Evaluation of heat-damaged and IgG-coated red cells for testing reticuloendothelial function

In vitro methods for standardising and assessing the reproducibility of reticuloendothelial function tests in man were performed. Variation in the degree of heat-induced red blood cell damage could be detected by both Channelyzer plots and a filtration test of red cell plasticity although the former test was less sensitive and difficult to quantitate. In a consecutive study of the clearance of heat-damaged red blood cells (HDRBC) in 8 patients and 2 normal individuals, consistent changes were demonstrated by both assays although occasionally one assay alone provided inconclusive results. When undamaged red cells were coated with IgG anti-D antibodies, the number of IgG molecules bound per red cell was determined by an indirect antiglobulin radioimmunoassay. With this assay, it was shown that the rate of clearance of coated cells was related to the amount of cell bound IgG anti-D. Some variation in the degree of coating of cells from patients with systemic lupus erythematosus was found although the differences were insufficient to account for the reported reduction in the clearance of IgG-coated cells in patients with this disease. The radioimmunoassay and microhaemagglutination techniques revealed that neither IgG, Clq, C3 or C3d were bound to HDRBC following incubation in autologous serum suggesting that these cells were cleared in vivo by mechanisms unrelated to immune receptor recognition.