Disappearance of IgG2B autoantibodies associated with recovery from anaemia.

Mice immunized with cross-reacting rat erythrocytes develop autoimmune haemolytic anaemia as indicated by haematological data and erythrocyte autoantibodies. With continued immunization the mice recover haematologically but remain Coombs' positive. Coombs' tests were performed using monospecific antisera to determine whether the recovery from anaemia was associated with a change in the class or subclass of the autoantibodies produced. In both splenectomized mice and in unsplenectomized mice the following subclass of erythrocyte autoantibodies were present: IgG1, IgG2A, IgG2B. IgA autoantibodies were not detected and IgM autoantibodies were only detected in splenectomized mice 1-3 weeks after the IgG autoantibodies had appeared. After six immunizations the frequency of IgG2B autoantibodies decreased and by the tenth immunization and thereon, IgG2B autoantibodies were not detected. It is proposed from these results that the anaemia is caused by IgG2B autoantibodies and the the sudden exacerbation in the anaemia that occurs in splenectomized mice is due to the production of IgM autoantibodies.