Circulating C4 levels in rats after IVIG treatment and subsequent injection of anti-Thy 1 MoAb. Sera of the rats used in the experiment described in Fig 5 were used for quantitation of circulating complement levels. The concentration of C4 was quantitated by rocket electrophoresis using a monospecific rabbit anti-rat C4 antiserum. The asterisk (*) indicates a significant reduction of C4 as compared with t = −30 minutes (Student’s t-test, P < .05). Columns are mean values of duplicate measurements with indication of the SD.