Which method applies antibody directly to the gel rather than placing it in a trough?

• A. Antibody is applied directly to the gel in immunofixation electrophoresis.
• B. Antibody is applied in a trough in immunofixation electrophoresis.
• C. Electrophoresis occurs before diffusion in immunofixation electrophoresis.
• D. Immunofixation electrophoresis does not use gels.

Answer: (A)

In immunofixation electrophoresis, the key idea is to visualize specific immunoglobulins by forming precipitin lines where antibody and antigen meet inside the gel. Placing the antibody directly on the gel puts it right at the location of the separated proteins, so it diffuses a short distance into the gel and binds specifically to the immunoglobulin bands. This produces crisp, well-defined lines corresponding to each immunoglobulin class or light chain.

If the antibody were placed in a trough, it would have to diffuse into the gel from the edge, which is slower and less localized, leading to broader or smeared lines. That trough diffusion approach is characteristic of traditional immunodiffusion rather than immunofixation electrophoresis.