Beta-2-glycoprotein specificity of human anti-phospholipid antibody resides on the light chain: a novel mechanism for acquisition of cross-reactivity by an autoantibody.
We have recently shown that the anti-cardiolipin activity of human anti-phospholipid antibody UK4 (lambda) resides on its heavy chain. We now show that UK4 possesses strong reactivity to the plasma-protein beta2-Glycoprotein I (beta2-GPI) also. Utilizing chain shuffling experiments involving an unrelated anti-p185 antibody 4D5 (kappa) with no reactivity to beta2-GPI, we now demonstrate that both the constructs possessing the auto-antibody-derived light chain exhibited significant binding to beta2-GPI. However, the construct possessing UK4 heavy chain in association with 4D5 light chain, exhibited no anti-beta2-GPI activity. Furthermore, there was a low increase (approximately 10%) in the binding of UK4 to cardiolipin in the presence of beta2-GPI. The results demonstrate that anti-beta2-GPI activity resides on UK4 light chain and, importantly, this activity could be transferred to a novel antibody construct via the light chain alone. Computer-generated models of the three-dimensional structures of UK4 and its hybrids, suggest predominant interaction of UK4 light chain with domain IV of beta2-GPI. Molecular docking experiments highlight a number of potential sites on beta2-GPI for interaction of UK4 and indicate as to how beta2-GPI recognition may occur primarily via the autoantibody light chain. The study provides first demonstration of the occurrence of anti-phospholipid and anti-beta2-GPI activities separately on heavy and light chains of an autoantibody. The possible mechanisms that such antibodies may employ to recognise their antigens, are discussed.
Department of Medicine, Centre for Rheumatology, Bloomsbury Rheumatology Unit, University College London Hospital, Arthur Stanley House, 40-50 Tottenham Street, London W1P 9PG, UK. sanjeev.kumar@antisoma.com
Sanjeev
S
Kumar
Sylvia
S
Nagl
Jatinderpal K
JK
Kalsi
Chelliah T
CT
Ravirajan
Dee
D
Athwal
David S
DS
Latchman
Laurence H
LH
Pearl
David A
DA
Isenberg
D017152:Antibodies, Antiphospholipid / Q000276:immunology*; D000918:Antibody Specificity; D001323:Autoantibodies / Q000276:immunology*; D001665:Binding Sites; D003001:Cloning, Molecular; D003429:Cross Reactions / Q000276:immunology*; D006023:Glycoproteins / Q000276:immunology*; D006801:Humans; D007147:Immunoglobulin Light Chains / Q000276:immunology; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D015202:Protein Engineering; D053482:beta 2-Glycoprotein I
D017152:Antibodies, Antiphospholipid; D001323:Autoantibodies; D006023:Glycoproteins; D007147:Immunoglobulin Light Chains; D053482:beta 2-Glycoprotein I