ABSTRACT
As a consequence of antigen-antibody reactions, important changes occur in the physical state of the antibodies. As antigen and antibodies react and form aggregates, the antibody molecules undergo conformational changes. These events are responsible for changes in the spatial orientation and exposure of biologically active domains or segments located on the Fc region of those antibodies. For example, the Fc region of antigen-bound molecules of IgM, IgG3, IgG1, and to a lesser degree IgG2, are able to bind and activate the first component of a series of rapidly acting plasma proteins, known as the complement system.
