[The role of HLA-B27 molecules in the pathogenesis of ankylosing spondylitis]

Hepatitis C virus modulates signal peptide peptidase to alter host protein processing

The mechanism by which hepatitis C virus (HCV) evades immune surveillance and causes chronic infection is unclear. We demonstrate here that HCV core protein interferes with the maturation of major histocompatibility complex (MHC) class I catalyzed by signal peptide peptidase (SPP) and induces degradation via HMG-CoA reductase degradation 1 homolog. In addition, we found that the core protein transmembrane domain is homologous to the human cytomegalovirus US2 protein, whose transmembrane region also targets SPP to impair MHC class I molecule expression in a similar manner. Therefore, our data suggest that SPP represents a potential target for the impairment of MHC class I molecules by DNA and RNA viruses.

Immunoevasins are viral proteins that prevent antigen presentation on major histocompatibility complex (MHC) class I, thus evading host immune recognition. Hepatitis C virus (HCV) evades immune surveillance to induce chronic infection; however, how HCV-infected hepatocytes affect immune cells and evade immune recognition remains unclear. Herein, we demonstrate that HCV core protein functions as an immunoevasin. Its expression interfered with the maturation of MHC class I molecules catalyzed by the signal peptide peptidase (SPP) and induced their degradation via HMG-CoA reductase degradation 1 homolog, thereby impairing antigen presentation to CD8⁺ T cells. The expression of MHC class I in the livers of HCV core transgenic mice and chronic hepatitis C patients was impaired but was restored in patients achieving sustained virological response. Finally, we show that the human cytomegalovirus US2 protein, possessing a transmembrane region structurally similar to the HCV core protein, targets SPP to impair MHC class I molecule expression. Thus, SPP represents a potential target for the impairment of MHC class I molecules by DNA and RNA viruses.

Quantitative Proteomic Analyses To Reveal the Key Features of Proteins in New Onset Ankylosing Spondylitis Patients

Ankylosing spondylitis (AS) is a chronic immune-mediated disease. Various immune cells play an essential role in the AS pathogenesis. However, the specific pathogenesis of AS has not been well understood. Proteomic profiles of peripheral blood mononuclear cells (PBMCs) were applied to reveal the specific pathogenesis of AS. Quantitative proteomic analyses were performed using liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based methods to investigate the protein profiling of PBMCs from new-onset AS patients (n = 9) and healthy controls (n = 9). We identified 782 differentially expressed proteins (DEPs) and 527 differentially phosphorylated proteins (DPPs) between AS patients and healthy controls. The subcellular location of DEPs and DPPs showed that most of the DEPs were from the cytoplasm (n = 296, 38%), were extracellular (n = 141, 18%), and from the nucleus (n = 114, 15%); most of the DPPs were from the cytoplasm (n = 37, 34%), nucleus (n = 35, 32%), and plasma membrane (n = 10, 9%). We further identified 89 proteins with both expression and phosphorylation differences. The functional annotation of the 89 differentially expressed and phosphorylated proteins enriched in the antigen processing and presentation pathway. Four DEPs with six phosphorylated positions were found in the antigen processing and presentation pathway. The differentially expressed and phosphorylated proteins may be helpful to uncover the pathogenesis of AS. The six AS-specific proteins may serve as candidate markers for AS diagnosis and new treatment targets.

The arthritis-associated HLA-B*27:05 allele forms more cell surface B27 dimer and free heavy chain ligands for KIR3DL2 than HLA-B*27:09

Objectives. HLA-B*27:05 is associated with AS whereas HLA-B*27:09 is not associated. We hypothesized that different interactions with KIR immune receptors could contribute to the difference in disease association between HLA-B*27:05 and HLAB*27:09. Thus, the objective of this study was to compare the formation of β2m-free heavy chain (FHC) including B27 dimers (B272) by HLA-B*27:05 and HLA-B*27:09 and their binding to KIR immunoreceptors.

Methods. We studied the formation of HLA-B*27:05 and HLA-B*27:09 heterotrimers and FHC forms including dimers in vitro and in transfected cells. We investigated HLA-B*27:05 and HLA-B*27:09 binding to KIR3DL1, KIR3DL2 and LILRB2 by FACS staining with class I tetramers and by quantifying interactions with KIR3DL2CD3ε-reporter cells and KIR3DL2-expressing NK cells. We also measured KIR expression on peripheral blood NK and CD4 T cells from 18 HLA-B*27:05 AS patients, 8 HLA-B27 negative and 12 HLA-B*27:05+ and HLA-B*27:09+ healthy controls by FACS staining.

Results. HLA-B*27:09 formed less B27₂ and FHC than HLA-B*27:05. HLA-B*27:05-expressing cells stimulated KIR3DL2CD3ε-reporter T cells more effectively. Cells expressing HLA-B*27:05 promoted KIR3DL2+ NK cell survival more strongly than HLA-B*27:09. HLA-B*27:05 and HLA-B*27:09 dimer tetramers stained KIR3DL1, KIR3DL2 and LILRB2 equivalently. Increased proportions of NK and CD4 T cells expressed KIR3DL2 in HLA-B*27:05+ AS patients compared with HLA-B*27:05+, HLA-B*27:09+ and HLA-B27− healthy controls.

Conclusion. Differences in the formation of FHC ligands for KIR3DL2 by HLA-B*27:05 and HLA-B*27:09 could contribute to the differential association of these alleles with AS.

New perspectives on the ligands and function of the killer cell immunoglobulin-like receptor KIR3DL2 in health and disease

KIR3DL2/CD158k/p140 is a three domain killer cell immunoglobulin-like receptor incorporating cytoplasmic immunoreceptor tyrosine inhibitory motifs, expressed as a disulphide-bonded dimer. KIR3DL2 is a framework gene within the KIR locus and is highly polymorphic, with 62 allelic variants possibly coding for protein reported. KIR3DL2 binds to HLA-A3 and -A11 in a peptide-dependent fashion and to B27 free heavy chain forms. In addition, KIR3DL2 can also function as an innate immune receptor for delivery of CpG DNA to TLR9 in NK cells. The increased levels of expression of KIR3DL2 compared with other KIR expressed by T cell subsets in healthy individuals suggest it may function as a default KIR receptor. KIR3DL2-expressing natural killer (NK) cells and IL17 secreting CD4 T cells have been implicated in the pathogenesis of ankylosing spondylitis. Moreover, KIR3DL2 expression delineates circulating and cutaneous lymphoma T cells in Sézary's syndrome. Here we discuss how the unique molecular attributes of KIR3DL2 impact on its function on NK and T cells and how this may relate to its role in disease.

Polymorphisms of KIRs gene and HLA-C alleles in patients with ankylosing spondylitis: possible association with susceptibility to the disease

INTRODUCTION

An emerging body of evidence is accumulating to suggest that killer cell immunoglobulin-like receptors (KIRs) and human leukocyte antigen (HLA) class I ligands contribute to the pathogenesis of diverse kinds of autoimmune diseases. However, the functional effects of their polymorphism remain largely unknown to date. Thus, the present study was undertaken to determine the association of the polymorphisms KIRs gene and HLA-C alleles with the susceptibility to ankylosing spondylitis (AS) by means of polymerase chain reaction/sequence-specific primers for genotyping KIRs from genomic DNA of 119 patients with AS together with 128 healthy donors as a control group.

RESULTS AND DISCUSSION

We found that the frequencies of KIR3DS1 and KIR2DL5 were statistically significantly higher in the patient group than those in the control group (P = 0.016 and P = 0.003, respectively). Meanwhile, the percentage of patients, who were carrying two or more of the activating KIRs, was higher than that of control group. With respect to HLA-C alleles, individuals with AS showed an increased frequency of HLA-Cw02. If HLA-C was divided into group 1 or group 2 based on whether there was an asparagine or lysine present at position 80 of the alpha-chain, HLA-C group 2 was more common in subjects with AS compared to control subjects. The genotype 2DS1+/HLA-C lys(80)+ was more common in subjects with AS. Moreover, the CD69 expression, a NK activation marker, remarkably increased in patient with AS.

CONCLUSION

In conclusions, this study suggests that KIR3DS1 may severe as AS susceptive genes to trigger continuous injury of arthrosis. The imbalance of activating and inhibitory KIR as well as HLA-C group 1 and group 2 may be the key factor, which influences the pathogenesis of AS. Moreover, KIR2DS1 might associate with the susceptibility of AS by influencing NK cell activity once group 2 HLA-C ligands are present.