Direct Agglutination of Weak D Red Cells by Tetramolecular Complexes Containing Monoclonal IgG Anti-D

Abstract

The capacity of blood group antibodies to agglutinate red cells suspended in saline is largely dependent on the antibody isotype. The immunological cross- linking of IgG antibodies has previously been described as a means to increase the reactivity of IgG in many situations. We have prepared anti-D-containing complexes by blending a human IgG anti-D monoclonal antibody (mAb) and a murine anti-human IgG mAb. In standard red cell serology assays, the anti-D complexes exhibited a very high avidity and could agglutinate weak D-positive red cells in direct saline testing. These results indicate that potent saline hemagglutinating reagents of RhD and eventually of other blood group specificities can be prepared from IgG mAbs.

Tetramolecular immune complexes are more efficient than IVIg to prevent antibody‐dependent in vitro and in vivo phagocytosis of blood cells

“…Control experiments showed that the C5‐1 mAb could form agglutinating tetramolecular complexes with a human IgG anti‐D mAb (data not shown), as previously described for the 8D2‐8 murine anti‐human IgG mAb (Lemieux et al , 1993). To prepare the C5‐1/Fc tetramolecular complexes, purified C5‐1 antibodies and commercial human Fc fragments were mixed at different molar ratios and analyzed by gel filtration chromatography.…”

“…Tetramolecular IC are cross‐shaped structures that have been shown to form spontaneously by mixing equimolar amounts of rat anti‐mouse IgG mAbs and mouse IgG (Lansdorp et al , 1986). These complexes are widely used to isolate specific cells (Thomas & Lansdorp, 1988), and we previously showed that they could be useful for transforming IgG blood group antibodies into direct agglutinating reagents (Lemieux et al , 1993). Our results showed that tetramolecular IC containing human Fc fragments and mouse anti‐human IgG, are highly potent inhibitors of anti‐D‐mediated in vitro erythrophagocytosis, and that they also inhibit the clearance of antibody‐coated platelets in a mouse model of thrombocytopenia more efficiently than IVIg.…”