Serum-serum interactions in autoimmune mice.

Sera from a majority of old, sick mice of the MRL/l strain interact with other MRL/l sera to form visible immunoprecipitates and fix complement. The mouse sera can be divided into two sets such that interset interactions are far more common than intraset ones. The reactive principle in each mouse serum is IgG in the form of an intermediate-sized complex. Reactivity between sera is dependent on IgG anti-IgG specificities.