Non-precipitating guinea-pig antibodies as products of limited recognition of antigenic sites on the ovalbumin molecule.

The non-precipitating guinea-pig IgG1 and IgG2 antibodies, produced by administration of an excessive dose of hen ovalbumin (OA), were capable of forming only certain soluble complexes having molar ratios of antibody to antigen lower than 1-5:1, which were lower than the minimum ratio of 2-5:1 shown by anti-OA antibodies precipitable with OA. This unusual property of the non-precipitating antibodies was caused by a limited number of antibody molecules capable of binding to one OA molecule simultaneously, since the maximum number of their Fab' fragments binding to one OA molecule was only three and markedly less than the number (7-8) of Fab' fragments of the precipitating IgG1 and IgG2 anti-OA antibodies binding to one OA molecule. These results demonstrate that the non-precipitating IgG1 and IgG2 anti-OA antibodies are those reacting with some particular antigenic sites on OA, a number of the antigenic sites too few to permit insoluble lattice formation.