Monoclonal IgG and IgM Autoantibodies Obtained After Polyclonal Activation, Show Reactivities Similar to Those of Polyclonal Natural Autoantibodies

In this study, we described the properties of two groups of polyreactive IgG monoclonal antibodies (mAb) derived from splenocytes of a Plasmodium chabaudi-infected BALB/c mouse. These IgG mAb reacted with self antigens, but not with the parasite. Depending upon the antigen under study, they showed low (10(-5) M) to high (10(-8) M) affinities. When examined by immunoblotting using mouse organ extracts as the antigen source, each IgG mAb had a different reactivity profile. The IgG2b, but not the IgG2a mAb group, reacted with F(ab')2 fragments of IgG from normal mouse sera, as well as with F(ab')2 fragments of other mAb from the same fusion. Their anti-F(ab')2 activity was inhibited by various antigens, suggesting that the binding sites for these antigens and F(ab')2 fragments were close or overlapping. We also characterized two monoclonal IgM that were strongly and almost exclusively reactive with polyclonal F(ab')2 fragments of normal IgG, and that inhibited the binding of normal polyclonal IgG to self antigens. We previously described such properties for polyclonal IgM from normal mouse sera. The binding of the F(ab')2-reactive IgG mAb to self antigens was also inhibited by normal polyclonal IgM. These results indicate that the IgG and IgM obtained after polyclonal stimulation, exhibit characteristics similar to those of autoantibodies present in normal mouse sera. Furthermore, they confirm our previous studies showing the polyreactivity of polyclonal IgG. Finally, they also show that such IgG mAb exhibit properties similar to those of natural IgM, namely polyreactivity, affinity and connectivity.