background staining from immunohistochemistry often comes from the detector antibody binding to tissue components non-specifically. When the secondary or link antibody has affinity for antigens already present in the tissue—i.e., cross-reacts with tissue antigens—it will bind there and produce staining in areas where the target isn’t, creating background signal. This is exactly the situation described: the secondary antibody recognizing tissue antigens and yielding non-specific labeling. To reduce this, we use properly adsorbed or Fc-blocked secondary antibodies, thorough blocking with serum or protein solutions, and optimize antibody dilutions and incubation times. Excessive washing would typically lessen background rather than cause it; a low pH buffer or fresh reagents don’t inherently cause cross-reactivity with tissue antigens.