Which technique combines electrophoresis with immunodiffusion to identify antibodies?

• A. Immunodiffusion
• B. Radial immunodiffusion
• C. Ouchterlony diffusion
• D. Immunoelectrophoresis

Answer: (D)

This tests the idea of using an electric field to separate proteins first, then applying antibody-based detection. Immunoelectrophoresis starts by running serum proteins through a gel under an electric field, separating them by size and charge. After the separation, antibodies are introduced so they diffuse toward the resolved proteins. Where a specific antibody meets its antigen, a precipitin reaction occurs, creating a visible arc or band that identifies the presence of that antibody. This combination—electrophoretic separation followed by immunodiffusion—is what makes immunoelectrophoresis the technique in question. The other methods rely solely on diffusion without any prior electric separation, so they don’t combine both steps.