ABSTRACT
Immunogens have more than one antigenic determinant per molecule (i.e., are multi-determinant). Immunization with antigen therefore results in many antibody populations, 92each directed toward different determinants on the protein. Since one molecule of Ab (IgG) can react with two molecules of Ag, and one molecule of Ag can react with many molecules of Ab, a lattice or framework consisting of alternating molecules of Ag and Ab can be produced that precipitates. The extent to which a lattice forms depends on the relative amounts of Ag and Ab present (Figure 1). As the amount of Ag added increases, the amount of precipitate and Ab in the precipitate increases, until a maximum is reached, and then decreases with further addition of Ag. When there is both sufficient Ag and sufficient Ab, the combination of Ag and Ab proceeds until large aggregates are formed, which are insoluble and precipitate (equivalence). However, in Ab excess or in Ag excess, less lattice formation occurs and more soluble complexes are formed.
