Which of the following limits the effectiveness of monoclonal antibodies in hemagglutination assays?

The effectiveness of monoclonal antibodies in hemagglutination assays is indeed limited by their specificity, which is represented in the choice stating that they react with only one antigenic determinant. Monoclonal antibodies are designed to bind to a specific epitope on an antigen, which means they target only a single type of antigenic determinant.

In hemagglutination assays, the presence of multiple antigens or the need to crosslink red blood cells can require antibodies that can bind to multiple sites or different determinants on the same target molecule. The specificity of monoclonal antibodies to a single epitope can limit their ability to form the necessary bridging interactions between red blood cells and antigens, which is essential for effective agglutination.

This characteristic explains why in scenarios where multiple antigenic determinants are present, such as in viral infections where a variety of epitopes are involved, relying solely on monoclonal antibodies might hinder the overall sensitivity and effectiveness of the assay. Thus, the restricted binding nature of monoclonal antibodies to one determinant makes them less versatile in hemagglutination contexts compared to polyclonal antibodies, which can recognize and bind to multiple epitopes on an antigen.