Studies on the biological functions of monoclonal immunoglobulins and their fragments.

Complement-binding ability of three isolated monoclonal proteins of IgG class, their Fab, and Fc fragments was analyzed (including tests for the presence of polymers, aggregated forms and immune complexes), and the influence of two monoclonal IgG lambda proteins on fibrinogen conversion to fibrin was determined. Two proteins--IgG1 lambda and IgG3K--bound small amounts of complement only when tested in native form, but failed to bind complement after thermal aggregation. Papain-digestion of these proteins revealed a significant ability of complement binding by Fc fragments. The third protein--M-IgG1 lambda--bound large amounts of complement when used in its native form, but after thermal aggregation this ability decreased. This protein differs in structure from monoclonal Ig described here. It was shown by the atypical elution pattern of papain digest of M-IgG1 lambda from CM-cellulose and by the anticoagulative activity of this protein. In control tests with polyclonal immunoglobulin complement-binding ability increased after thermal aggregation of the immunoglobulin, Fc fragments of the polyclonal immunoglobulin bound lower amounts of complement than whole molecules. As already mentioned, the activity of the factor inhibiting fibrinogen-to-fibrin conversion was observed in only one of two tested proteins M-IgG lambda. This activity was not connected selectively with Fab fragment. In identical concentrations polyclonal IgG had no effect on fibrinogen-to-fibrin conversion.