Calcium-loaded erythrocytes have a defect in complement regulation distinct from that resulting from exposure to 2-aminoethylisothiouronium bromide.
Calcium-loaded red blood cells (RBCs) previously have been shown to have an increased sensitivity to complement-mediated hemolysis and particularly to lysis mediated by the C5b-9 membrane attack complex (MAC) of complement. Because RBCs exposed to 2-aminoethylisothiouronium bromide (AET) also have been shown to be particularly sensitive to the MAC, a direct comparison of calcium-loaded and AET-treated RBCs was performed. Calcium-loaded and AET-treated RBCs shared a marked increase in sensitivity to lysis by the MAC in two different assays. However, measurements of C5b-7 and C9 binding suggested that different mechanisms were responsible. AET-treated RBCs showed an increase in C9 binding and an increased C9/C7 ratio consistent with functional loss of CD59/membrane inhibitor of reactive lysis (MIRL). In contrast, calcium-loaded RBCs had minimally increased C9 binding that resulted in C9/C7 ratios that were less than those for untreated RBCs, suggesting that CD59/MIRL inactivation had not occurred. When RBCs were incubated in acidified serum, AET-treated cells demonstrated a marked increase in C3b binding and hemolysis that was observed in neither control nor calcium-loaded RBCs. These results suggest that the underlying lesions responsible for an increase in susceptibility to complement-mediated hemolysis are different for calcium-loaded and AET-treated RBCs.
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Children's Hospital Oakland Research Institute, CA 94609, USA.
Mitsuyoshi
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D000328:Adult; D015703:Antigens, CD / Q000097:blood / Q000276:immunology; D018957:CD59 Antigens; D002118:Calcium / Q000097:blood / Q000494:pharmacology*; D003179:Complement C3b / Q000378:metabolism; D003182:Complement C5 / Q000378:metabolism; D050776:Complement C5b; D003184:Complement C7 / Q000378:metabolism; D003186:Complement C9 / Q000378:metabolism; D015938:Complement Membrane Attack Complex / Q000502:physiology; D003165:Complement System Proteins / Q000502:physiology*; D004912:Erythrocytes / Q000187:drug effects / Q000276:immunology*; D006461:Hemolysis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007074:Immunoglobulin G / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000097:blood / Q000276:immunology; D000338:beta-Aminoethyl Isothiourea / Q000494:pharmacology*
D015703:Antigens, CD; D018957:CD59 Antigens; D003182:Complement C5; D003184:Complement C7; D003186:Complement C9; D015938:Complement Membrane Attack Complex; D007074:Immunoglobulin G; D008562:Membrane Glycoproteins; D000338:beta-Aminoethyl Isothiourea; D003179:Complement C3b; D050776:Complement C5b; D003165:Complement System Proteins; D002118:Calcium