Immune complex binding to erythrocyte-CR1 (CD 35), CR1 expression and levels of erythrocyte-fixed C3 fragments in SLE outpatients.
Erythrocytes (E) from a cross-sectional group of 22 outpatients with systemic lupus erythematosus (SLE) and/or mixed connective tissue disease (MCTD), the majority without active disease (n = 14), were analyzed for CR1 antigen expression and capacity to bind complement opsonized, radiolabelled immune complexes (IC). Furthermore, E-bound C3 fragments and the plasma C3d concentration were determined. E-bound C3b/iC3b fragments were not elevated in patients with SLE, whereas E from 11 out of 22 SLE patients had increased C3d levels which correlated with the plasma C3d concentration (Rs 0.73, p less than 0.001). E-fixed C3d fragments did not affect the binding of Mab or preopsonized IC to E-CR1 and were not correlated with disease activity or medical treatment. Antigen expression of E-CR1 measured by ELISA or agglutination showed positive correlation with the IC binding capacity of E-CR1 (Rs 0.92 and 0.72 respectively, p less than 001). The IC binding capacity of E-CR1 from SLE patients was significantly reduced (p less than 0.005), whereas the antigen expression of CR1 (ELISA) on E from the patients did not differ from that of E from healthy donors (p greater than 0.1). E-CR1 antigen was measured by Mab reacting with an epitope outside the IC-binding site of E-CR1. E-CR1 antigen expression or IC binding showed no correlation either with disease activity or prednisolone treatment. However, 4 og 5 patients with MCTD and 4 of 5 patients receiving Imurel were found to have low E-CR1 expression and capacity to bind IC. Thus, measurement of antigenic E-CR1 in a cross-sectional group of SLE outpatients by use of Mab reacting with an epitope outside the ligand-binding region of CR1 did not reveal a significantly reduced CR1 expression. However, an assay for CR1-mediated IC binding showed a clearly reduced E-CR1 function.
Jepsen
H H
HH
Institute of Medical Microbiology, Odense University, Denmark.
Møller Rasmussen
J
J
Teisner
B
B
Schrøder
L
L
Holmskov
U
U
Jarlbaek
L
L
Isager
H
H
Svehag
S E
SE
D000936:Antigen-Antibody Complex / Q000032:analysis*; D015703:Antigens, CD / Q000032:analysis*; D003176:Complement C3 / Q000032:analysis / Q000276:immunology*; D004912:Erythrocytes / Q000276:immunology*; D006384:Hemagglutination; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000097:blood* / Q000276:immunology; D010045:Outpatients; D011951:Receptors, Complement / Q000032:analysis*; D017463:Receptors, Complement 3b
D000936:Antigen-Antibody Complex; D015703:Antigens, CD; D003176:Complement C3; D011951:Receptors, Complement; D017463:Receptors, Complement 3b