PARADOXICAL BEHAVIOR OF ASYMMETRIC IGG ANTIBODIES

Changes in the quantity and quality of antibodies occur in the course of an immune response. This review describes the physicochemical and b iological properties of asymmetric antibodies as well as their functio ns, beneficial or harmful to the host, according to the nature of the antigen and the particular situation in which they act. Asymmetric ant ibodies have two paratopes, one of high affinity, with K-0 similar to that of symmetric antibodies, and the other one with an affinity for t he antigen 100 times lower. Functional univalence is due to steric hin drance present in one of the paratopes by the carbohydrate moiety atta ched to the Fd fragment of the Fab region, so these antibodies are una ble to form large antibody-antigen complexes and cannot trigger reacti ons, such as complement fixation, phagocytic activity and antigen clea rance. When asymmetric IgG antibodies are specific for self-antigens, they prove beneficial for the host by exerting regulatory functions. I n allergic manifestations, in autoimmune diseases and especially durin g pregnancy despite the fact that the antigens responsible for the pro cess are foreign to the host, they also perform beneficial activity. D uring pregnancy, the placenta secretes molecules or factors that regul ate the synthesis of these antibodies, thus favoring fetal protection.