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The authors studied and compared the complement-fixing activity of model immune complexes with different molecular mass. The complement-fixing activity of the complexes was found to be linearly independent of the molecular mass, being mainly determined by the size of the complex, and to be slightly dependent on the concentration of aggregated immunoglobulins. As far as the aggregates with a molecular mass over 20 IgG are concerned, addition of complement leads to the dissociation of the complexes.

Specific complex formation by human immunoglobulins of classes M, G, and A with antibodies against class G immunoglobulins was studied by a thermistographic method. Depending on the type of interacting immunoglobulins, the rate and intensity of the process were shown to differ and to be maximal for IgM. Depending on the character of the curves obtained the class of immunoglobulins being synthesized at that given moment could be determined. Disturbance of the internal structure of the macromolecules of the immunoglobulins, as a result of heating, for example, leads to changes in the mechanism of complex formation; the important question in this event is which of the interacting components undergoes denaturation.