What is the principle of the Western blot test and what does it detect?

• A. It detects nucleic acids after gel electrophoresis.
• B. It detects antibodies in serum using flow cytometry.
• C. It detects specific proteins separated by gel electrophoresis; in serology, it detects antibodies against those proteins.
• D. It detects viral particles in plasma.

Answer: (C)

Western blot combines separating proteins by size with antibody-based detection. Proteins are first separated on a gel, then transferred to a membrane. The membrane is exposed to a sample such as patient serum; if there are antibodies against the separated proteins, they bind to the corresponding bands. A labeled secondary antibody reveals these bindings, producing a banding pattern that shows which proteins elicit an antibody response. This means the test detects the specific proteins themselves, and in serology it detects antibodies in the serum that target those proteins. It’s a two-step process: protein separation by gel electrophoresis followed by immunodetection. This is why it’s not about nucleic acids, flow cytometry, or directly detecting viral particles in plasma.