Functional modulation of expanded CD8+ synovial fluid T cells by NK cell receptor expression in HLA-B27-associated reactive arthritis

[Role of innate receptors in chronic inflammation and autoimmunity]

Elucidating the basis of chronic disease courses and the development of appropriate treatment methods for inflammatory diseases still represent a big challenge for medical science, as the mechanisms driving aberrant immune reactions are mostly still unknown. Of particular interest is the identification of checkpoints that regulate the function and differentiation of proinflammatory cells during the pathogenesis, along with methods for modulation of specific checkpoints as a treatment approach. Innate receptors, such as members of the natural killer group 2 family (NKG2X), natural cytotoxicity receptors (NCR) or Toll-like receptors (TLRs), play an important role in modulating the immune response. NKG2 member D (NKG2D) is a potent activating receptor of the immune system, known as a sentinel for cellular danger signals presented by cells exposed to endoplasmic reticulum (ER) stress, cell death or an inflammatory cytokine milieu. NKG2A/C bind the non-classical HLA class I molecule, sense changes in ligand expression associated with malignant transformation and cellular stress and their main function is to send inhibitory or activating signals to NK cells and subsets of T cells. In this review, we present our latest knowledge on the understanding of the role of innate receptors in the context of chronic inflammation and autoimmunity with special emphasis on danger sensor receptors NKG2D and NKG2A/C.

Activation-Induced Killer Cell Immunoglobulin-like Receptor 3DL2 Binding to HLA-B27 Licenses Pathogenic T Cell Differentiation in Spondyloarthritis

Objective

In thespondyloarthritides (SpA), increased numbers of CD4+ T cells express killer cell immunoglobulin‐like receptor 3DL2 (KIR‐3DL2). The aim of this study was to determine the factors that induce KIR‐3DL2 expression, and to characterize the relationship between HLA–B27 and the phenotype and function of KIR‐3DL2–expressing CD4+ T cells in SpA.

Methods

In total, 34 B27+patients with SpA, 28 age‐ and sex‐matched healthy controls (20 B27− and 8 B27+), and 9 patients with rheumatoid arthritis were studied. KIR-3DL2 expression and other phenotypic characteristics of peripheral blood and synovial fluid CD4+ T cells were studied by flow cytometry, quantitative polymerase chain reaction, and Western blotting. T cell receptor clonality was determined by template‐switch anchored reverse transcription–polymerase chain reaction and sequencing analysis. Cytokines were measured by enzyme‐linked immunosorbent assay.

Results

Cellular activation induced KIR‐3DL2 expression on both naive and effector CD4+ T cells. KIR‐3DL2 binding to B27+ cells promoted expression of KIR‐3DL2, the Th17‐specific transcription factor retinoic acid receptor–related orphan nuclear receptor γt, and the antiapoptotic factor B cell lymphoma 2. KIR‐3DL2+CD4+ T cells in patients with ankylosing spondylitis were oligoclonal and enriched for markers of T cell activation and for the gut homing receptor CCR9. In the presence of B27+ antigen‐presenting cells, KIR‐3DL2+CD4+ T cells produced less interleukin‐2 (IL‐2) but more IL‐17. This effect was blocked by HC10, an antibody that inhibits the binding of KIR‐3DL2 to B27 heavy chains.

Conclusion

KIR‐3DL2 binding to HLA–B27 licenses Th17 cell differentiation in SpA. These findings raise the therapeutic potential of targeting HLA–B27–KIR‐3DL2 interactions for the treatment of B27+ patients with SpA.

Downregulation of immunoglobulin-like transcript-4 (ILT4) in patients with psoriatic arthritis

OBJECTIVE

The immunoglobulin-like transcript-4 (ILT4) is an inhibitory receptor that modulates the activity of innate immune agents. We determined the expression of ILT4 and analysed the relationship with the expression of costimulatory proteins and tumor necrosis factor-α (TNF-α) production in monocytes from patients with psoriatic arthritis (PsA) starting anti-TNF treatment.

METHODS

Peripheral blood monocytes from 15 healthy controls and from 16 patients with PsA were activated in vitro by CD40 ligand (CD40L) and analyzed for ILT4, CD40, CD80 and CD86 expression, and spontaneous lipopolysaccharide (LPS)-induced TNF-α production by flow cytometry, before and after treatment with adalimumab.

RESULTS

The percentage of ILT4-negative monocytes was greater in PsA patients compared to controls and negatively correlated with DAS44. Normal monocytes treated with sera of PsA patients showed a reduced expression of ILT4 compared with monocytes exposed to sera from controls. CD40, CD80 and CD86 expression was higher in patients compared to controls. Both spontaneous and LPS-induced TNF-α production was restricted to ILT4-negative monocytes and was greater in PsA patients compared to controls. Finally, twelve weeks-treatment with adalimumab resulted in a significant increase of ILT4 expression and a decrease of costimulatory molecules expression in PsA patients, compared to pre-therapy levels.

CONCLUSIONS

These data support the possibility that changes in the immunophenotype of monocytes play a role in the pathogenesis of PSA. Thus, modulation of the expression of ILT4 may represent an enticing new therapeutic target.

Association of KIR genotype with susceptibility to HLA-B27-positive ankylosing spondylitis

OBJECTIVE

Recent studies have explored the role of killer cell immunoglobulin-like receptors (KIRs) in chronic autoimmune diseases. The purpose of this study was to demonstrate whether KIR genes contribute to the pathogenesis of ankylosing spondylitis (AS) in Chinese populations.

METHODS

Sixteen KIR genes were genotyped from 60 unrelated patients with AS and 60 HLA-B27-positive matched healthy controls by PCR-SSP. The frequencies of the KIR alleles and genotypes in the AS and control groups were assessed by the χ(2) test.

RESULTS

Our results showed that the frequency of the activator receptor KIR3DS1 gene in the AS group was significantly increased compared to the controls (χ(2) = 5.263, P = 0.006, OR = 3.059, 95 % CI = 1.357-6.896). Moreover, the frequency of the KIR3DL1/3DS1 genotype was greater in the AS group than in the control group (P = 0.039, OR = 3.059, 95 % CI = 1.357-6.896). In contrast, the frequency of the no KIR3DL1/no 3DS1 genotype was lower in patients with AS compared with the controls (P = 0.032, OR = 0.110, 95 % CI = 0.013-0.911).

CONCLUSION

KIR3DS1, in addition to HLA-B27, may play an important independent role in the pathogenesis of AS in the Chinese population.

Permanent silencing of NKG2A expression for cell-based therapeutics

Natural killer (NK) and T-cell cytotoxicity is significantly reduced by signaling via CD94/NKG2A receptors. High levels of NKG2A on NK cells have been shown to compromise the graft-versus-leukemia effect in hematopoietic stem cell transplantation. We therefore evaluated the functional relevance of NKG2A silencing for the cytotoxic potential of genetically engineered NK and T cells. Lentiviral vectors containing short hairpin RNA (shRNA) sequences targeting NKG2A transcripts were used to transduce NKG2A(+) primary NK and T cells. NKG2A expression levels were measured by flow cytometry and real-time PCR. The effect of NKG2A silencing on the cytolytic potential of NK and T cells was evaluated in cytotoxicity assays using K562 and B lymphoblastoid cells as targets. Granzyme B mRNA transcript levels were detected by real-time PCR. The transduction of inducible RNAi cassettes containing the sequences for shRNAs targeting NKG2A reduced protein expression in NK and T cells by up to 95%. The cytotoxicity assays demonstrated that NKG2A silencing effectively enhanced NK and CD8+ T-cell lysis by up to 40% and 15%, respectively. However, lysis of K562 cells which lack human leukocyte antigen-E, the ligand of NKG2A, was associated with an upregulation of the natural cytotoxicity receptor NKp30 in NKG2A-silenced NK cells. Our data suggest that RNAi-mediated silencing of NKG2A in effector cells could improve the efficacy of cell-based immunotherapies but also show that indirect effects of NKG2A knockdown exist that have to be considered when designing therapeutic protocols with genetically engineered NK or T cells.

Proteomic analysis of human NK-92 cells after NK cell-mediated cytotoxicity against K562 cells

To better understand the natural killer (NK) cell cytotoxicity mechanism at the proteome level, we comparatively analyzed the proteome of the human NK-92 cells which participate in NK cell-mediated cytotoxicity assay and that of control cells. Soluble proteins were separated by two-dimensional gel electrophoresis (2-DE), 75 protein spots were found to be reproducibly differentially expressed between control and cytotoxic human NK-92 cells. A total of 60 different proteins were unequivocally identified by MALDI-TOF MS coupled with database interrogation; 37 proteins were up-regulated, whereas 23 proteins were down-regulated. Western blotting analysis of heat shock protein 60 (HSP60) and cathepsin W verified their proteome results. Some of identified proteins are involved in NK-92 cytotoxicity, which is consistent with the literature. In addition, we modeled the pathway networks between differentially expressed proteins and cellular processes of secretion and exocytosis through PathwayStudio software. The results of this study help to provide insight into the molecular mechanism of NK cell cytotoxicity.

Contribution of KIR3DL1/3DS1 to ankylosing spondylitis in human leukocyte antigen-B27 Caucasian populations

Killer cell immunoglobulin-like receptors (KIRs) and human leukocyte antigen (HLA) loci are both highly polymorphic, and some HLA class I molecules bind and trigger cell-surface receptors specified by KIR genes. We examined whether the combination of KIR3DS1/3DL1 genes in concert with HLA-B27 genotypes is associated with susceptibility to ankylosing spondylitis (AS). Two HLA-B27-positive Caucasian populations were selected, one from Spain (71 patients and 105 controls) and another from the Azores (Portugal) (55 patients and 75 controls). All were typed for HLA-B and KIR (3DS1 and 3DL1) genes. Our results show that in addition to B27, the allele 3DS1 is associated with AS compared with B27 controls (p < 0.0001 and p < 0.003 in the Spanish population and Azoreans, respectively). We also observed that the association of KIR3DS1 to AS was found in combination with HLA-B alleles carrying Bw4-I80 in trans position in the Spanish population (30.9% in AS versus 15.2% in B27 controls, p = 0.02, odds ratio (OR) = 2.49) and in Azoreans (27.2% in AS versus 8.7% in B27 controls, p = 0.01, OR = 4.4 in Azoreans). On the other hand, 3DL1 was decreased in patients compared with B27 controls (p < 0.0001 in the Spanish population and p < 0.003 in Azoreans). The presence of this allele in combination with Bw4-I80 had a protective effect against the development of AS in the Spanish population (19.7% in AS, 35.2% in B27 controls; p = 0.03, OR = 0.45). The presence of KIR3DS1 or KIR3DL1 in combination with HLA-B*27s/HLA-B Bw4-I80 genotypes may modulate the development of AS. The susceptibility to AS could be determined by the overall balance of activating and inhibitory composite KIR-HLA genotypes.

Mechanisms of disease: infection and spondyloarthritis

There is compelling evidence that some infections can initiate a chronic nonseptic arthritis. This has proved to be an important area of investigation into gene-environment interactions, particularly since HLA-B27 confers increased susceptibility to reactive arthritis. This research has investigated the microbiology of these events, and the strategies used by pathogens to induce chronic joint inflammation. Insights into the HLA-orchestrated immune response in this context have also shed light on the impact of HLA-B27 on immunity, which might provide insights into the mechanism of other HLA-B27-associated diseases. Despite the genetic link to reactive arthritis, there is no proven relationship between ankylosing spondylitis and an inciting infection. In general, most trials have found antibiotics to be ineffective in modifying the course of spondyloarthritis.

NKG2 receptor-mediated regulation of effector CTL functions in the human tissue microenvironment

NKG2 receptors and their ligands play an essential role in the control of CTL activation in the tissue microenvironment. We discuss the regulation of NKG2 receptor expression by CTL and how uncontrolled activation of NKG2 receptors can lead to organ-specific autoimmune and inflammatory disorders.

Killer cell Ig-like receptor-dependent signaling by Ig-like transcript 2 (ILT2/CD85j/LILRB1/LIR-1)

Inhibitory killer cell Ig-like receptors (KIR) signal by recruitment of the tyrosine phosphatase Src homology region 2 domain-containing phosphatase-1 to ITIM. In the present study, we show that, surprisingly, KIR lacking ITIM are able to signal and inhibit in the human NK cell line NK92, but not in mouse NK cells. Signaling by mutant KIR is weaker than the wild-type receptor, does not require the transmembrane or cytoplasmic tail of KIR, and is blocked by overexpression of a catalytically inactive Src homology region 2 domain-containing phosphatase-1 molecule. We also demonstrate that mutant KIR signaling is blocked by Abs, which disrupt the interaction between KIR and human leukocyte Ag-C or Abs, which block the interaction between Ig-like transcript 2 (ILT2) and the alpha3 domain of HLA class I molecules. Thus, although ILT2 expressed in NK92 is insufficient to signal in response to human leukocyte Ag-C alone, ILT2 can signal in a KIR-dependent manner revealing functional cooperation between receptors encoded by two distinct inhibitory receptor families.

Innate and adaptive immunity: the yin and yang of celiac disease

Celiac disease is a multigenetic complex inflammatory disorder with an autoimmune component, induced by gluten, a protein found in wheat. It is a unique human disease model to dissect the innate and adaptive immune mechanisms underlying T-cell-mediated tissue destruction and the development of T-cell lymphoma in conditions of chronic T-cell activation.

The Src family kinases Hck and Fgr negatively regulate neutrophil and dendritic cell chemokine signaling via PIR-B

In classical descriptions of leukocyte chemokine signaling, Src family kinases are thought to function in a positive fashion by coupling receptor associated Galpha subunits to downstream mitogen activated protein (MAP) kinase activation. However, neutrophils derived from hck-/-fgr-/- mice and dendritic cells (DCs) from fgr-/- animals manifested significantly higher intracellular signaling (Ca2+ flux, MAP kinase activation, actin polymerization) and functional responses (chemotaxis in vitro and migration in vivo) to a number of different chemokines. These kinases may mediate their effect through the inhibitory receptor PIR-B since neutrophils and DCs from pir-b-/- mice were also hyperresponsive to chemokine stimulation. In wild-type (wt) cells dephosphorylation of PIR-B was associated with maximal chemokine signaling, whereas in hck-/-fgr-/- cells PIR-B was unphosphorylated. These data support a model in which the Src family kinases Hck and Fgr function as negative regulators of myeloid cell chemokine signaling by maintaining the tonic phosphorylation of PIR-B.

Exacerbated graft-versus-host disease in Pirb−/− mice

Immune responses are often regulated by opposing receptor pairs that recognize the same ligand but deliver either activating or inhibitory signals. Paired immunoglobulin-like receptors (PIRs) expressed on B cells and myeloid cells comprise a major histocompatibility complex class I recognition system that regulates the responsiveness of these cells. Here, activating PIR-A and inhibitory PIR-B bound various mouse major histocompatibility complex class I (H-2) molecules, and in vitro H-2 tetramer stimulation of PIR-B on B cells or PIR-A on macrophages induced intracellular phosphotyrosine signaling. After transfer of allogeneic splenocytes into PIR-B-deficient mice, the mice showed exacerbated graft-versus-host disease, which was due to augmented activation of recipient dendritic cells with concomitant upregulation of PIR-A and increased interferon-gamma production. PIR-A-induced dendritic cell activation also led to increased proliferation of donor cytotoxic T cells. Thus, PIR-A and PIR-B are counteracting receptors that are essential for successful tissue transplantation and may regulate irrelevant reaction to autologous tissues in a constitutive way in physiological conditions.

Functional involvement of cathepsin W in the cytotoxic activity of NK-92 cells

Human cathepsin W (lymphopain) is a papain-like cysteine protease of unknown function that is specifically expressed in natural killer (NK) cells and to a lesser extent in cytotoxic T cells (CTL). In order to analyze the functional importance of cathepsin W for the cytotoxic process, we investigated NK-92 cells that have an NK cell-like phenotype and express cathepsin W. NK-92 cells possess strong cytotoxic activity against Jurkat and K562 cells. The cytotoxic activity of NK-92 cells against K562 was decreased in the presence of antisense phosphorothioate oligonucleotides against the cathepsin W-cDNA. Western blot analysis showed that the impaired cytotoxic activity of NK-92 cells was accompanied by reduced amounts of cathepsin W in the antisense-treated cells. In addition, co-cultivation experiments between NK-92 and K562 cells revealed a time-dependent decrease of cathepsin W by Western blot and immunofluorescence analysis during the cytotoxic attack, whereas CD56 expression of NK-92 cells was not affected. During cytotoxic attack, cathepsin W was neither targeted to K562 cells or other subcellular compartments, as shown by immunofluorescence analysis. The decrease of cathepsin W protein was associated with stable cathepsin W transcript levels. Control experiments using HT-29 cells, which are resistant against NK-92-mediated cytotoxicity, showed no change of cathepsin W expression, implying that the decrease of cathepsin W in the NK-92/K562 assay is linked to the cytotoxic process. Although the exact function of cathepsin W with respect to its enzymatic activity and its site of action still needs to be elucidated, our data demonstrate for the first time that cathepsin W is important for cellular cytotoxicity mediated by NK cells.

CD8 alpha beta T cells are not essential to the pathogenesis of arthritis or colitis in HLA-B27 transgenic rats

The class I MHC allele HLA-B27 is highly associated with the human spondyloarthropathies, but the basis for this association remains poorly understood. Transgenic rats with high expression of HLA-B27 develop a multisystem inflammatory disease that includes arthritis and colitis. To investigate whether CD8alphabeta T cells are needed in this disease, we depleted these cells in B27 transgenic rats before the onset of disease by adult thymectomy plus short-term anti-CD8alpha mAb treatment. This treatment induced profound, sustained depletion of CD8alphabeta T cells, but failed to suppress either colitis or arthritis. To address the role of CD8alpha(+)beta(-) cells, we studied four additional groups of B27 transgenic rats treated with: 1) continuous anti-CD8alpha mAb, 2) continuous isotype-matched control mAb, 3) the thymectomy/pulse anti-CD8alpha regimen, or 4) no treatment. Arthritis occurred in approximately 40% of each group, but was most significantly reduced in severity in the anti-CD8alpha-treated group. In addition to CD8alphabeta T cells, two sizeable CD8alpha(+)beta(-) non-T cell populations were also reduced by the anti-CD8alpha treatment: 1) NK cells, and 2) a CD4(+)CD8(+)CD11b/c(+)CD161a(+)CD172a(+) monocyte population that became expanded in diseased B27 transgenic rats. These data indicate that HLA-B27-retricted CD8(+) T cells are unlikely to serve as effector cells in the transgenic rat model of HLA-B27-associated disease, in opposition to a commonly invoked hypothesis concerning the role of B27 in the spondyloarthropathies. The data also suggest that one or more populations of CD8alpha(+)beta(-) non-T cells may play a role in the arthritis that occurs in these rats.

Prevalence, clinical relevance and characterization of circulating cytotoxic CD4+CD28- T cells in ankylosing spondylitis

Circulating CD3+CD4+CD28- cells exhibit reduced apoptosis and were found to be more enriched in patients with ankylosing spondylitis than in age-matched healthy control individuals (7.40 +/- 6.6% versus 1.03 +/- 1.0%; P < 0.001). Levels of CD4+CD28- T cells correlate with disease status as measured using a modified metrology score, but they are independent of age and duration of ankylosing spondylitis. CD4+CD28- T cells produce IFN-gamma and perforin, and thus they must be considered proinflammatory and cytotoxic. These T cells share phenotypic and functional properties of natural killer cells, strongly expressing CD57 but lacking the lymphocyte marker CD7. MHC class I recognizing and activating natural killer cell receptors on the surface of CD4+CD28- T cells may be involved in a HLA-B27 mediated co-stimulation of these proinflammatory and cytotoxic cells.