ANTI-PHOSPHATIDYLSERINE/PROTHROMBIN ANTIBODIES AND VASCULAR EVENTS ASSOCIATE POSITIVELY WITH HLA-DRB1*13 AND NEGATIVELY WITH HLA-DRB1*03 IN SLE

• Anti-phosphatidylserine/prothrombin antibodies (anti-PS/PT) associate with thrombotic events (1). HLA-DRB1 alleles contribute to the occurrence of conventional antiphospholipid antibodies (aPL), including anti-beta2glycoprotein-I (beta2GPI) and anti-cardiolipin (CL) (2).ObjectivesWe investigated associations between anti-PS/PT and HLA-DRB1 alleles and thrombosis in patients with SLE. Conventional aPL were included for comparison.MethodsWe included 341 consecutive Swedish SLE patients, with information on general cardiovascular risk factors, including blood lipids, lupus anticoagulant (LAC) and thrombotic events. Anti-PS/PT, anti-beta2GPI and anti-CL of IgA/G/M isotypes were quantified in parallel using particle-based multi-analyte technology. The 99th percentiles among 162 age- and sex-matched populations controls were used as cutoffs. HLA-DRB1 typing was performed using sequence-specific primer PCR.ResultsAnti-PS/PT antibodies associated positively with HLA-DRB1*13 (odds ratio [OR] 2.7, P=0.002), whereas anti-beta2GPI and anti-CL antibodies associated primarily with HLA-DRB1*04 (OR 2.5, P=0.0005; Table 1). These associations remained after adjustment for other significant HLA-DRB1 alleles identified in Table 1 (Figure 1a and b) also for LAC (Figure 1c), and also after adjustment for age and gender (not shown). HLA-DRB1*13, but not DRB1*04, remained as an independent risk factor for thrombosis after adjustment for significant HLA alleles (Figure 1d), and also after adjustment for cardiovascular risk factors in stepwise regression (not shown). Mediation analysis showed that 31.3% of the HLA-DRB1*13-related risk for thrombosis was mediated by anti-PS/PT positivity. HLA-DRB1*03, on the other hand, associated negatively with thrombotic events (Figure 1d) as well as with all aPL (Figure 1a-c). HLA-DRB1*03 had thrombo-protective effect in aPL positive patients (Figure 1d). Additionally, HLA-DRB1*03 positivity was associated with a favourable lipid profile regarding high-density lipoprotein (median 1.4 vs. 1.2 mmol/L, p=0.02) and triglycerides (median 0.9 vs 1.1 mmol/L, p=0.04); whereas no other HLA-DRB1 alleles showed any associations to lipid levels.Table 1.Frequency of individual HLA DRB1 and associations with antibody phenotypes. Odds ratios (OR) and confidence intervals (CI) for being antibody positive given a specific HLA allele and corresponding p values were calculated using Chi2 tests, with significant associations underlined.HLA DRB1HLA-DRB1 n (%) total patientsAnti-PS/PT positive (any isotype) n=48OR (95%CI); PAnti-β2GPI or anti-CL positive (any isotype) n=96OR (95%CI); P*0141 (12.9%)4 (8.3%)0.6 (0.2-1.7); 0.311 (11.4%)0.8 (0.4-1.7); 0.6*03147 (46.5%)13 (27.1%)0.4 (0.2-0.7); 0.00433 (34.4%)0.5 (0.3-0.8); 0.006*0494 (29.7%)18 (37.5%)1.6 (0.8-2.9); 0.241 (42.7%)2.5 (1.5-4.1); 0.0005*0728 (8.9%)6 (12.5%)1.5 (0.6-4); 0.49 (9.4%)1 (0.4-2.4); 0.9*0828 (8.9%)6 (12.5%)1.6 (0.6-4.3); 0.39 (9.4%)1.2 (0.5-2.7); 0.7*099 (2.8%)1 (2.1%)0.7 (0.1-5.5); 0.72 (2.1%)0.6 (0.1-3.0); 0.5*107 (2.2%)0 (0)NA2 (2.1%)0.9 (0.2-4.6); 0.9*1127 (8.5%)6 (12.5%)1.6 (0.6-4.3); 0.38 (8.3%)0.9 (0.4-2.2); 0.8*127 (2.2%)0 (0)NA1 (1%)0.4 (0.05-3.7); 0.4*1379 (25%)21 (43.7%)2.7 (1.4-5.2); 0.00233 (34.3%)2 (1.2-3.4%); 0.01*146 (1.9%)2 (4.2%)3.7 (0.6-23); 0.12 (2.1%)1.4 (0.2-8.9); 0.8*15118 (37.3%)12 (48%)0.5 (0.2-0.9); 0.04527 (28.1%)0.5 (0.3-0.9); 0.01*168 (2.5%)1 (2.1%)0.8 (0.09-6.4); 0.84 (4.2%)2.2 (0.5-9.2); 0.2ConclusionHLA-DRB1*13 confers risk for both anti-PS/PT and thrombotic events in SLE. The association between HLA-DRB1*13 and thrombosis is largely, but not entirely, mediated through anti-PS/PT. Due to the negative association of HLA-DRB1*03 with aPL and the positive association with favourable lipid levels, HLA-DRB1*03 seems to identify a subgroup of SLE patients with reduced vascular risk.References[1]Elbagir S et al. Lupus 2021;30(8):1289.[2]Lundström E et al. Ann Rheum Dis 2013;72:1018.Disclosure of InterestsSahwa Elbagir: None declared, Lina M. Diaz-Gallo: None declared, Giorgia Grosso: None declared, Agneta Zickert: None declared, Iva Gunnarsson: None declared, Michael Mahler Employee of: Dr Mahler is employee of Werfen., Elisabet Svenungsson Speakers bureau: Dr Svennungson has obtained speaker’s fees from Janssen., Grant/research support from: Dr Svennungson has obtained research grant from Merck., Johan Rönnelid Speakers bureau: Dr Rönnelid has given paid lectures for Thermo Fisher Scientific., Consultant of: Dr Rönnelid has been a member of the Scientific Advisory Board for Thermo Fisher Scientific.

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