Effects of pH or ionic strength on the reactivities of mono- and polyspecific IgG antibodies.

The reactivities of mono- and polyspecific mouse monoclonal antibodies (mAb) were compared by ELISA using immobilized antigens under different conditions, varying the pH or the NaCl concentration. The monospecific group was composed of 6 IgG directed against Staphylococcus aureus capsular polysaccharides and of 3 IgG specific to actin, myosin or tubulin. These antibodies were compared with 6 polyreactive mAb also of the IgG isotype. Marked differences were noted between the reactivities of the mono- and polyreactive IgG. pH variations had little or no effect on the reactivity of monospecific mAb to polysaccharides or to proteins. In contrast, the binding of polyreactive mAb was dependent on the pH, and the profile differed for each antigen. The NaCl concentration had opposite effects on mono- and polyreactive mAb: the binding of almost all the monoreactive mAb was increased at high NaCl concentration, while it was decreased for polyreactive mAb. In contrast, the effects of varying the pH or ionic strength on the coated antigens were negligible. The variation coefficients calculated for the pH and NaCl concentration were higher for the polyreactive mAb under study, which seems to indicate that electrostatic interactions and charged residues might be more important for these mAb than for the monoreactive ones. This characteristic might be one explanation for the particular properties of these polyreactive antibodies.