Quantitation of C3 subcomponents on red cells coated with complement in vitro

The quantification of C3 fragments on erythrocytes: estimation of C3 fragments on normal cells, acquired haemolytic anaemia cases and correlation with agglutination of sensitized cells

A sensitive method is described for the quantification of C3 fragments on erythrocytes. A radiolabelled monoclonal antibody, was used which was directed against a C3d determinant on all forms of cell bound C3. The number of C3 molecules on normal erythrocytes was estimated to be 420 +/- 140. The strength of the antiglobulin test increased from negative to 5+ over a range of only 850 C3 molecules (400-1250). A blood donor with a positive direct antiglobulin test was found to have 4800 molecules per cell whereas three cases of cold haemagglutinin disease with active haemolysis had from 16 000 to 52 020 C3 molecules per cell. This test has an application in the testing of acquired haemolytic anaemia cases with a positive direct antiglobulin test with C3 bound to the cells and in the standardization of sensitized cells used for testing antiglobulin reagents by various serological techniques.

Membrane-bound immunoglobulins and complement components on young and old red cells

In order to characterize changes in membrane-bound immunoglobulins and complement components, red cells (RBCs) were separated into young and old populations by simple centrifugation. Old RBCs had reduced mean corpuscular hemoglobin volume, increased mean corpuscular hemoglobin concentration, and reduced sialic acid. Using radioactive anti-antiglobulin techniques, old RBCs were shown to have more IgG, IgM, IgA, and C3d on their surfaces than did young RBCs; there was no increase on old RBCs of C3b, factor B, C4b, or C5. Similar results were observed with RBCs strongly coated with C3d in vivo from a patient with cold agglutinin disease. RBCs taken into ethylenediamine tetraacetate, washed thoroughly in saline, and then stored for prolonged periods in Alsever's solution or kept in autologous ethylenediamine tetraacetate plasma, at 4 degrees C, showed no increase in RBC-bound C3d with increased storage time. If, however, blood was taken into citrate-phosphate-dextrose and maintained at 4 degrees C in autologous plasma, a significant increase in RBC-bound C3d was observed in the mixed-cell population with prolonged storage time. Order donor blood units, taken into citrate-phosphate-dextrose and stored at 4 degrees C as packed red cells, showed higher levels of RBC-bound C3d in the mixed-cell population than did units stored for a shorter time. In no case did donor unit RBCs give a positive direct antiglobulin test on serologic testing with anti-C3d. The findings complement data already collected on membrane and cytoplasmic changes in aging RBCs and may contribute to an understanding of RBC senescence.

Measurement of fragments of the third component of human complement on erythrocytes by a new immunochemical method

This paper describes a new antiglobulin consumption method to quantitate the fragments of the third component of human complement (C3) on red blood cell (RBC) membranes. Zymosan-bound C3, which can be stored frozen at -80 degrees C for years, was used as a standard in these tests. Using anti-C3c antibody, zymosan-bound C3 could be calibrated against soluble converted C3 (beta 1A), but not against soluble, native C3 (beta 1C). Calibration with several commercial serum standards yielded virtually identical values. Approximately 79.8 +/- 28.2 C3d molecules (mean +/- 1 SD, n = 50) were detected on normal, freshly collected RBC by this method, whereas no C3c fragments were noted. EC43, prepared by dilution of blood samples with low ionic strength solution, had between 650 and 3,100 C3 molecules/RBC when measured with anti-C3c and between 1,140 and 6,500 C3 molecules when measured with anti-C3d. These data indicated that part of the C3b molecules on EC43 had cleaved to C3d. EC43 are reported to have up to 200,000 C3 molecules when measured by other techniques. To resolve this discrepancy, EC43 were prepared by dialysis of blood samples against low ionic strength solution. About 97.5% of C3 remained in plasma after dialysis supporting the results of our tests. The new assay is an accurate and sensitive method of quantitating C3 fragments bound to RBC in vivo and in vitro.

Complement in thrombotic thrombocytopenic purpura

This report describes a patient with recurrent thrombotic thrombocytopenic purpura (TTP) in whom complement activation was observed during the acute episodes. Serum C3, C4, and CH50 were reduced, and there was deposition of C3 on red cells and platelets. These findings returned to normal during clinical remission.