Novel autoantibody against the β2‐glycoprotein I/human leucocyte antigen– DR complex in patients with refractory cutaneous ulcers

Association of anti-β2-glycoprotein I/HLA-DR complex antibody with arterial thrombosis in female patients with systemic rheumatic diseases

BACKGROUND

β2-glycoprotein I (β2GPI) complexed with human leukocyte antigen DR (β2GPI/HLA-DR) was found to be a major autoantibody target in antiphospholipid syndrome (APS). This study aimed to reveal the association between anti-β2GPI/HLA-DR antibodies and vascular thromboses in women with systemic rheumatic diseases.

METHODS

We conducted a retrospective longitudinal study. We measured anti-β2GPI/HLA-DR antibodies and compared them with anti-phospholipid antibody (aPL) profiles and the adjusted global antiphospholipid syndrome score (aGAPSS). Using receiver operating characteristic (ROC) analysis, we determined the best cut-off value for arterial thrombosis. We also evaluated the validity of anti-β2GPI/HLA-DR antibodies by adding to conventional cardiovascular risk factors in multivariate logistic analysis.

RESULTS

We evaluated 704 patients, including 66 (obstetric or thrombotic) APS, 13 primary APS, and 78 asymptomatic aPL carriers. Seventy-seven patients had a history of arterial thrombosis, and 14 patients had both arterial and venous thrombosis. These 14 patients, as well as patients with aGAPSS > 10 or triple-positive aPL profiles, displayed high anti-β2GPI/HLA-DR antibody titers. The ROC curve showed a sensitivity, specificity, and area under the curve (AUC) for arterial thrombosis of 33.8%, 91.4%, and 0.6009, respectively, with a cut-off value of 172.359 U/mL. The anti-β2GPI/HLA-DR antibody positivity using this cut-off value yielded an odds ratio of 5.13 (95%CI: 2.85-9.24), significantly improving the AUC from 0.677 to 0.730.

CONCLUSION

Anti-β2GPI/HLA-DR antibodies are associated with arterial thrombosis in female patients with systemic rheumatic diseases.

Evidence for Correlation between Novel Autoantibody against Phospholipid Named Neoself Anti-β2-GPI/HLA-DR Antibody and Complement Consumption in Infertile Patients

Impaired implantation is one of the causes of infertility. It occurs under vital inflammatory status due to immune hyperactivation. In the innate immune system, the inflammatory response to pathogenic stimuli is initiated by complement activation. Minimal vasculitis associated with complement consumption in infertile patients may be an underlying mechanism for impaired implantation. Antiphospholipid antibodies regulate the inflammatory response. Recently, a novel autoantibody (neoself antibody) against a complex of β2-GPI and HLA class II molecules (β2-GPI/HLA-DR) has been reported to be an independent autoantibody associated with aPLs. This study investigated the relationship between neoself antibodies and complement consumption in infertile patients with impaired implantation. It was found that decreased C4 levels were strongly related to the increased neoself antibody titers in the serum among those patients whose antibody titers were not as high. On the contrary, serum levels of CH50 and CRP are not correlated with them. These results suggest that neoself antibodies might indicate low-grade inflammation, which causes endometrial vasculitis in impaired implantation of infertile patients.

Anti-β2-glycoprotein I/HLA-DR Antibody and Adverse Obstetric Outcomes

Anti-β2-glycoprotein I/HLA-DR (anti-β2GPI/HLA-DR) antibody has been reported to be associated with antiphospholipid syndrome and recurrent pregnancy loss (RPL). We conducted a prospective multicenter cross-sectional study aimed at evaluating whether the anti-β2GPI/HLA-DR antibody is associated with adverse obstetric outcomes and RPL. From 2019 to 2021, serum anti-β2GPI/HLA-DR antibody levels (normal, <73.3 U) were measured in 462 women with RPL, 124 with fetal growth restriction (FGR), 138 with hypertensive disorders of pregnancy (HDP), 71 with preterm delivery before 34 gestational weeks (preterm delivery (PD) ≤ 34 GWs), and 488 control women who experienced normal delivery, by flow cytometry analysis. The adjusted odds ratios (aORs) of anti-β2GPI/HLA-DR antibody positivity for adverse obstetric outcomes and RPL were evaluated on the basis of comparisons between the control and each patient group, using multivariable logistic regression analysis. The following were the positivity rates for the anti-β2GPI/HLA-DR antibody in the patient and control groups: RPL, 16.9%; FGR, 15.3%; HDP, 17.4%; PD ≤ 34 GWs, 11.3%; and the control, 5.5%. It was demonstrated that anti-β2GPI/HLA-DR antibody positivity was a significant risk factor for RPL (aOR, 3.3 [95% confidence interval {CI} 1.9-5.6], p < 0.001), FGR (2.7 [1.3-5.3], p < 0.01), and HDP (2.7 [1.4-5.3], p < 0.01) although not for PD ≤ 34 GWs. For the first time, our study demonstrated that the anti-β2GPI/HLA-DR antibody is involved in the pathophysiology underlying FGR and HDP, as well as RPL.

Abrogation of self-tolerance by misfolded self-antigens complexed with MHC class II molecules

Specific MHC class II alleles are strongly associated with susceptibility to various autoimmune diseases. Although the primary function of MHC class II molecules is to present peptides to helper T cells, MHC class II molecules also function like a chaperone to transport misfolded intracellular proteins to the cell surface. In this study, we found that autoantibodies in patients with Graves' disease preferentially recognize thyroid-stimulating hormone receptor (TSHR) complexed with MHC class II molecules of Graves' disease risk alleles, suggesting that the aberrant TSHR transported by MHC class II molecules is the target of autoantibodies produced in Graves' disease. Mice injected with cells expressing mouse TSHR complexed with MHC class II molecules, but not TSHR alone, produced anti-TSHR autoantibodies. These findings suggested that aberrant self-antigens transported by MHC class II molecules exhibit antigenic properties that differ from normal self-antigens and abrogate self-tolerance, providing a novel mechanism for autoimmunity.

Cell surface-expressed Ro52/IgG/HLA-DR complex is targeted by autoantibodies in patients with inflammatory myopathies

Intracellular proteins are often targeted by autoantibodies in autoimmune diseases; however, the mechanism through which intracellular molecules are targeted remains unknown. We previously found that several intracellular misfolded proteins are transported to the cell surface by HLA class II molecules and are recognized by autoantibodies in some autoimmune diseases, such as rheumatoid arthritis, antiphospholipid syndrome, and microscopic polyangiitis. Ro52 is an intracellular Fc receptor that is a target antigen for myositis-associated autoantibodies. We analyzed the role of HLA class II molecules in the autoantibody recognition of Ro52. Ro52 alone was not transported to the cell surface by HLA class II molecules; however, it was transported to the cell surface in the presence of both IgG heavy chain and HLA class II molecules to form a Ro52/IgG/HLA-DR complex. The Ro52/IgG/HLA-DR complex was specifically recognized by autoantibodies from some patients with inflammatory myopathies. We then evaluated 120 patients with inflammatory myopathies with four types of myositis-specific antibodies and analyzed the autoantibodies against the Ro52/IgG/HLA-DR complex. The specific antibodies against the Ro52/IgG/HLA-DR complex were detected in 90% and 93% of patients who were positive for anti-MDA5 and anti-ARS antibodies, respectively. In individual patients with these two inflammatory myopathies, changes in serum titers of anti-Ro52/IgG/HLA-DR-specific antibodies were correlated with the levels of KL-6 (R = 0.51 in anti-MDA5 antibody-positive DM patients, R = 0.67 in anti-ARS antibody-positive PM/DM patients with respiratory symptoms) and CK (R = 0.63 in anti-ARS antibody-positive PM/DM patients with muscle symptoms) over time. These results suggest that antibodies against Ro52/IgG/HLA-DR expressed on the cell surface could be involved in the pathogenesis of inflammatory myopathy subgroups.

MHC: new insights from old molecules into the pathogenesis of autoimmunity

The major histocompatibility complex (MHC) is a central molecule in the immune system. The MHC is also a highly polymorphic gene that is strongly involved in susceptibility to many autoimmune diseases. Therefore, the elucidation of the mechanism by which specific MHCs are involved in disease pathogenesis is important to our understanding of the pathogenesis of autoimmune diseases. On the other hand, the production of autoantibodies is observed in many autoimmune diseases, but the mechanism underlying their production remains unclear. We have shown that MHC class II molecules exhibit a chaperone-like function to transport misfolded proteins in the endoplasmic reticulum to the outside of cells. Furthermore, misfolded proteins transported to the cell surface have been shown to be the targets of various autoantibodies produced in autoimmune diseases. In this article, I describe novel mechanisms underlying autoimmune diseases mediated by misfolded proteins complexes with MHC class II.

The β 2 -Glycoprotein I/HLA-DR Complex As a Major Autoantibody Target in Obstetric Antiphospholipid Syndrome

OBJECTIVE

The clinical manifestations of antiphospholipid syndrome (APS) include vascular thrombosis and pregnancy morbidity as well as recurrent pregnancy loss (RPL). However, in more than half of patients with RPL, the cause is never determined. Recently, β₂ -glycoprotein I (β₂ GPI) complexed with HLA class II molecules (β₂ GPI/HLA-DR) was found to be a major autoantibody target in APS. The present study was undertaken to assess the serum levels of autoantibodies against the β₂ GPI/HLA II complex as a potential risk factor for RPL in women.

METHODS

Serum levels of antiphospholipid antibodies (aPLs), including IgG/IgM anticardiolipin antibodies, IgG/IgM anti-β₂ GPI antibodies, and lupus anticoagulant as well as anti-β₂ GPI/HLA-DR antibodies, were measured in 227 women with RPL. In this prospective, multicenter, cross-sectional study, women with RPL and their partners underwent HLA-DR immunotyping and analysis to identify potential causes and risk factors associated with RPL. The normal range for anti-β₂ GPI/HLA-DR antibody levels was determined using serum samples obtained from a control population of female subjects (208 women of childbearing potential).

RESULTS

Of the 227 women with RPL, aPL antibodies were detected in 19.8%, and 52 (22.9%) tested positive for anti-β₂ GPI/HLA-DR antibodies. Among the 227 women, 121 (53.3%) had no risk factors for RPL, and among these women with unexplained RPL, 24 (19.8%) were positive for anti-β₂ GPI/HLA-DR antibodies. Of the 112 women who had clinical symptoms of APS but did not have levels of aPLs that met the diagnostic criteria for APS, 21 (18.8%) were positive for anti-β₂ GPI/HLA-DR antibodies.

CONCLUSION

The anti-β₂ GPI/HLA-DR antibody is frequently associated with RPL. Detection of these autoantibodies is useful in understanding the pathogenesis of RPL. Our findings may provide potential new therapeutic strategies for addressing RPL in patients with obstetric APS.

FcγRIIIA-mediated activation of NK cells by IgG heavy chain complexed with MHC class II molecules

Natural killer (NK) cells are a major FcγRIIIA-expressing lymphocyte population that mediate antibody-dependent cellular cytotoxicity. Although NK cells are critical for immunity against viruses and tumors, they are also activated in the joints of patients with rheumatoid arthritis (RA) and may be involved in disease progression. We previously found that human leukocyte antigen (HLA) class II molecules transport misfolded cellular proteins, such as IgG heavy chain (IgGH), to the cell surface via association with their peptide-binding grooves. Furthermore, we found that IgGHs bound to HLA class II molecules encoded by RA susceptibility alleles are specific targets for rheumatoid factor, an auto-antibody involved in RA. Here, we report that IgGHs bound to HLA class II molecules preferentially stimulate FcγRIIIA-expressing but not FcγRI-expressing cells. A significant correlation was observed between the reactivity of FcγRIIIA-expressing cells to IgGH complexed with a specific HLA-DR allele and the odds ratio for HLA-DR allele's association with RA. Moreover, primary human NK cells expressing FcγRIIIA demonstrated IFN-γ production and cytotoxicity against cells expressing IgGH complexed with HLA class II molecules. Our findings suggest that IgGH complexed with HLA class II molecules are involved in the activation of FcγRIIIA-expressing NK cells observed within arthritic joints.