Complement - fixation in the interaction of normal rabbit gamma G' globulin and its Fab' fragment

Complement consumption induced by Fab' fragments of rabbit IgG, irrespectively of their state of aggregation, requires the presence of homologous rabbit IgG. Up to a certain concentration of Fab' fragment, the amount of complement fixed is a linear function of the Fab' fragment dose, but further raising of the Fab'-fragment concentration does not result in complete complement consumption in the sample. The interaction between Fab' fragment and IgG is not strictly species specific.