Quantification by ELISA of erythrocyte-bound C3 fragments expressing C3d and/or C3c epitopes in patients with factor I deficiency and with autoimmune diseases.
A sensitive ELISA assay for quantifying erythrocyte (E) bound C3 fragments was developed. The assay employs a double-antibody sandwich technique, using polyclonal anti-C3d or anti-C3c antibodies to quantify C3 fragments, expressing C3d and/or C3c epitopes in washed, detergent-solubilized E. The assay detected 50-120 molecules of C3d per E in healthy individuals. Antigens reacting with anti-C3c antibodies were also detected on E from normal individuals, but the density of C3c-epitopes was 0.9-2.4 times lower than that of C3d-epitopes. In 2 patients with congenital factor I deficiency significantly increased density of E-bound C3c- as well as C3d-antigen was observed. Plasma infusion in one of the patients induced a loss of E-bound C3c-antigens, indicating cleavage of E-bound C3b to iC3b and further to C3c and E-bound C3d. Loss of C3c-antigens also occurred following in vitro treatment with normal human serum of E from one of the patients. Two thirds of 22 patients with systemic lupus erythematosus (SLE) and of 18 patients with rheumatoid arthritis had significantly increased density of E-bound C3d, the highest density being 490 C3d molecules/E in an SLE patient. The density of E-bound C3d correlated with the plasma-C3d concentration, indicating that the coating of E with C3d reflects the degree of complement activation.
Møller Rasmussen
J
J
Institute of Medical Microbiology, Odense University, Denmark.
Jepsen
H H
HH
Teisner
B
B
Holmskov-Nielsen
U
U
Rasmussen
G G
GG
Svehag
S E
SE
D000347:Afibrinogenemia / Q000097:blood / Q000151:congenital / Q000276:immunology*; D000372:Agglutination Tests; D000818:Animals; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000276:immunology; D001327:Autoimmune Diseases / Q000097:blood / Q000276:immunology*; D003176:Complement C3 / Q000032:analysis*; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000276:immunology*; D004912:Erythrocytes / Q000276:immunology*; D005260:Female; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000097:blood / Q000276:immunology; D008297:Male; D011817:Rabbits
D003176:Complement C3; D000939:Epitopes