A trypsin method for coating human red blood cells with plasma C3 and/or C4.

Simple procedures are described for the production of human red blood cells coated with C3 and/or C4 by brief trypsin treatment of cell-plasma mixtures at room temperature. These cells ('EC3/4'-try) were unusual in that their agglutinability by anticomplement sera, as compared to sucrose-water RBC, was similar when tested by AutoAnalyzer but was markedly reduced in manual testing, especially against anti-C4. In spite of this, both 'EC34'-try and 'EC3'-try were found to be suitable indicator cells for determining the adequacy of anti-C3c and/or anti-C3d activities in reagents used for manual antiglobulin tests.