T15 PC-binding monoclonal antibodies retain specificity when they switch from IgM to IgG

The expression of some Ag-binding sites and their associated H and L chain V region genes are often dominated by one or another of the IgG subclasses. This is true of T15 anti-phosphorylcholine (PC) response in which the dominant T15 H (V1, DFL11.6 JH1) and L (VK22, JK5) chain V regions are seldom found associated with the gamma 2b or gamma 2a C regions in the circulation of BALB/c mice. In the present study we describe the characterization of gamma 2b, gamma 2a, and gamma 1 anti-PC antibodies obtained from IgM-producing hybridomas by Ig switching in culture. All switch variants retained the parental T15 idiotype, PC binding, and fine specificity. We thus conclude that the apparent in vivo restriction on the expressed T15 PC binding gamma 2 antibodies is not due to a conformational limitation on the expression of the anti-PC T15 binding site. Further, these studies confirm that in vitro switching can be used to generate mAb that are not readily available in vivo.