When soluble antigens diffuse in a gel that contains antibody, in which zone does optimum precipitation occur?

When soluble antigens diffuse in a gel that contains antibody, in which zone does optimum precipitation occur?

• A. Prozone
• B. Zone of equivalence
• C. Postzone
• D. Prezone

Answer: (B)

In this diffusion setup, precipitation is best when antigen and antibody meet in equivalent concentrations so that many binding sites can cross-link and form a continuous lattice. This balance, the zone of equivalence, allows enough cross-linking between multiple antigen and antibody molecules to create an visible precipitin network. If antibody is in excess (prozone), each antigen tends to be fully occupied by antibodies without linking to other antigens, preventing lattice formation. If antigen is in excess (postzone), there aren’t enough antibodies to bridge multiple antigens, so precipitation also fails to form.

In this diffusion setup, precipitation is best when antigen and antibody meet in equivalent concentrations so that many binding sites can cross-link and form a continuous lattice. This balance, the zone of equivalence, allows enough cross-linking between multiple antigen and antibody molecules to create an visible precipitin network. If antibody is in excess (prozone), each antigen tends to be fully occupied by antibodies without linking to other antigens, preventing lattice formation. If antigen is in excess (postzone), there aren’t enough antibodies to bridge multiple antigens, so precipitation also fails to form.