Characterization of High-Affinity Anti-Fluorescyl IgM Antibodies

High-affinity IgM rabbit antibodies were elicited using the fluorescein hapten system. Purity and identification of IgM and IgG anti-fluorescyl antibodies was determined by immunoelectrophoresis and SDS-polyacrylamide gel electrophoresis. Ultracentrifugation studies verified that liganded antibodies were of a high mol. wt (901 kd). Comparative analyses of IgM and IgG anti-fluorescyl antibody active sites substantiated the observation that purified IgM preparations, similar to their IgG counterparts, possessed high-affinity antibody active sites. Dissociation rate data confirmed that some IgM molecules within the purified antibody populations possessed association constants at 10 super(11) M super(-1), comparable with values of 10 super(11) M super(-1) or greater obtained for some anti-fluorescein IgG populations studied in this laboratory, A diffusion-controlled association rate of 4.6 Chi 10 super(8) M1) sec super(-1) was assumed in dissociation rate calculations. This is the first report of purified IgM antibodies possessing exceptionally high affinities.