Internalization of antibodies by endothelial cells via fibronectin implicating a novel mechanism in lupus nephritis.
BACKGROUND
One of the crucial events in lupus nephritis is the glomerular deposition of immunoglobulins (Igs), of which pathogenic properties have been proposed mostly to be either type IIor type III allergic reactions. Some of IgG3-producing hybridoma clones established from an MRL/MpTn-gld/gld (MRL/gld) lupus mouse generate wire loop-like lesions in glomeruli resembling lupus nephritis when injected into SCID mice. These clones are useful for analyzing the mechanisms of glomerular deposition of antibodies in lupus nephritis at the monoclonal level.


METHODS
Glomerular lesions of SCID mice injected with the hybridoma clones, 17H8a or 1G3 as control were analyzed by light and electron microscopy. Interaction of the antibodies with human glomerular endothelial cells (HGECs) and human umbilical vein endothelial cells (HUVECs) in vitro was studied by fluorescence microscopy, electron microscopy, and flow cytometry.


RESULTS
Both antibodies did not show any antigen specificity for mouse glomeruli. The glomerular lesions generated by 17H8a, but not by 1G3, contained electron-dense deposits not only in subendothelial regions but also in the cytoplasm of endothelial cells, suggesting internalization of the 17H8a antibodies by endothelial cells. In cell culture studies, internalization of only 17H8a antibodies by HGECs and HUVECs was observed, but the antibodies did not have antigen specificity for both types of endothelial cells. The internalization by HUVECs was mediated by actin polymerization, and it was inhibited by RGDS (Arg-Gly-Asp-Ser) tetrapeptide, antihuman fibronectin and antihuman integrin beta1 monoclonal antibodies.


CONCLUSIONS
The interaction between particular antibodies and endothelial cell surface integrins via fibronectin may be involved in their subsequent internalization by endothelial cells leading to antibody deposition in glomeruli. This may be one of the mechanisms of glomerular injury in lupus nephritis.
Fujii
Hiroshi
H
Department of Pathology, Ehime University School of Medicine, Ehime, Japan.
Nakatani
Kimihiko
K
Arita
Norimasa
N
Ito
Mitsuko R
MR
Terada
Miho
M
Miyazaki
Tatsuhiko
T
Yoshida
Minako
M
Ono
Masao
M
Fujiwara
Takashi
T
Saiga
Kan
K
Ota
Toshiyuki
T
Ohtani
Haruo
H
Lockwood
Martin
M
Sasaki
Takeshi
T
Nose
Masato
M
D000818:Animals; D000911:Antibodies, Monoclonal / Q000493:pharmacokinetics*; D042783:Endothelial Cells / Q000276:immunology / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology; D005353:Fibronectins / Q000378:metabolism*; D006825:Hybridomas; D007678:Kidney Glomerulus / Q000166:cytology; D008181:Lupus Nephritis / Q000276:immunology* / Q000378:metabolism*; D051379:Mice; D019463:Mice, Inbred MRL lpr; D016513:Mice, SCID; D011485:Protein Binding / Q000276:immunology; D014471:Umbilical Veins / Q000166:cytology
D000911:Antibodies, Monoclonal; D005353:Fibronectins