Antiphospholipid antibodies from antiphospholipid syndrome patients activate endothelial cells in vitro and in vivo.
BACKGROUND
Antiphospholipid (aPL) antibodies are associated with thrombosis in patients diagnosed with antiphospholipid syndrome (APS) and enhance thrombus formation in vivo in mice, but the mechanism of thrombosis by aPL is not completely understood. Although aPL antibodies have been shown to inhibit protein C activation and activate endothelial cells (ECs) in vitro, no study has examined whether these antibodies activate ECs in vivo. Therefore, human affinity-purified aPL (ap aPL) antibodies from APS patients were tested in a mouse model of microcirculation using the cremaster muscle that allows direct microscopic examination of thrombus formation and adhesion of white blood cells (WBCs) to ECs as an indication of EC activation in vivo. Adhesion molecule expression on human umbilical vein endothelial cells (HUVECs) after aPL exposure was performed to confirm EC activation in vitro.


RESULTS
All 6 ap aPL antibodies significantly increased the expression of VCAM-1 (2.3- to 4.4-fold), with one of the antibodies also increasing the expression of E-selectin (1.6-fold) on HUVECs in vitro. In the in vivo experiments, each ap aPL antibody except for 1 preparation increased WBC sticking (mean number of WBCs ranged from 22.7 to 50.6) compared with control (14.4), which correlated with enhanced thrombus formation (mean thrombus size ranged from 1098 to 6476 versus 594 microm2 for control).


CONCLUSIONS
Activation of ECs by aPL antibodies in vivo may create a prothrombotic state on ECs, which may be the first pathophysiological event of thrombosis in APS.
Pierangeli
S S
SS
Department of Microbiology and Immunology, Antiphospholipid Standardization Laboratory, Morehouse School of Medicine, Atlanta, GA 30310-1495, USA. pierans@msm.edu
Colden-Stanfield
M
M
Liu
X
X
Barker
J H
JH
Anderson
G L
GL
Harris
E N
EN
D000328:Adult; D000818:Animals; D017152:Antibodies, Antiphospholipid / Q000276:immunology / Q000494:pharmacology*; D000918:Antibody Specificity; D016736:Antiphospholipid Syndrome / Q000276:immunology* / Q000503:physiopathology; D001327:Autoimmune Diseases / Q000276:immunology* / Q000503:physiopathology; D002448:Cell Adhesion; D002478:Cells, Cultured; D004306:Dose-Response Relationship, Immunologic; D019040:E-Selectin / Q000032:analysis; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D005260:Female; D006023:Glycoproteins / Q000276:immunology; D006801:Humans; D007116:Immunization, Passive; D007074:Immunoglobulin G / Q000494:pharmacology; D018799:Intercellular Adhesion Molecule-1 / Q000032:analysis; D016682:Lupus Coagulation Inhibitor / Q000276:immunology / Q000494:pharmacology; D008297:Male; D051379:Mice; D008833:Microcirculation / Q000187:drug effects; D019851:Thrombophilia / Q000209:etiology*; D013927:Thrombosis / Q000209:etiology; D019010:Vascular Cell Adhesion Molecule-1 / Q000032:analysis; D053482:beta 2-Glycoprotein I
D017152:Antibodies, Antiphospholipid; D019040:E-Selectin; D006023:Glycoproteins; D007074:Immunoglobulin G; D016682:Lupus Coagulation Inhibitor; D019010:Vascular Cell Adhesion Molecule-1; D053482:beta 2-Glycoprotein I; D018799:Intercellular Adhesion Molecule-1