Determination of serum immunoglobulin levels in NZB and normal mice has indicated that an elevation of the γM-globulin level occurs in NZB mice. This can be demonstrated in young NZB mice well before other autoimmune manifestations are observed. A slight elevation of γM-globulin was also observed in NZB hybrid mice.

Erythrocyte autoantibodies were analyzed by the direct Coombs' test with specific antiimmunoglobulin reagents. Autoantibodies in NZB mice can be of all immunoglobulin classes, although predominantly of γG1-class. In (NZB x NZC)F1 hybrid mice, although Coombs' positivity develops around the same age as in NZB mice, there is a greater restriction of the autoantibodies into γM- and γG1-classes.

Preliminary attempts to quantitate immunoglobulins coating NZB red cells have shown that there are approximately 400 molecules of γM and 5000 molecules of γG-globulin per NZB mouse red cell.

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