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Parkinson's disease (PD) is a neurodegenerative disorder characterized by the progressive accumulation of α-synuclein aggregates in form of Lewy bodies. Genome-wide association studies have revealed that human leukocyte antigen (HLA) class II is a PD-associated gene, although the mechanisms linking HLA class II and PD remain elusive. Here, we identified a novel function of HLA class II in the transport of intracellular α-synuclein to the outside of cells. HLA class II molecules and α-synuclein formed complexes and moved to the cell surface at various degrees among HLA-DR alleles. HLA-DR with a DRB5∗01:01 allele, a putative PD-risk allele, substantially translocated normal and conformationally abnormal α-synuclein to the cell surface and extracellular vesicles. α-Synuclein/HLA class II complexes were found in A2058 melanoma cells, which express intrinsic α-synuclein and HLA-DR with DRB5∗01:01. Our findings will expand our knowledge of unconventional HLA class II function from autoimmune diseases to neurodegenerative disorders, shedding light on the association between the GWAS-prioritized PD-risk gene HLA-DR and α-synuclein.

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

Sialic acid immunoglobulin-like lectin (Siglec) family molecules are immune regulatory receptors that bind to specific molecules containing sialic acids. Varicella-zoster virus (VZV), a member of the herpesvirus family, infects hematopoietic cells and spreads throughout the body, causing chickenpox, shingles, and, sometimes fatal encephalomyelitis. However, the cellular entry receptors that are required for VZV to infect hematopoietic cells have remained unclear. Here, we found that Siglec-7, mainly expressed on hematopoietic cells, binds to VZV envelope glycoprotein B in a sialic acid-dependent manner. Furthermore, Siglec-7 mediated VZV infection by inducing membrane fusion. Our findings provide the first evidence for a molecular mechanism by which VZV infects hematopoietic cells.

PDF file - 117K, Genes up-regulated (>2.0) in Stat3delta/delta compared with Stat3flox/flox

PDF file - 63K, Up-regulated PPI network

PDF file - 126K, Genes down-regulated (

PDF file - 76K, Enriched KEGG pathway association (p

PDF file - 72K, The expression and activation of Stat3 was intact in both myeloid and lymphocyte lineages in Stat3delta/delta mice

Objective We previously reported that RF recognized the IgG heavy chain (IgGH)/RA-susceptible HLA class II molecule complex. In the present study, we investigated the molecular mechanisms underlying HLA binding to and the RF recognition of IgGH. Methods We synthesized various types of IgGH segments, including VH, CH1, CH2 and CH3, and transfected them with or without HLA class II molecules into the Human Embryonic Kidney 293T cell line. IgGH single domains linked with the HLA-Cw3 peptide, which binds to the binding groove of the HLA class II molecule, were also synthesized. The expression of IgGH domains on the cell surface and their recognition by RF were examined using flow cytometry. Results Flag-tagged IgGH segments containing CH1 (CH1, VH-CH1, CH1-CH2, VH-CH1-CH2, CH1-CH2-CH3 and VH-CH1-CH2-CH3) were clearly presented on the cell surface by HLA-DR4, while segments without the CH1 domain were expressed at a low level, and the CH3 single domain was only weakly detected on the cell surface, even with HLA-DR4. We then transfected IgGH single domains linked to the Cw3 peptide together with HLA-DR4 and showed that RF-containing sera from RA patients only recognized the CH3 domain and none of the other single domains. When various segments without the Cw3 peptide were transfected with HLA-DR4, only the CH1-CH2-CH3 segment and full-length IgGH were detected by the sera of RA patients. Conclusion The CH1 domain of IgGH binds to the RA-susceptible HLA-DR molecule and is expressed on the cell surface. RF specifically recognizes the CH3 domain of the IgGH/HLA-DR4 complex.

The Omicron variant continuously evolves under the humoral immune pressure obtained by vaccination and SARS-CoV-2 infection and the resultant Omicron subvariants exhibit further immune evasion and antibody escape. Engineered ACE2 decoy composed of high-affinity ACE2 and IgG1 Fc domain is an alternative modality to neutralize SARS-CoV-2 and we previously reported its broad spectrum and therapeutic potential in rodent models. Here, we show that engineered ACE2 decoy retains the neutralization activity against Omicron subvariants including the currently emerging XBB and BQ.1 which completely evade antibodies in clinical use. The culture of SARS-CoV-2 under suboptimal concentration of neutralizing drugs generated SARS-CoV-2 mutants escaping wild-type ACE2 decoy and monoclonal antibodies, whereas no escape mutant emerged against engineered ACE2 decoy. As the efficient drug delivery to respiratory tract infection of SARS-CoV-2, inhalation of aerosolized decoy treated mice infected with SARS-CoV-2 at a 20-fold lower dose than the intravenous administration. Finally, engineered ACE2 decoy exhibited the therapeutic efficacy for COVID-19 in cynomolgus macaques. Collectively, these results indicate that engineered ACE2 decoy is the promising therapeutic strategy to overcome immune-evading SARS-CoV-2 variants and that liquid aerosol inhalation can be considered as a non-invasive approach to enhance efficacy in the treatment of COVID-19.

OBJECTIVE Specific HLA class II alleles are associated with susceptibility to systemic lupus erythematosus (SLE). The role of HLA class II molecules in SLE pathogenesis remains unclear, although anti-DNA antibodies are specific to SLE and correlate with disease activity. We previously demonstrated that misfolded proteins bound to HLA class II molecules are specific targets for the autoantibodies produced in autoimmune diseases. This study was undertaken to validate our hypothesis that DNA binds to HLA class II molecules in a manner similar to that of misfolded proteins and that DNA bound to HLA class II molecules is involved in SLE pathogenesis. METHODS We analyzed the binding of DNA to HLA class II molecules, as well as the response of cells expressing anti-DNA B cell receptors (BCRs) to cells expressing the DNA/HLA class II complex. RESULTS Efficient binding of DNA to HLA class II molecules was observed in risk alleles of SLE, such as HLA-DRB1*15:01. The efficiency of DNA binding to each HLA-DR allele was positively associated with the risk of SLE conferred by the HLA-DR allele. In addition, reporter cells carrying anti-DNA BCRs were activated by cells expressing DNA/HLA class II complexes. CONCLUSION These results provide evidence that DNA bound to HLA class II molecules is involved in SLE pathogenesis.

Leukocyte immunoglobulin-like receptor B (LILRB), a family of immune checkpoint receptors, contributes to acute myeloid leukemia (AML) development, but the specific mechanisms triggered by activation or inhibition of these immune checkpoints in cancer is largely unknown. Here we demonstrate that the intracellular domain of LILRB3 is constitutively associated with the adaptor protein TRAF2. Activated LILRB3 in AML cells leads to recruitment of cFLIP and subsequent NF-κB upregulation, resulting in enhanced leukemic cell survival and inhibition of T-cell-mediated anti-tumor activity. Hyperactivation of NF-κB induces a negative regulatory feedback loop mediated by A20, which disrupts the interaction of LILRB3 and TRAF2; consequently the SHP-1/2-mediated inhibitory activity of LILRB3 becomes dominant. Finally, we show that blockade of LILRB3 signaling with antagonizing antibodies hampers AML progression. LILRB3 thus exerts context-dependent activating and inhibitory functions, and targeting LILRB3 may become a potential therapeutic strategy for AML treatment. Wu et al. show that LILRB3 modulates AML cell survival and antileukemic T-cell responses through regulation of TRAF2–cFLIP–NF-κB signaling and demonstrate the therapeutic efficacy of LILRB3-blocking antibodies in humanized PDX models in vivo.

Triggering receptor expressed on myeloid cells 2 (TREM2) plays crucial roles in Alzheimer’s disease (AD) by regulating microglia migration toward, and phagocytosis of oligomeric amyloid-β (oAβ) and amyloid plaques. Studies in rodent models of AD have shown that mice with increased TREM2 expression have reduced amyloid pathology. Here, we identified a TREM2 agonist monoclonal Ab (Ab18) by panning a phage-displayed single-chain variable fragment Ab library. By engineering the bivalent immunoglobulin G1 (IgG1) to tetra-variable domain immunoglobulin (TVD-Ig), we further increased the TREM2 activation by 100-fold. Stronger TREM2 activation led to enhanced microglia phagocytosis of the oAβ-lipid complex, migration toward oAβ, and improved microglia survival in vitro. Mechanistic studies showed increased TREM2 clustering on microglia by the tetravalent Ab18 TVD-Ig without altering microglial TREM2 amount. An engineered bispecific Ab targeting TREM2 and transferrin receptor (TfR; Ab18 TVD-Ig/αTfR) improved Ab brain entry by more than 10-fold with a broad brain parenchyma distribution. Weekly treatment of 5XFAD mice (a model of AD) with Ab18 TVD-Ig/αTfR showed a considerable reduction of amyloid burden with increased microglia migration to and phagocytosis of amyloid plaques, improved synaptic and neuronal marker intensity, improved cognitive functions, reduced endogenous tau hyperphosphorylation, and decreased phosphorylated neurofilament H immunostaining. This study demonstrated the feasibility of engineering multivalent TREM2 agonistic Ab coupled with TfR-mediated brain delivery to enhance microglia functions and reduce amyloid pathology in vitro and in vivo. This Ab engineering approach enables the development of effective TREM2-targeting therapies for AD.

The extracellular matrix (ECM) is the basis for virtually all cellular processes and is also related to tumor metastasis. Fibronectin (FN), a major ECM macromolecule expressed by different cell types and also present in plasma, consists of multiple functional modules that bind to ECM-associated, plasma, and cell-surface proteins such as integrins and FN itself, thus ensuring its cell-adhesive and modulatory role. Here we show that FN constitutes an immune checkpoint. Thus, FN was identified as a physiological ligand for a tumor/leukemia/lymphoma- as well as autoimmune-associated checkpoint, ILT3/LILRB4 (B4, CD85k). Human B4 and the murine ortholog, gp49B, bound FN with sub-micromolar affinities as assessed by bio-layer interferometry. The major B4-binding site in FN was located at the N-terminal 30-kDa module (FN30), which is apart from the major integrin-binding site present at the middle of the molecule. Blockade of B4–FN binding such as with B4 antibodies or a recombinant FN30-Fc fusion protein paradoxically ameliorated autoimmune disease in lupus-prone BXSB/Yaa mice. The unexpected nature of the B4–FN checkpoint in autoimmunity is discussed, referring to its potential role in tumor immunity.

Many patients with severe COVID-19 suffer from pneumonia, and thus elucidation of the mechanisms underlying the development of such severe pneumonia is important. The ORF8 protein is a secreted protein of SARS-CoV-2, whose in vivo function is not well understood. Here, we analyzed the function of ORF8 protein by generating ORF8-knockout SARS-CoV-2. We found that the lung inflammation observed in wild-type SARS-CoV-2-infected hamsters was decreased in ORF8-knockout SARS-CoV-2-infected hamsters. Administration of recombinant ORF8 protein to hamsters also induced lymphocyte infiltration into the lungs. Similar pro-inflammatory cytokine production was observed in primary human monocytes treated with recombinant ORF8 protein. Furthermore, we demonstrate that the serum ORF8 protein levels are correlated well with clinical markers of inflammation. These results demonstrated that the ORF8 protein is a viral cytokine of SARS-CoV-2 involved in the in the immune dysregulation observed in COVID-19 patients, and that the ORF8 protein could be a novel therapeutic target in severe COVID-19 patients.

Plasmodium falciparum causes the most severe form of malaria. Acquired immunity against P. falciparum provides insufficient protection even after repeated infections. Therefore, P. falciparum parasites might exploit inhibitory receptors for immune evasion. P. falciparum RIFINs are products of a multigene family consisting of 150–200 genes. Previously, we demonstrated that some RIFINs downregulate the immune response through the leukocyte immunoglobulin-like receptor (LILR) family inhibitory receptor, LILRB1, and leukocyte-associated immunoglobulin-like receptor 1, LAIR1. In this study, we further analyzed the expression of inhibitory receptor ligands on P. falciparum-infected erythrocytes and found that P. falciparum-infected erythrocytes expressed ligands for another LILR family inhibitory receptor, LILRB2, that recognizes HLA class I molecules as a host ligand. Furthermore, we identified that a specific RIFIN was a ligand for LILRB2 by using a newly developed RIFIN expression library. In addition, the domain 3 of LILRB2 was involved in RIFIN binding, whereas the domains 1 and 2 of LILRB2 were involved in the binding to HLA class I molecules. These results suggest that inhibitory receptor LILRB2 is also targeted by RIFIN for immune evasion of P. falciparum similar to LILRB1 and LAIR1.

Acquired immune reaction is initiated by dendritic cells (DCs), which present Ags to a few naive Ag-specific T cells. Deregulation of gene expression in DCs may alter the outcome of the immune response toward immunodeficiency and/or autoimmune diseases. Expression of TRIM28, a nuclear protein that mediates gene silencing through heterochromatin, decreased in DCs from old mice, suggesting alteration of gene regulation. Mice specifically lacking TRIM28 in DCs show increased DC population in the spleen and enhanced T cell priming toward inflammatory effector T cells, leading to acceleration and exacerbation in experimental autoimmune encephalomyelitis. TRIM28-deficient DCs were found to ectopically transcribe endogenous retrovirus (ERV) elements. Combined genome-wide analysis revealed a strong colocalization among the decreased repressive histone mark H3K9me3-transcribed ERV elements and the derepressed host genes that were related to inflammation in TRIM28-deficient DCs. This suggests that TRIM28 occupancy of ERV elements critically represses expression of proximal inflammatory genes on the genome. We propose that gene silencing through repressive histone modification by TRIM28 plays a role in maintaining the integrity of precise gene regulation in DCs, which prevents aberrant T cell priming to inflammatory effector T cells.

We have found that a novel autoantibody against β2-glycoprotein I (β2GPI)/human leukocyte antigen (HLA) class II complexes (anti-β2GPI/HLA-DR) is involved in the pathogenesis of antiphospholipid syndrome (APS). It was also found that many APS patients who were negative for conventional antiphospholipid antibodies (aPLs) possessed anti-β2GPI/HLA-DR. These results suggested that anti-β2GPI/HLA-DR measurements may be more sensitive for diagnosing APS than conventional aPLs tests. Recurrent pregnancy loss (RPL) is one of the clinical manifestations of APS. Therefore, a prospective, multicenter, cross-sectional study were conducted to assess whether anti-β2GPI/HLA-DR is also associated with RPL. This study of 227 couples with RPL revealed that 22.9% (52/227) of RPL women tested positive for anti-β2GPI/HLA-DR, and 24 (19.8%) of the 121 couples with unexplained RPL tested positive for anti-β2GPI/HLA-DR. Interestingly, thirty-five of the 52 (67.3%) RPL patients who were positive for anti-β2GPI/HLA-DR possessed no conventional aPLs of criteria. This novel autoantibody against β2GPI/HLA class II complexes may be a major risk factor for RPL, and it may be a promising biomarker for diagnosing APS.

Varicella-zoster virus (VZV) first infects hematopoietic cells, with the infected cells then acting to distribute the virus throughout the body. Sialic acid-binding immunoglobulin-like lectin (Siglec) family molecules recognize sialic acid-containing molecules on the same cell surface, called cis-ligands, or molecules on other cells or soluble agents, called trans-ligands. Among the Siglec family molecules, Siglec-4 and Siglec-7 mediate VZV infection through association with glycoprotein B (gB). As Siglec-7, but not Siglec-4, is expressed on hematopoietic cells such as monocytes, the regulatory mechanism by which Siglec-7 associates with gB is important to our understanding of VZV infection of blood cells. Here, we found that Siglec-7 is required for VZV to infect human primary monocytes. Furthermore, treatment of primary monocytes with sialidase enhanced both VZV gB binding to monocytes and VZV infectivity. Calcium influx in primary monocytes decreased the expression of Siglec-7 cis-ligands and increased VZV infectivity. These results demonstrate that the Siglec-7 cis-ligands present on primary monocytes play an important role in VZV infection through regulation of the interaction between gB and Siglec-7.

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.

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.

Several variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have emerged during the current coronavirus disease 2019 (COVID-19) pandemic. Although antibody cross-reactivity with the spike glycoproteins (S) of diverse coronaviruses, including endemic common cold coronaviruses (HCoVs), has been documented, it remains unclear whether such antibody responses, typically targeting the conserved S2 subunit, contribute to protection when induced by infection or through vaccination. Using a mouse model, we found that prior HCoV-OC43 S–targeted immunity primes neutralizing antibody responses to otherwise subimmunogenic SARS-CoV-2 S exposure and promotes S2-targeting antibody responses. Moreover, vaccination with SARS-CoV-2 S2 elicited antibodies in mice that neutralized diverse animal and human alphacoronaviruses and betacoronaviruses in vitro and provided a degree of protection against SARS-CoV-2 challenge in vivo. Last, in mice with a history of SARS-CoV-2 Wuhan–based S vaccination, further S2 vaccination induced broader neutralizing antibody response than booster Wuhan S vaccination, suggesting that it may prevent repertoire focusing caused by repeated homologous vaccination. These data establish the protective value of an S2-targeting vaccine and support the notion that S2 vaccination may better prepare the immune system to respond to the changing nature of the S1 subunit in SARS-CoV-2 variants of concern, as well as to future coronavirus zoonoses.

Several common-cold coronaviruses (HCoVs) are endemic in humans and several variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have emerged during the current Coronavirus disease 2019 (COVID-19) pandemic. Whilst antibody cross-reactivity with the Spike glycoproteins (S) of diverse coronaviruses has been documented, it remains unclear whether such antibody responses, typically targeting the conserved S2 subunit, contribute to or mediate protection, when induced naturally or through vaccination. Using a mouse model, we show that prior HCoV-OC43 S immunity primes neutralising antibody responses to otherwise subimmunogenic SARS-CoV-2 S exposure and promotes S2-targeting antibody responses. Moreover, mouse vaccination with SARS-CoV-2 S2 elicits antibodies that neutralise diverse animal and human alphacoronaviruses and betacoronaviruses in vitro, and protects against SARS-CoV-2 challenge in vivo. Lastly, in mice with a history of SARS-CoV-2 Wuhan-based S vaccination, further S2 vaccination induces stronger and broader neutralising antibody response than booster Wuhan S vaccination, suggesting it may prevent repertoire focusing caused by repeated homologous vaccination. The data presented here establish the protective value of an S2-targeting vaccine and support the notion that S2 vaccination may better prepare the immune system to respond to the changing nature of the S1 subunit in SARS-CoV-2 variants of concern (VOCs), as well as to unpredictable, yet inevitable future coronavirus zoonoses.

Genomic deletion of donor-patient-mismatched HLA alleles in leukemic cells is a major cause of relapse after allogeneic hematopoietic stem cell transplantation (HSCT). Mismatched HLA is frequently lost as an individual allele or a whole region in HLA-class I, however, it is downregulated in HLA-class II. We hypothesized that there might be a difference in T cell recognition capacity against epitopes associated with HLA-class I and HLA-class II and consequently such allogeneic immune pressure induced HLA alterations in leukemic cells. To investigate this, we conducted in vitro experiments with T cell receptor-transduced T (TCR-T) cells. The cytotoxic activity of NY-ESO-1-specific TCR-T cells exhibited similarly against K562 cells with low HLA-A*02:01 expression. However, we demonstrated that the cytokine production against low HLA-DPB1*05:01 expression line decreased gradually from the HLA expression level approximately 2-log lower than normal expressors. Using sort-purified leukemia cells before and after HSCT, we applied the next-generation sequencing, and revealed that there were several marked downregulations of HLA-class II alleles which demonstrated consistently low expression from pre-transplantation. The marked downregulation of HLA-class II may lead to decreased antigen recognition ability of antigen-specific T cells and may be one of immune evasion mechanism associated with HLA-class II downregulation.

Breakthrough infection is often observed for the SARS-CoV-2 Delta variant, and neutralizing antibody levels are associated with vaccine efficiency1. Recent studies revealed that not only anti-receptor binding domain (RBD) antibodies2 but also antibodies against the N-terminal domain (NTD) play important roles in positively3,4 or negatively4-8 controlling SARS-CoV-2 infectivity. Here, we found that the Delta variant completely escaped from anti-NTD neutralizing antibodies, while increasing responsiveness to anti-NTD infectivity-enhancing antibodies. Cryo-EM analysis of the Delta spike revealed that epitopes for anti-NTD neutralizing antibodies are structurally divergent, whereas epitopes for enhancing antibodies are well conserved with wild-type spike protein. Although Pfizer-BioNTech BNT162b2-immune sera neutralized the original Delta variant, when major anti-RBD neutralizing antibody epitopes remaining in the Delta variant were disrupted, some BNT162b2-immune sera not only lost neutralizing activity but became infection-enhanced. The enhanced infectivity disappeared when the Delta NTD was substituted with the wild-type NTD. Sera of mice immunized by Delta spike, but not wild-type spike, consistently neutralized the Delta variant lacking anti-RBD antibody epitopes without enhancing infectivity. Importantly, SARS-CoV-2 variants with similar mutations in the RBD have already emerged according to the GISAID database and their pseudoviruses were resistant to some BNT162b2-immune sera. These findings demonstrate that mutations in the NTD, as well as the RBD, play an important role in antibody escape by SARS-CoV-2. Development of effective vaccines against emerging variants will be necessary, not only to protect against infection, but also to prevent further mutation of SARS-CoV-2.

The major histocompatibility complex (MHC) is a central molecule in the immune system. The MHC is also a highly polymorphic gene that is the most strongly involved in susceptibility to many autoimmune diseases. Therefore, the elucidation of the mechanism by which specific MHC alleles are involved in autoimmune disease susceptibility is important to our understanding of the pathogenesis of autoimmune diseases. Specific autoantibody production is observed in many autoimmune diseases, but the mechanism underlying their production remains unclear. We have found 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 by MHC class II molecules of autoimmune disease risk alleles are major autoantibody targets. In this article, I propose a novel mechanism underlying autoimmune diseases mediated by misfolded proteins complexed with MHC class II molecules.

mRNA-based vaccines provide effective protection against most common SARS-CoV-2 variants. However, identifying likely breakthrough variants is critical for future vaccine development. Here, we found that the Delta variant completely escaped from anti-N-terminal domain (NTD) neutralizing antibodies, while increasing responsiveness to anti-NTD infectivity-enhancing antibodies. Although Pfizer-BioNTech BNT162b2-immune sera neutralized the Delta variant, when four common mutations were introduced into the receptor binding domain (RBD) of the Delta variant (Delta 4+), some BNT162b2-immune sera lost neutralizing activity and enhanced the infectivity. Unique mutations in the Delta NTD were involved in the enhanced infectivity by the BNT162b2-immune sera. Sera of mice immunized by Delta spike, but not wild-type spike, consistently neutralized the Delta 4+ variant without enhancing infectivity. Given the fact that a Delta variant with three similar RBD mutations has already emerged according to the GISAID database, it is necessary to develop vaccines that protect against such complete breakthrough variants.

BackgroundMicroglia plays crucial roles in Alzheimer’s disease (AD) development. Triggering receptor expressed on myeloid cells 2 (TREM2) in association with DAP12 mediates signaling affecting microglia function. Here we study the negative regulation of TREM2 functions by leukocyte immunoglobulin-like receptor subfamily B member 2 (LILRB2), an inhibitory receptor bearing ITIM motifs.MethodsTo specifically interrogate LILRB2-ligand (oAβ and PS) interactions and microglia functions, we generated potent antagonistic LILRB2 antibodies with sub-nanomolar level activities. The biological effects of LILRB2 antagonist antibody (Ab29) were studied in human induced pluripotent stem cell (iPSC)–derived microglia (hMGLs) for migration, oAβ phagocytosis, and upregulation of inflammatory cytokines. Effects of the LILRB2 antagonist antibody on microglial responses to amyloid plaques were further studied in vivo using stereotaxic grafted microglia in 5XFAD mice.ResultsWe confirmed the expression of both LILRB2 and TREM2 in human brain microglia using immunofluorescence. Upon co-ligation of the LILRB2 and TREM2 by shared ligands oAβ or PS, TREM2 signaling was significantly inhibited. We identified a monoclonal antibody (Ab29) that blocks LILRB2/ligand interactions and prevents TREM2 signaling inhibition mediated by LILRB2. Further, Ab29 enhanced microglia phagocytosis, TREM2 signaling, migration, and cytokine responses to the oAβ-lipoprotein complex in hMGL and microglia cell line HMC3. In vivo studies showed significantly enhanced clustering of microglia around plaques with a prominent increase in microglial amyloid plaque phagocytosis when 5XFAD mice were treated with Ab29.ConclusionsThis study revealed for the first time the molecular mechanisms of LILRB2-mediated inhibition of TREM2 signaling in microglia and demonstrated a novel approach of enhancing TREM2-mediated microglia functions by blocking LILRB2-ligand interactions. Translationally, a LILRB2 antagonist antibody completely rescued the inhibition of TREM2 signaling by LILRB2, suggesting a novel therapeutic strategy for improving microglial functions.

SummarySARS-CoV-2 Lambda, a new variant of interest, is now spreading in some South American countries; however, its virological features and evolutionary trait remain unknown. Here we reveal that the spike protein of the Lambda variant is more infectious and it is attributed to the T76I and L452Q mutations. The RSYLTPGD246-253N mutation, a unique 7-amino-acid deletion mutation in the N-terminal domain of the Lambda spike protein, is responsible for evasion from neutralizing antibodies. Since the Lambda variant has dominantly spread according to the increasing frequency of the isolates harboring the RSYLTPGD246-253N mutation, our data suggest that the insertion of the RSYLTPGD246-253N mutation is closely associated with the massive infection spread of the Lambda variant in South America.HighlightsLambda S is highly infectious and T76I and L452Q are responsible for this propertyLambda S is more susceptible to an infection-enhancing antibodyRSYLTPGD246-253N, L452Q and F490S confer resistance to antiviral immunityGraphical Abstract

Through single-cell TCR and RNA sequencing, the authors identified public cTfh clonotypes expanded in recovered COVID-19 patients and determined their epitopes in the specific regions of spike protein conserved among emerging SARS-CoV-2 variants, which are candidates for booster antigens., Adaptive immunity is a fundamental component in controlling COVID-19. In this process, follicular helper T (Tfh) cells are a subset of CD4+ T cells that mediate the production of protective antibodies; however, the SARS-CoV-2 epitopes activating Tfh cells are not well characterized. Here, we identified and crystallized TCRs of public circulating Tfh (cTfh) clonotypes that are expanded in patients who have recovered from mild symptoms. These public clonotypes recognized the SARS-CoV-2 spike (S) epitopes conserved across emerging variants. The epitope of the most prevalent cTfh clonotype, S864–882, was presented by multiple HLAs and activated T cells in most healthy donors, suggesting that this S region is a universal T cell epitope useful for booster antigen. SARS-CoV-2–specific public cTfh clonotypes also cross-reacted with specific commensal bacteria. In this study, we identified conserved SARS-CoV-2 S epitopes that activate public cTfh clonotypes associated with mild symptoms.

ObjectivesRecent evidences have revealed that anti-SSA/SSB antibodies, the major autoantibodies in Sjögren's syndrome (SS), are produced in salivary glands. This study aims to clarify overall of autoantibody production at lesion site, including anti-centromere antibody (ACA)-positive SS.MethodsAntibodies of antibody-secreting cells in human salivary glands were produced as recombinant antibodies. The reactivity of these antibodies and their revertants were investigated by ELISA and newly developed antigen-binding beads assay, which can detect conformational epitopes. The target of uncharacterised antibodies was identified by immunoprecipitation and mass spectrometry. Autoantibody-secreting cells in salivary gland tissue were identified by immunohistochemistry using green fluorescent protein-autoantigen fusion proteins.ResultsA total of 256 lesion antibodies were generated, and 69 autoantibodies including 24 ACAs were identified among them. Beads assay could detect more autoantibodies than ELISA, suggesting autoantibodies target to antigens with native conformation. After somatic hypermutations were reverted, autoantibodies drastically decreased antigen reactivity. We showed that MIS12 complex, a novel target of ACA, and CENP-C are major targets of ACA produced in salivary glands by examining cloned antibodies and immunohistochemistry, whereas few anti-CENP-B antibodies were detected. The target profiling of serum ACA from 269 patients with SS, systemic sclerosis (SSc), primary biliary cirrhosis (PBC) and healthy controls revealed that ACA-positive patients have antibodies against various sites of centromere complex regardless of disease.ConclusionWe showed direct evidences of antigen-driven maturation of anti-SSA/SSB antibody and ACA in SS lesion. ACA recognises centromere ‘complex’ rather than individual protein, and this feature is common among patients with SS, SSc and PBC.