The role of infection in the pathogenesis of spondyloarthropathies with special reference to human leukocyte antigen-B27

Phosphorylation of STAT-1 serine 727 is prolonged in HLA-B27-expressing human monocytic cells

A tissue antigen, HLA-B27, is strongly associated with a group of rheumatic diseases called spondyloarthritides. Despite the intensive research, the exact role of HLA-B27 in the pathogenesis of these diseases is still unclear. Here we studied whether HLA-B27 modulates the phosphorylation of signal transducer and activator of transcription 1 (STAT-1) serine 727 residue and the localization of STAT-1 in Salmonella-infected human monocytic cells. In addition, we studied the role of signaling molecule double-stranded RNA activated protein kinase (PKR) in these modulatory effects. U937 human monocytic cell transfectants stably expressing wild type HLA-B27 or mutated HLA-B27 heavy chains with amino acid substitutions in the B pocket were prepared. The PMA-differentiated cells were infected with S. enteritidis. Western blotting was used to detect the phosphorylation of STAT-1, and to visualize the localization of STAT-1 in the cells confocal microscopy was used. Specific inhibitors were employed to study the role of PKR in STAT-1 phosphorylation. We discovered that the phosphorylation of STAT-1 serine 727 is prolonged in cells expressing misfolding forms of HLA-B27 after S. enteritidis infection, whereas in mock cells and in cells expressing mutated, non-misfolding HLA-B27 the phosphorylation of serine 727 is transient. Interestingly, STAT-1 serine 727 phosphorylation is partly dependent on PKR. In addition, more STAT-1 is localized in the nucleus of HLA-B27-expressing cells, even before an external trigger, when compared to mock cells. In conclusion, our results show that the phosphorylation of STAT-1 serine 727 residue is prolonged in HLA-B27-expressing monocyte-macrophage U937 cells after bacterial infection. This is of interest since the phosphorylation of serine 727 on STAT-1 is suggested to contribute to macrophage activation and promote inflammatory responses. Therefore, our results provide a mechanism which explains how the expression of an HLA-B27 molecule can impact the course of Salmonella infection and reactive arthritis.

Helicobacter pylori: an underestimated factor in acute anterior uveitis and spondyloarthropathies?

Acute anterior uveitis (AAU) is the most common form of intraocular inflammation, but its aetiology is still unclear. Fifty percent of AAU patients are HLA-B27-positive, and half of these also have spondyloarthropathies (SpA). Numerous serological studies have shown elevated levels of serum antibodies to various Gram-negative bacteria in HLA-B27-positive AAU and SpA patients. Antigenic similarities between these bacteria and host components (HLA-B27) have already been shown. Still, the mechanism underlying these diseases has not been clarified. Among the Gram-negative bacteria, Helicobacter pylori has not been screened in AAU patients. The purpose of our study was to see if this common human pathogen somehow interferes with AAU. In addition Chlamydia trachomatis, Yersinia enterocolitica 03 and 09, Salmonella sp. and Proteus OX19 were also examined. A total of 60 patients consisting of 4 groups (15 patients with AAU, 15 with SpA, 15 with AAU+SpA and 15 healthy control persons) were examined. A high percentage of the serological results of all investigated bacteria was positive: 80% in the AAU, 93.3% in the SpA and 100% in the AAU+SpA group, while it amounted to 66.7% in the control group (p < 0.05). H. pylori showed the highest percentage of positivity in all 3 patient groups (66.7% in the AAU, 73.3% in the SpA and 80% in the AAU+SpA group). In contrast, 26.7% of the controls were anti-H.-pylori-positive, thus showing a statistically significant difference between the patients and the control group (p < 0.05). HLA-B27/B7-CREG positivity was detected in 53.3% of the AAU, 66.7% of the SpA and 93.3% of the AAU+SpA patients and in none of the controls. Our results suggest that H. pylori might be a candidate participating in the development of AAU and SpA. They also support the theory of genetic (HLA-B27) and exogenous factors (Gram-negative bacteria) as probable background of these diseases.

Management of reactive arthritis

Reactive arthritis (ReA) is an aseptic form of articular inflammation induced by infections mainly localised in the gastrointestinal (enteroarthritis) or urogenital (uroarthritis) tracts. The bacteria principally involved as causative agents are Chlamydia, Salmonella, Shigella, Campylobacter and Yersinia. The clinical picture is usually characterised by a mono-oligoarthritis of the lower limbs. Axial involvement is possible and extra-articular manifestations such as enthesitis, tenosynovitis, bursitis and dactylitis are frequent. NSAIDs and sulfasalazine are still the drugs most commonly used in the treatment of ReA. Steroids are administered when inflammatory symptoms are resistant to NSAIDs. Experiences with other DMARDs (disease modifying antirheumatic drugs) such as azathioprine, methotrexate and cyclosporin, have been sporadically reported and they can be employed in patients that are unresponsive to the more usual medicaments. The intake of antibacterials (tetracyclines) may be useful in uroarthritis but have not been so successful in enteroarthrits. In more aggressive cases, or when ReA evolves towards ankylosing spondylitis, TNF-alpha blockers could represent an effective choice.

Major histocompatibility complex class I peptide presentation after Salmonella enterica serovar typhimurium infection assessed via stable isotope tagging of the B27-presented peptide repertoire

Reactive arthritis (ReA) induced by infection with several gram-negative bacteria is strongly associated with expression of the major histocompatibility complex class I molecule HLA-B27. It is thought that due to the intracellular lifestyle of ReA-inducing bacteria, bacterial fragments can be presented by HLA-B27. Cytotoxic T cells recognizing such bacterial peptides or other induced host peptides could cross-react with self peptides presented in the joints, giving rise to disease. Studies to analyze the B27 peptide repertoire in relation to infection were severely hampered, as complex peptide profiles obtained from separate infected and noninfected cell preparations had to be compared. For this study, we applied a new approach to examine the effect of Salmonella enterica serovar Typhimurium infection on the B27 peptide repertoire presented by the HLA-B*2704 subtype associated with disease. Firstly, we showed that both host cell and S. enterica serovar Typhimurium proteins can be tagged metabolically with stable-isotope-labeled arginine. We then designed experiments so that either the tagged endogenous or tagged bacterial B*2704-presented peptide repertoires from infected cells could be analyzed by mass spectrometry from single peptide preparations that included uninfected controls. Using this new approach, we found no evidence for significant changes in endogenous B*2704 peptide presentation after infection or for any S. enterica serovar Typhimurium-derived B27-bound peptide. In conclusion, the hypothesis that S. enterica serovar Typhimurium induces changes in B27 peptide presentation could not be supported.

Enhanced intracellular replication of Salmonella enteritidis in HLA-B27-expressing human monocytic cells: dependency on glutamic acid at position 45 in the B pocket of HLA-B27

OBJECTIVE

To reveal the cause of the impaired elimination of Salmonella enteritidis in HLA-B27-transfected human monocytic cells and to study whether the B pocket of HLA-B27 contributes to these modulatory effects.

METHODS

Stable U937 cell transfectants expressing HLA-A2, B27, or different forms of B27 with amino acid substitutions in the B pocket were prepared. Mock-transfected cells were prepared using the antibiotic resistance vector (pSV2neo) alone. Cells were differentiated, infected with S enteritidis, and the number of live intracellular S enteritidis organisms was determined using the colony-forming unit method. To visualize intracellular S enteritidis, the bacteria were transformed with green fluorescent protein (GFP), and studied by confocal microscopy.

RESULTS

Cells expressing wild-type HLA-B27 were more permissive of intracellular replication of S enteritidis compared with mock-transfected or A2-transfected controls. Cells expressing B27 with an altered B pocket composition having either 6 amino acid substitutions (B27.A2B; substitutions H9F, T24A, E45M, I66K, C67V, and K70H) or a single substitution (B27.E45M) were no longer permissive of S enteritidis replication. In contrast, cells expressing B27 with the single substitution of F for H at position 9 (B27.H9F) retained their permissiveness. Studies using GFP-transformed S enteritidis confirmed that the increase in the amount of intracellular bacteria in B27-expressing cells was due to replication of the bacteria.

CONCLUSION

Our data indicate that HLA-B27 expression modulates the host-microbe interaction that results in an impaired capacity of monocytes to resist intracellular replication of S enteritidis. The phenotype is dependent on glutamic acid at position 45 in the B pocket and, thus, may be due to properties of the B27 heavy chain that are related to this residue. The ability of HLA-B27 to confer susceptibility to Salmonella-triggered reactive arthritis may occur, at least in part, through these modulatory effects.