LUPUS ANTICOAGULANT ANTIBODY TO F1 REGION OF PROTHROMBIN

Abstract: Isolated antibodies directed against the F1 region of prothrombin, which antibodies mimic the effect of a lupus anticoagulant (LA) in vitro, and uses of the antibodies in blood clotting tests.

Description: LUPUS ANTICOAGULANT ANTIBODY TO FI REGION OF PROTHROMBIN Technical Field The present invention relates to reagents applicable for use in blood coagulation assays, particularly mimics of lupus anticoagulants. Background Art Lupus anticoagulants (LA) are regarded as phospholipid-interfering antibodies, somehow related to anticardiolipin antibodies detectable in many patients with systemic lupus erythematosus (SLE) and anti-phospholipid syndrome [lj . The LA are not directed at phospholipids er se, but rather at epitopes of protein complexes which contain specific phospholipids. In recent years there has been increasing evidence that these epitopes are contained on either beta-2 glycoprotein 1 or prothrombin. The subtype of LA acting through beta-2-glycoprotein 1 enhance the anticoagulant effect of this normally mild coagulation inhibitor and may increase its affinity for phospholipid. These LA are associated with phospholipid liposomes and may be detected by solid phase immunoassays. This class of LA is believed to be more readily detectable with the dilute Russell's viper venom time (DRWT) test whereas those LA that function through prothrombin are said to have more effect on the kaolin clotting time (KCT) [2]. The prothrombin-dependent LA do not sediment with phospholipid liposomes and may not pose such a significant prothrombotic risk as LA acting through beta-2-glycoprotein 1. Antibodies against prothrombin have been reported in many cases of LA, however, the association between prothrombin and these antibodies cannot usually be demonstrated n vitro [3]. In severe cases, low levels of prothrombin develop because complexes formed in vivo are cleared from circulation. Such patients have an increased risk of bleeding and some studies have suggested that plasmas containing LA often contain antibodies recognising the F1.2 part of the prothrombin molecule [4] , Other reports have shown that enzyme linked immunosorbant assays (ELISAs) for Fl.2 are not particularly sensitive to thrombotic risk in patients with lupus anticoagulants [5]. A variety of artificial standards for LA have been proposed for laboratory use. These have included phospholipases, annexins. polymyxin, quaternary ammonium detergents and monoclonal antibodies against beta-2- glycoprotein 1 [6] . None of these have been found to affect various clotting tests in the same pattern as typical LA. Although such agents show correction on addition of phospholipid similar to true LA, all except for monoclonal antibodies against beta-2-glycoprotein, the agents also show "correction" on mixing with normal plasma. The present inventor has now produced antibodies that act similarly to LA found in patients with clotting abnormalities. These antibodies in plasma act similarly to LA in not being corrected by the addition of normal plasma in blood clotting tests. The antibodies' actions in vitro are reversed by the addition of additional phospholipids to clotting tests, which is also observed with LA [7]. The present invention also serves as a model for other potential interferences of autoimmune antibodies on activation peptides, in particular those from components of the protein C pathway. Disclosure of Invention In a first aspect, the present invention consists in an isolated antibody directed against the Fl region of prothrombin, which antibody mimics the effect of a lupus anticoagulant (LA) in vitro. Preferably, the antibody is a monoclonal antibody. In a preferred embodiment, the monoclonal antibody is obtained from a mouse following immunisation with human prothrombin. preferably N- terminal peptides derived from human prothrombin. In obtaining suitable monoclonal antibodies, it is important to select clones producing antibodies directed to the Fl region of prothrombin. Suitable clones are usually selected by the ability of the antibody to bind Fl.2 but not F2 region of prothrombin. Screening of clones is usually carried out using Fl.2 coated wells of microtitre plates and testing for antibodies which bind thereto. Peptides including the amino acid sequence: Cys-Gly-Ser-Asp-Arg-Ala-Ile- Glu-Gly-Arg (SEQ ID NO: 1) (Glyl47 to Argl55 of prothrombin) have been found to be useful to immunise animals to obtain suitable monoclonal antibodies. It would be expected by persons skilled in the art from the present disclosure and teaching that other suitable antibodies can be generated which act similarly to the antibody examples described herein. Preferably, the monoclonal antibody is selected from 195/097a, 195/016. or 195/0155. More preferably, the antibody is 195/097a. The preferred antibody according to the first aspect of the present invention (195/097a) will be available commercially or by request from the applicant Gradipore Limited at PO Box 1865. Macquarie Centre, New South Wales. 2113 Australia. The antibodies can be generated using standard monoclonal antibody production techniques following appropriate immunisation of an animal, preferably a mouse. In a second aspect, the present invention consists in use of an isolated antibody according to the first aspect of the present invention in an n vitro blood coagulation assay. Preferably, the assay is an activated partial thromboplastin time (APTT) test using a reagent sensitive to LA. Other screening tests are also suitable and include kaolin clotting time (KCT), tissue thromboplastin inhibition test (TTIT), dilute Russell's viper venom time (DRWT), Taipan venom, and Textarin test. The antibodies according to the present invention are particularly suitable as mimics of naturally occurring LA. The present inventors have found that antibody concentrations of about 0.01 to 10 μmol are suitable for many common blood clotting tests. A concentration of up to about 0.7 μmol has been found to be maximally effective in some tests. This concentration is approximately half the level of prothrombin in normal plasma. It will be appreciated, however, that the concentration of antibody will vary depending on the test and particular use. In a third aspect, the present invention consists in a blood clotting test standard, the standard comprising plasma treated or mixed with the antibody according to the first aspect of the present invention. The standard is useful as a defined strength of lupus anticoagulant for control in clotting tests. The standard can be prepared by "spiking" normal human plasma with a defined amount of antibody and used to define the sensitivity of various clotting tests to LA. The standard is particularly suitable for tests including activated partial thromboplastin time (APTT) test, kaolin clotting time (KCT), tissue thromboplastin inhibition test (TTIT). dilute Russell's viper venom time (DRWT). Taipaan venom and Textarin test. In a fourth aspect, the present invention consists in a method of obtaining an antibody according to the first aspect of the present invention, the method comprising: (a) immunising an animal with prothrombin or a N-terminal peptide derived from human prothrombin: (b) testing for the production of an antibody in the animal which is capable of binding Fl.2 region of prothrombin but not capable of binding F2 region of prothrombin; and (c) isolating the antibody. Preferably the animal is a mouse which is immunised with a peptide including the amino acid sequence Cys-Gly-Ser-Asp-Arg-Ala-Ile-Glu-Gly-Arg (SEQ ID NO: 1). Preferably the antibody is a monoclonal antibody. Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. In order that the present invention may be more clearly understood, preferred forms will be described with reference to the following examples and drawings. Brief Description of Drawings Figure 1 shows the effect of different monoclonal antibodies on an APTT test. Figure 2 shows the effect of monoclonal antibodies against Fl on various blood clotting tests used for diagnosing LA. Figure 3 shows a comparison of monoclonal antibodies with LA on an APTT test. Modes for Carrying Out the Invention METHODS Monoclonal Antibody Production Monoclonal antibodies were produced by standard techniques [9] after immunising mice with whole prothrombin or peptides derived from human prothrombin. APTT Assay Standard assay techniques were used [10, 11]. RESULTS The monoclonal antibodies of importance were generated by immunising mice with whole human prothrombin and then selecting clones which specifically bound to the Fl region. Other antibodies were generated by immunising mice with the C-terminal peptide of F + 2 fragment (Sequence: Cys-Gly-Ser-Asp-Arg-Ala-Ile-Glu-Gly-Arg; which are amino acids Glyl47 to Argl55 of prothrombin) attached to ovalbumin. The amino acid sequence has been used previously to generate anti-Fl+2 antibodies [8], Surprisingly, it has been found by the present inventor that antibodies generated had lupus anticoagulant-like activity, a property which until now has been addressed to proteins binding to phospholipids. Interestingly. Fl + 2 is the inactive part of prothrombin after activation by prothrombin activators including the factor Xa/Va complex. The monoclonal antibodies were generated in order to replace monospecific polyclonal antibodies (rabbit) which are not easy to produce by standard monoclonal techniques and which have very low activity in clotting tests. Monoclonal antibodies directed against the Fl and Fl + 2 parts of prothrombin were found to prolong all the clotting tests normally used for detecting lupus anticoagulants (LA) such as the APTT (see Figure 1), KCT, DRWT. and TTIT. The strength of their effect on various clotting tests was in similar proportion as the sensitivity of these tests for typical LA (Figures 2 and 3). Phospholipids used for reversing the effect of LA in the DRWT also reversed the anticoagulant effect of these antibodies. This is apparent from Figure 2 where plasma containing the anti-FII-Fl monoclonal gave prolonged results with DRWT reagent but not with the DRWT (high phospholipid). Thus such MCA against Fl and Fl + 2 fulfil the current criteria for LA and might be useful as known standards of LA potency. The functional similarity of the antibodies to LA strongly suggests that the majority of LA may also be directed at complex epitopes involving the Fl or Fl + 2 regions of prothrombin. One of the monoclonal antibodies (92-195/097a, Figure 1) showed a typical lupus "cofactor" mixing pattern suggesting that subtle differences in Fl epitope may account for this phenomenon without any need for a separate cofactor. It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. REFERENCES 1. Brandt JT, Triplett DA, Alving B, Scharrer I. Thombosis and Haemostasis 1995 : 74; 1185-190. 2. Galli M, Finazzi G, Bevers EM, Barbui T. Blood. 1995; 86; 617-623. 3. Rao LVM, Huang AD, Rapaport SI. Thrombosis and Haemostasis. 1997; 73; 668-674. 4. Malia RG, Brookfield C, Bulman L, Greaves M. Thrombosis and Haemostasis. 1997; 78/2, 170 (OC-689). 5. Horbach DA, van Oort E, Donders RCJM, Derksen RHWM, de Groot PG, Thrombosis and Haemostasis. 1996; 76; 916-924. 6. Arnout J, Vanrusselt M, Wittevrongel C, Vermylen J. Thrombosis and Haemostasis. 1998; 79; 955-958. 7. Exner T Kraus M. Thrombosis and Haemostasis. 1999; 81; 470-471. 8. Husting MJ. et al. Clinical Chemistry. 1993; 89,583-591. 9. Galfe G, Milstein C. Preparation of monoclonal antibodies: Strategies and procedures. Methods Enzymol. 1981; 73; 3-46 10. Proctor RR. Rapaport SI. The partial thromboplastin time with kaolin. Am. J. Clin. Pathol. 1961; 36; 212-218. 11. Exner T. Diagnostic methodologies for circulating anticoagulants. Thrombosis and Haemostasis. 1985: 74: 338-344 SEQUENCE LISTING (1) GENERAL INFORMATION: (i) APPLICANT: (A) NAME: Gradipore Limited (B) STREET: 35-105 Delhi Road (C) CITY: North Ryde (D) STATE: New South Wales (E) COUNTRY: Australia (F) POSTAL CODE (ZIP): 2113 (A) NAME: Dade Behring Marburg GmbH (B) STREET: PO Box 1149 (C) CITY: Marburg (E) COUNTRY: Germany (F) POSTAL CODE (ZIP) : D-35001 (ii) TITLE OF INVENTION: Lupus Anticoagulant (iii) NUMBER OF SEQUENCES: 1 (iv) COMPUTER READABLE FORM: (A) MEDIUM TYPE: Floppy disk (B) COMPUTER: IBM PC compatible (C) OPERATING SYSTEM: PC-DOS/MS-DOS (D) SOFTWARE: Patentln Release #1.0, Version #1.30 (EPO) (2) INFORMATION FOR SEQ ID NO: 1: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 10 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 1: Cys Gly Ser Asp Arg Ala lie Glu Gly Arg 1 5 10

Claims: CLAIMS: 1. An isolated antibody directed against the Fl region of prothrombin, which antibody mimics the effect of a lupus anticoagulant (LA) in vitro. 2. The antibody according to claim 1 being a monoclonal antibody. 3. The antibody according to claim 2 obtained from a mouse following immunisation with human prothrombin. 3. The antibody according to claim 3 wherein the mouse is immunised with a N-terminal peptide derived from human prothrombin. 4. The antibody according to claim 4 wherein the N-terminal peptide derived from human prothrombin includes the amino acid sequence Cys-Gly- Ser-Asp-Arg-Ala-Ile-Glu-Gly-Arg (SEQ ID NO: 1). 5. The antibody according to any one of claims 1 to 4 wherein the antibody binds Fl.2 but not F2 region of prothrombin. 6. The antibody according to any one of claims 1 to 5 wherein selected from antibody designated 195/097a, 195/016, and 195/0155. 7. The antibody according to claim 6 being 195/097a. 8. Use of an isolated antibody according to any one of claims 1 to 7 in an in vitro blood clotting assay. 9. The use according to claim 8 wherein the assay is selected from the group consisting of activated partial thromboplastin time (APTT) test, kaolin clotting time (KCT), tissue thromboplastin inhibition test (TTIT), dilute Russell's viper venom time (DRWT), Taipan venom, and Textarin test. 10. The use according to claim 8 or 9 wherein the concentration of antibody is from 0.01 to 10 μmol. 11. The use according to claim 10 wherein the concentration of antibody is up to 0.7 μmol 12. A blood clotting test standard comprising normal human plasma treated or mixed with the antibody according to any one of claims 1 to 7. 13. The test standard according to claim 12 for use in blood clotting tests selected from the group consisting of activated partial thromboplastin time (APTT) test, kaolin clotting time (KCT), tissue thromboplastin inhibition test (TTIT), dilute Russell's viper venom time (DRWT), Taipan venom, and Textarin test. 14. A method of obtaining an antibody directed against the Fl region of prothrombin. which antibody mimics the effect of a lupus anticoagulant (LA) in vitro, the method comprising: (a) immunising an animal with prothrombin or a N-terminal peptide derived from human prothrombin; (b) testing for the production of an antibody by the animal which is capable of binding Fl.2 region of prothrombin but not capable of binding F2 region of prothrombin; and (c) isolating the antibody. 15. The method according to claim 14 wherein the animal is a mouse immunised with a peptide including the amino acid sequence Cys-Gly-Ser- Asp-Arg-Ala-Ile-Glu-Gly-Arg (SEQ ID NO: 1).

Inventors: EXNER THOMAS, KRAUS MICHAEL, EXNER, THOMAS, KRAUS, MICHAEL
Applicants: DADE BEHRING MARBURG GMBH, EXNER THOMAS, GRADIPORE LTD, KRAUS MICHAEL, EXNER, THOMAS, GRADIPORE LIMITED, KRAUS, MICHAEL
Application year: 1999
Main classification: C07K16
IPC codes: A61K39, C07K16, C12N15, C12P21, G01N33