Human anti-phosphorylcholine antibodies share idiotopes and are self-binding

We have previously shown that BALB/c antipneumococcal polysaccharide antibodies with phosphorylcholine (PC) specificity are self-binding, mediated by hypervariable sequence structure of the heavy chain. We extended the observation of self-binding anti-PC antibodies to naturally occurring human anti-PC antibodies. Anti-PC antibodies were purified from normal donor sera and shown to bind to monoclonal antiidiotypic anti-T15 antibodies originally raised against the murine T15 idiotype. These human antibodies are self-binding which is inhibitable by the PC hapten and the murine T15 (50-73)-derived Vh peptide. The anti-PC antibodies were further separated into id-positive and id-negative anti-PC antibodies. Only the T15 id-positive preparation was self-binding. These findings demonstrate an evolutionary, conserved biological property between mouse and man associated with a naturally occurring antibacterial antibody. This conserved biological and structural property may have been selected in evolution because it is part of an important immune defense mechanism against bacterial and other environmental pathogens.