What does the primary antibody influence most directly in immunohistochemistry?

• A. Sensitivity of detection system
• B. Specificity and avidity of staining
• C. Antigen preservation
• D. Detection color

Answer: (B)

In immunohistochemistry, the primary antibody directly determines what is labeled and how tightly that labeling occurs. This sets the staining pattern because the antibody’s specificity defines which antigen it will bind to, so only the intended target should be marked. The avidity, or overall binding strength between the antibody and its epitope, influences how strong the signal is where the antigen is present. Together, specificity and avidity shape both whether staining appears where it should and how intense that staining looks.

Other aspects of the assay—such as how bright the final color appears, or how sensitive the detection system is—depend more on components like the secondary antibody, amplification steps, and the chromogen used, rather than on the primary antibody itself. Antigen preservation is affected by tissue fixation and retrieval methods, which are separate from the antibody’s binding properties.