Inger Gjertsson

Model systems: modeling human staphylococcal arthritis and sepsis in the mouse.

The staphylococci have been recognized as serious pathogens for over a century and are the etiological agent of a variety of diseases ranging from mild cutaneous infections to often fatal forms of septic arthritis, endocarditis, toxic shock syndrome and sepsis. Despite intensive efforts to halt their spread, they remain the most common cause of community- and nosocomially acquired bacteremia. Murine models of Staphylocococus aureus-mediated arthritis and sepsis exist and are being used to gain a better understanding of the host-bacterium relationship as well to develop better methods of prevention and treatment.

Reactive Oxygen Species Produced by the NADPH Oxidase 2 Complex in Monocytes Protect Mice from Bacterial Infections

Chronic granulomatous disease (CGD) is an inherited disorder characterized by recurrent life-threatening bacterial and fungal infections. CGD results from defective production of reactive oxygen species by phagocytes caused by mutations in genes encoding the NADPH oxidase 2 (NOX2) complex subunits. Mice with a spontaneous mutation in Ncf1, which encodes the NCF1 (p47phox) subunit of NOX2, have defective phagocyte NOX2 activity. These mice occasionally develop local spontaneous infections by Staphylococcus xylosus or by the common CGD pathogen Staphylococcus aureus. Ncf1 mutant mice were more susceptible to systemic challenge with these bacteria than were wild-type mice. Transgenic Ncf1 mutant mice harboring the wild-type Ncf1 gene under the human CD68 promoter (MN+ mice) gained the expression of NCF1 and functional NOX2 activity specifically in monocytes/macrophages, although minimal NOX2 activity was also detected in some CD11b+Ly6G+ cells defined as neutrophils. MN+ mice did not develop spontaneous infection and were more resistant to administered staphylococcal infections compared with MN− mice. Most strikingly, MN+ mice survived after being administered Burkholderia cepacia, an opportunistic pathogen in CGD patients, whereas MN− mice died. Thus, monocyte/macrophage expression of functional NCF1 protected against spontaneous and administered bacterial infections.

Interleukin‐10 ameliorates the outcome of Staphylococcus aureus arthritis by promoting bacterial clearance

Staphyllococcus aureus‐induced infections often result in high mortality and permanent joint destruction, despite treatment with antibiotics. IL‐10 is typically regarded as an anti‐inflammatory cytokine because it promotes a T helper cell type 2 response, and subsequently down‐regulates cell mediated immune functions. To investigate the role of IL‐10 in S. aureus‐induced arthritis and sepsis, Balb/c mice, intact or defective with respect to IL‐10 gene were intravenously inoculated with bacteria. IL‐10–/– mice develop a more frequent and destructive arthritis compared to their congeneic controls. The mechanisms regulating such outcome may be due not only to the anti‐inflammatory properties of IL‐10 but also, directly or indirectly, to antibacterial features of this molecule. Indeed, inoculation of staphylococci to IL‐10–/– mice resulted in higher bacterial load in blood and kidneys compared to congeneic controls. Altogether our data indicate that IL‐10 is essential for efficient elimination of bacteria and thereby for protection against septic arthritis.

Are B Lymphocytes of Importance in Severe Staphylococcus aureus Infections

ABSTRACT To investigate the role of B cells in experimental, superantigen-mediated Staphylococcus aureus arthritis and sepsis, we used gene-targeted B-cell-deficient mice. The mice were inoculated intravenously with a toxic shock syndrome toxin 1 (TSST-1)-producing S. aureus strain. The B-cell-deficient and thus agamma-globulinemic mice showed striking similarities to the wild-type control animals with respect to the development of arthritis, the mortality rate, and the rate of bacterial clearance. Surprisingly, we found that the levels of gamma interferon in serum were significantly lower (P < 0.0001) in B-cell-deficient mice than in the controls, possibly due to impaired superantigen presentation and a diminished expression of costimulatory molecules. In contrast, the levels of interleukin-4 (IL-4), IL-6, and IL-10 in serum were equal in both groups. Our findings demonstrate that neither mature B cells nor their products significantly contribute to the course ofS. aureus-induced septic arthritis.

Interleukin-17A during Local and Systemic Staphylococcus aureus-Induced Arthritis in Mice

ABSTRACT Staphylococcus aureus is one of the dominant pathogens that induce septic arthritis in immunocompromised hosts, e.g., patients suffering from rheumatoid arthritis treated with immunosuppressive drugs. S. aureus-induced arthritis leads to severe joint destruction and high mortality despite antibiotic treatment. Recently, interleukin-17A (IL-17A) has been discovered to be an important mediator of aseptic arthritis both in mice and humans, but its function in S. aureus-induced arthritis is largely unknown. Here, we investigated the role of IL-17A in host defense against arthritis following systemic and local S. aureus infection in vivo. IL-17A knockout mice and wild-type mice were inoculated systemically (intravenously) or locally (intra-articularly) with S. aureus. During systemic infection, IL-17A knockout mice lost significantly more weight than the wild-type mice did, but no differences were found in the mortality rate. The absence of IL-17A had no impact on clinical arthritis development but led to increased histopathological erosivity late during systemic S. aureus infection. Bacterial clearance in kidneys was increased in IL-17A knockout mice compared to the level in wild-type mice only 1 day after bacterial inoculation. During systemic S. aureus infection, serum IL-17F protein levels and mRNA levels in the lymph nodes were elevated in the IL-17A knockout mice compared to the level in wild-type mice. In contrast to systemic infection, the IL-17A knockout mice had increased synovitis and erosions and locally decreased clearance of bacteria 3 days after local bacterial inoculation. On the basis of these findings, we suggest that IL-17A is more important in local host defense than in systemic host defense against S. aureus-induced arthritis.

Disease-dependent local IL-10 production ameliorates collagen induced arthritis in mice.

Rheumatoid arthritis (RA) is a chronic destructive autoimmune disease characterised by periods of flare and remission. Today’s treatment is based on continuous immunosuppression irrespective of the patient’s inflammatory status. When the disease is in remission the therapy is withdrawn but withdrawal attempts often results in inflammatory flares, and re-start of the therapy is commenced when the inflammation again is prominent which leads both to suffering and increased risk of tissue destruction. An attractive alternative treatment would provide a disease-regulated therapy that offers increased anti-inflammatory effect during flares and is inactive during periods of remission. To explore this concept we expressed the immunoregulatory cytokine interleukin (IL)-10 gene under the control of an inflammation dependent promoter in a mouse model of RA - collagen type II (CII) induced arthritis (CIA). Haematopoetic stem cells (HSCs) were transduced with lentiviral particles encoding the IL-10 gene (LNT-IL-10), or a green fluorescence protein (GFP) as control gene (LNT-GFP), driven by the inflammation-dependent IL-1/IL-6 promoter. Twelve weeks after transplantation of transduced HSCs into DBA/1 mice, CIA was induced. We found that LNT-IL-10 mice developed a reduced severity of arthritis compared to controls. The LNT-IL-10 mice exhibited both increased mRNA expression levels of IL-10 as well as increased amount of IL-10 produced by B cells and non-B APCs locally in the lymph nodes compared to controls. These findings were accompanied by increased mRNA expression of the IL-10 induced suppressor of cytokine signalling 1 (SOCS1) in lymph nodes and a decrease in the serum protein levels of IL-6. We also found a decrease in both frequency and number of B cells and serum levels of anti-CII antibodies. Thus, inflammation-dependent IL-10 therapy suppresses experimental autoimmune arthritis and is a promising candidate in the development of novel treatments for RA.

Impact of transcription factors AP-1 and NF-κB on the outcome of experimental Staphylococcus aureus arthritis and sepsis

Staphylococcus aureus infection is, despite adequate antibiotic treatment, a disease characterized by high mortality. The bacterium triggers an exaggerated immune response in the host, which on the one hand acts as an efficient defense, but on the other hand gives rise to tissue damage. In this study we have modulated the hosts response to S. aureus by inhibition of nuclear factor kappaB (NF-kappaB) and activator protein-1 (AP-1)-triggered release of pro-inflammatory cytokines and tissue-destructive proteins, respectively. Mice were administered with antisense oligonucleotides (ODN) to the p65 subunit of NF-kappaB and/or a double-stranded oligonucleotide (mCoAP-1) with homology to the murine AP-1 binding site of collagenase IV gene (metalloproteinase-9; MMP-9), solely or in combination with antibiotics. In mice systemically treated with antisense ODN to NF-kappaB p65 alone, the bacterial burden in the kidneys was significantly increased (P = 0.04) The same tendency was seen when mCoAP-1 was administered either alone or in combination with antibiotics. We also found significantly (P = 0.04) elevated levels of IL-6 in p65 antisense treated mice. Surprisingly, this p65 antisense therapy approach, which has turned out to be highly efficient in amelioration of aseptic arthritis and colitis, failed to change the clinical course of either septic arthritis or sepsis. We suggest that interaction with transcription factors leads to increased bacterial burden in vivo, abrogating the potential benefits of the anti-inflammatory properties exerted by these compounds.

Antibiotic-killed Staphylococcus aureus induces destructive arthritis in mice.

Permanent reduction in joint function is a severe postinfectious complication in patients with Staphylococcus aureus septic arthritis. We undertook this study to determine whether this reduction in joint function might be caused by persistent joint inflammation after the adequate eradication of bacteria by antibiotics.

Tolerance Induction Using Lentiviral Gene Delivery Delays Onset and Severity of Collagen II Arthritis

The treatment of rheumatoid arthritis remains suboptimal; thus there is considerable interest in the development of strategies that mediate tolerance to autoantigens. Using lentiviral gene transfer in vivo, we expressed the immunodominant epitope of collagen type II (CII) on major histocompatibility complex class II molecules (MHC II) in a mouse model of destructive arthritis. A sequence corresponding to amino acids 259-270 of CII was fused into the class II-associated invariant chain peptide (CLIP) position of the invariant chain to achieve efficient binding to MHC II. Transduction of cloned cells and primary antigen-presenting cells (APCs) in vitro demonstrated successful presentation of the peptide on MHC II, and a physiological glycosylation pattern. Compared with controls, mice intravenously injected with lentiviral vectors encoding this epitope displayed significantly less frequent, less severe, and less destructive arthritis, decreased lymphocyte proliferation in response to restimulation with CII, and lower CII-specific antibody levels. This was associated with an increased production of transforming growth factor-beta (TGF-beta) in vitro. We suggest that overexpression of the immunodominant CII epitope on MHC II induces T cell production of TGF-beta and leads to inhibition of arthritis by means of both antigen-specific and bystander mechanisms. Thus, antigen-specific tolerance induction using lentiviral gene delivery can ameliorate arthritis.

Disease-regulated local IL-10 gene therapy diminishes synovitis and cartilage proteoglycan depletion in experimental arthritis

Objectives Rheumatoid arthritis is a chronic destructive autoimmune disease, but the course is unpredictable in individual patients. An attractive treatment would provide a disease-regulated therapy that offers personalised drug delivery. Therefore, we expressed the anti-inflammatory interleukin-10 (IL-10) gene under the control of inflammation-dependent promoters in a mouse model of arthritis. Methods Proximal promoters of S100a8, Cxcl1, Mmp13, Saa3, IL-1b and Tsg6 were selected by whole-genome expression analysis of inflamed synovial tissues from arthritic mice. Mice were injected intraarticularly in knee joints with lentiviral vectors expressing a luciferase reporter or the therapeutic protein IL-10 under control of the Saa3 or Mmp13 promoter. After 4 days, arthritis was induced by intraarticular injection of streptococcal cell walls (SCW). At different time points after arthritis induction, in vivo bioluminescent imaging was performed and knee joints were dissected for histological and RNA analysis. Results The disease-regulated promoter-luciferase reporter constructs showed different activation profiles during the course of the disease. The Saa3 and Mmp13 promoters were significantly induced at day 1 or day 4 after arthritis induction respectively and selected for further research. Overexpression of IL-10 using these two disease-inducible promoters resulted in less synovitis and markedly diminished cartilage proteoglycan depletion and in upregulation of IL-1Ra and SOCS3 gene expression. Conclusions Our study shows that promoters of genes that are expressed locally during arthritis can be candidates for disease-regulated overexpression of biologics into arthritic joints, as shown for IL-10 in SCW arthritis. The disease-inducible approach might be promising for future tailor-made local gene therapy in arthritis.