Practice question

When both antibody and antigen are soluble proteins, interaction can be visualized by allowing them to diffuse and form insoluble lattice in semi-solid medium. Immunoprecipitation encompasses methods where soluble immune complexes exceed solubility threshold and separate as precipitate, often facilitated by gel to stabilize band. Agglutination refers to particulate antigens like cells or latex beads, not soluble molecules. Radioimmunoassay employs radioactive labels for quantification, and flow cytometry measures cell surface fluorescence in suspension. Therefore detection of soluble-soluble reaction in gel, such as Ouchterlony, Mancini radial diffusion or immunoelectrophoresis, falls under precipitation category.