Both IgG- and C1q-receptors play a role in the enhanced binding of IgG complexes to human mesangial cells.
The presence of immunoglobulin G (IgG) in the mesangial area in kidneys of patients with different forms of glomerulonephritis suggests a role for IgG in the inflammatory process. This study investigates whether IgG is able to bind to cultured human mesangial cells (MC) in vitro. Incubation of MC with 125I-aggregated IgG(125I-AIgG), as a model for immune complexes (IC), at 4 degrees C resulted in a time- and dose-dependent binding of 125I-AIgG to MC. The binding of 125I-AIgG to MC was inhibited by excess AIgG or Fc-fragments and not by F(ab')2-fragments or human serum albumin (HSA). Scatchard analysis revealed the presence of 2.8.10(6) receptors/cell with an affinity of 9.7.10(7) M-1. Incubation of MC with 125I-C1q resulted in a time- and dose-dependent binding of 125I-C1q to MC. The binding of 125I-C1q was inhibited by excess C1q or C1q talls and not by HSA. Scatchard analysis revealed the presence of 3.2.10(7) binding sites/cell with an affinity of 1.4.10(7) M-1. Immunoprecipitation of 125I-labeled MC membrane proteins with C1q or monoclonal antibodies directed against human C1q-R revealed a single 66 to 68 kd band under reducing conditions. Fluorescence-activated cell-sorter analysis revealed an average of 60.1% +/- 5.4% of the cells positive with a mean channel of fluorescence of 592. A cooperative effect between C1q-R and Fc gamma-R in the binding of 125I-AIgG to MC, was assessed by incubation of 125I-AIgG in the presence of increasing concentrations of C1q, C1q talls, or delta C1q. Only intact C1q showed a 6- to 11-fold enhancement in binding of 125I-AIgG to MC. These studies demonstrate the occurrence of C1q-R and Fc gamma-R on MC and indicate that binding of IC is enhanced after interaction of IC with C1q.
van den Dobbelsteen
M E
ME
Department of Nephrology, University Hospital Leiden, The Netherlands.
van der Woude
F J
FJ
Schroeijers
W E
WE
Klar-Mohamad
N
N
van Es
L A
LA
Daha
M R
MR
D000911:Antibodies, Monoclonal / Q000494:pharmacology; D000936:Antigen-Antibody Complex / Q000378:metabolism*; D001665:Binding Sites; D002352:Carrier Proteins; D002478:Cells, Cultured; D015922:Complement C1q / Q000276:immunology / Q000378:metabolism; D005920:Glomerular Mesangium / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D018960:Hyaluronan Receptors; D007074:Immunoglobulin G / Q000276:immunology / Q000378:metabolism*; D007456:Iodine Isotopes; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D011233:Precipitin Tests; D011485:Protein Binding; D011951:Receptors, Complement / Q000276:immunology / Q000378:metabolism*; D017452:Receptors, IgG / Q000276:immunology / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; C087299:C1QBP protein, human; D002352:Carrier Proteins; D018960:Hyaluronan Receptors; D007074:Immunoglobulin G; D007456:Iodine Isotopes; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D011951:Receptors, Complement; D017452:Receptors, IgG; C032402:complement 1q receptor; D015922:Complement C1q