Antibodies with multiple binding functions. Induction of single immunoglobin species by structurally dissimilar haptens.

Anti-hapten sera prepared in rabbits contain individual immunoglobulin species capable of binding several pairs of structurally diverse haptens A and B. (A = inosine, uridine, menadione, vitamin K(1), ribonuclease; B = 2,4-dinitrophenyl). In antisera against hapten A subjected to isoelectric focusing, there are many anti-A immunoglobulin species, but only a small proportion of these bind both A and B. When rabbits are primed with haptens A coupled to a carrier and then challenged with hapten B-carrier complex, there is an early restricted response of those species that bind both A and B. Later, immunoglobulins appear which bind B, but not A. These results suggest that multiple-binding antibodies exist in antisera against hapten and that such multiple binding is functional; i.e., that when two diverse haptens A and B bind to an immunoglobulin, both haptens may stimulate the cell-surface receptor to induce production of this immunoglobulin. Such phenomena may also provide a molecular basis for maturation of the immune response.