A patient who received mouse monoclonal antibody therapy might show a false positive in a sandwich assay due to which reason?

The correct answer to the question is the presence of human anti-mouse antibody activity. When a patient receives mouse monoclonal antibody therapy, their immune system may recognize the mouse antibodies as foreign proteins, leading to the production of human anti-mouse antibodies (HAMAs). These antibodies can bind to the mouse monoclonal antibodies present in sandwich assays, which may result in a false positive result because they can interfere with the assay's ability to accurately detect the target antigen.

In the context of sandwich assays, which rely on the specific binding of antibodies to their target, the presence of HAMAs can disrupt this specificity. Instead of solely measuring the target antigen, the assay may also capture and detect the bound human anti-mouse antibodies, leading to an erroneously elevated signal that suggests the presence of more target antigen than is actually there.

Understanding that this interference occurs is crucial for interpreting immunological assays in patients who have undergone such therapies. It highlights the importance of recognizing and accounting for potential assay cross-reactivities due to therapeutic antibodies, ensuring accurate diagnostic results.