Assessment of Complement Binding by Anti-D and Anti-M Antibodies Employing Labelled Antiglobulin Antibodies

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Abstract
The presence of small amounts of C3d [d fragment of complement component 3] on freshly obtained normal [human] red blood cells (RBC) was demonstrated by a radio-labeled antiglobulin technique; this increased 1.5-fold after incubation in fresh normal serum. No significant further increase in bound C3d was demonstrated for cDE/cDE, CDe/CDe, -D-/-D- RBC maximally sensitized with any of 3 potent anti-D antibodies. When anti-c, anti-D and anti-E antibodies were used in combination to sensitize cDE/cDE RBC, bound C3d increased by approximately 22%; a similar increase occurred with cde/cde RBC and was considered non-Rh specific. Umbilical cord RBC from 4 infants severely affected by anti-D hemolytic disease of the newborn did not exhibit more bound C3d than cord RBC from normal controls. One serum containing Ig[immunoglobulin]M anti-M bound a small amount of complement in vitro; 2 IgG anti-M sera did not.