Is spondylitis caused by Klebsiella?

The microbiome in spondyloarthritis

A causal link between the wealth of microbes that populate our body surfaces, designated as microbiota, and inflammatory disorders, including ankylosing spondylitis and the related spondyloarthritis (SpA) has been suspected for decades. This specially concerns the gut microbiota that became only recently accessible to thorough description thanks to massive sequencing methods or metagenomics. Here, we review evidences supporting the existence of microbiota imbalance or dysbiosis in the context of SpA. We also discuss currently existing evidences for a causal relationship between such dysbiosis and disease development, as well as putative therapeutic implications.

Molecular mimicry: any role in the pathogenesis of spondyloarthropathies?

Ankylosing spondylitis and reactive arthritis are seronegative spondyloarthropathies, which are strongly associated with HLA-B27. Despite intensive investigation, the basis for this association is not clear. However, in recent years one favored hypothesis to explain this linkage has been that of molecular mimicry, i.e., sharing of linear or conformational epitopes common to microbial antigens and host structures. During the past few years several examples of molecular mimicry between HLA-B27 and microbial antigens have been described. Heat shock proteins, among others, have been considered as target candidates for autoimmune phenomena, because of the high degree of homology between bacterial and mammalian species. Reactive arthritis triggered by Yersinia or Salmonella provides a unique model for studying the pathogenetic mechanisms underlying human inflammatory joint diseases in general, because the arthritogenic microbes are known and well-characterized. We have described two bacterial proteins that share amino acid homology with HLA-B27, namely YadA (Yersinia adhesin) and OmpH, outer surface proteins of Yersinia and Salmonella, respectively. Notably, the area of identity of these amino acid sequences is located in the same place on the HLA-B27 molecule as a hexapeptide identical between Klebsiella nitrogenase and HLA-B27, and a pentapeptide shared by a Shigella flexneri protein and HLA-B27. We have investigated immune responses to a panel of synthetic peptides based on the HLA-B27-homologous portions of pathogen-specific antigens in patients with reactive arthritis and ankylosing spondylitis. One third of the patients have antibodies to the synthetic peptides. However, instead of recognizing the HLA-B27-homologous portion, the antibodies are directed against the flanking sequences of the synthetic peptides. The concept of the role of molecular mimicry between HLA-B27 and microbial antigens in the pathogenesis of spondyloarthropathies is discussed, with a conclusion that no convincing evidence for its significance exists at the present.

Ankylosing spondylitis and HLA-B27: restriction fragment length polymorphism and sequencing of an HLA-B27 allele from a patient with ankylosing spondylitis

Two groups of patients with ankylosing spondylitis (AS) from England and Poland were examined for restriction fragment length polymorphisms (RFLPs) associated with the disease. No preferential association was found between the 9.2 kb PvuII fragment in HLA-B27 positive patients with AS compared with HLA-B27 healthy subjects as had been previously reported. In the English group, however, a 14 kb PvuII fragment was more common in HLA-B27 positive subjects with AS than in normal controls. Also 4.6 and 3.7 kb PvuII fragments were more prevalent in subjects without AS than in the group with AS, but these results were confined to the English group. Furthermore, the sequence of an HLA-B*2705 gene isolated from a patient with AS was examined, and no significant differences were found compared with the sequence isolated from a healthy subject. There do not seem to be significant genetic differences in the coding or in the regulatory region in HLA-B27 alleles, in subjects with or without AS.

Reactive arthritis: the role of bacterial antigens in inflammatory arthritis

For more than 100 years it has been suspected that bacteria or products derived from them are deposited in joints and cause arthritis without suppuration. Over this time a vast amount of evidence, much of which is still unchallenged, has accumulated to demonstrate that whole bacteria and subcellular bacterial elements do pass, under certain circumstances, from sites of mucosal colonization or infection into the circulation and thence into joints. Similarly, experimental studies have demonstrated that the deposition of both inert material and bacterial components within synovium is sometimes, but not always, associated with the development and persistence of synovitis. In human reactive arthritis aseptic synovitis follows localized bacterial infection in the gut or genitourinary tract. A genetic predisposition, associated with the HLA B27 antigen, is recognized, and interaction between class I HLA determinants and bacteria-derived antigens may underlie the development of arthritis. Although much remains to be learned about the dissemination of antigens from the primary site of infection in reactive arthritis, strong evidence implicates the deposition of antigenic elements of Chlamydia, Yersinia, Salmonella and perhaps other micro-organisms within the synovium. Immunological findings support the notion that such antigens are being presented within the joint and participating in the induction and/or maintenance of synovitis. It is not yet clear whether such bacteria are complete or viable or whether persistence at an extra-articular site is important to the persistence of arthritis. The possibility that reactive arthritis, and perhaps other forms of seronegative arthritis also, is caused and perpetuated by bacterial antigens within the joint poses new questions about the role of HLA B27 in pathogenesis. It also raises important and exciting issues regarding treatment. Already, studies of antimicrobial therapy have yielded encouraging initial findings, and it is now possible to design and evaluate therapies aimed at blocking specific antigen recognition within the joint.

Maintenance of multiallelic polymorphism at the MHC region

Models that purport to explain the maintenance of MHC polymorphism must be able to explain a variety of phenomena. (1) The range of MHC allele frequencies at some of the loci is very large, with some alleles quite common and many others rare, while at others the range of allele frequencies is far narrower. (2) MHC alleles and their frequencies often have long persistence times, in some cases tens of millions of years. (3) Random-mating populations appear to be in Hardy-Weinberg equilibrium for MHC. (4) There is no obvious, strong and consistent selection pressure yet detected that acts differentially on different MHC genotypes. (5) Because the allelic composition of the MHC polymorphism does change over evolutionary time, the MHC system must be capable of accommodating new alleles with similar properties without destruction of the equilibria that permit the maintenance of the older alleles. In this review I examined the degree to which a large number of models that have been proposed fit these criteria. These include heterosis, marginal overdominance, conditional heterosis, assortative mating, maternal-fetal incompatibility, molecular mimicry, minority advantage, pathogen adaptation, and optimum allele frequency models. Most of the models do poorly at accounting for a number of the above phenomena. The last class, optimum allele frequency models, have the most satisfactory set of properties. However, optimum allele frequency models require mechanisms that somehow "feed back" from the frequency of an allele in the population to the fitness of an organism carrying that allele. Thus, these models require that MHC polymorphisms be maintained by some type of group selection. Evidence for an against optimum allele frequency selection, and ways in which this type of selection might be detected experimentally, are presented.

Heat-shock proteins as immunogenic bacterial antigens with the potential to induce and regulate autoimmune arthritis

Heat-shock proteins are ubiquitous and surprisingly immunogenic bacterial proteins. Due to their extensive evolutionary conservation, development of immune reactivity directed at hsp is expected to jeopardize the maintenance of tolerance for "self". The experimental model of adjuvant arthritis in rats has been illustrative in this respect. In this model disease is induced by immunization to mycobacteria, and by T-cell cloning it appeared that T cells with specificity for the 180-188 sequence of the mycobacterial hsp65 were capable of both inducing the disease or inducing resistance to the disease. Although the exact molecular mimicry relationship of this 180-186 epitope with the proteoglycan moiety of cartilage remains to be elucidated, the crucial significance of hsp65 immunity has been substantiated further, not only in adjuvant arthritis, but also in other models of experimentally induced arthritis. Development of disease is seen to coincide with development of hsp65 reactivity, and in AA to the 180-186 epitope in particular. There is now experimental evidence that responses to hsp65 are subject to regulatory T-cell control, and that such regulatory control may explain the observations that preimmunization with hsp65 induces protection against subsequent development of arthritis. In human arthritis, responses to hsp65 have been seen to occur at the level of synovial fluid-derived T lymphocytes. Especially, in children with juvenile chronic arthritis such responsiveness was seen to be directed at the endogenous "self" hsp60, as it was also found to be expressed at a raised level in the synovial lining cells. Altogether, both from the experimental models and from the human disease, evidence is being collected for hsp65 as a critical antigen which has, in the experimental models, the potential of inducing protective regulatory T-cell control. AA has now offered us some initial possibilities for exploiting this feature of hsp65 in inducing remission of disease. We may hope that, ultimately, such specific immunological intervention in disease will also become a reality in the management of human autoimmune arthritis. The exploitation of the regulatory control mechanisms that normally contain the dangerously autoimmune reactive elements in the system seems to be most attractive for such a purpose. We should not try to modify the outside non-self; however, we should use our understanding of the mechanisms involved in order to stimulate the immune system of the unfortunate to resume control over the management of responses directed at the endogenous "self". It is possible that further analysis of the role of hsp65 in arthritis will lead to such necessary understanding.

Antibodies to the peptide from the plasmid-coded Yersinia outer membrane protein (YOP1) in patients with ankylosing spondylitis

Seventy-five Norwegian patients with ankylosing spondylitis (AS) were studied for class-specific antibody response against synthetic peptide, P81, representing the sequence of plasmid-coded outer membrane protein of Yersinia (YOP1) containing four amino acid homology (TDRE) with HLA-B27 sequence. Ten (16.7%), five (8.3%) and seven (11.2%) of 60 male AS patients showed elevated anti-YOP1 P81 antibody of IgA, IgG, and IgM class, respectively, whereas for each isotype only one (4%) of 25 healthy male controls was positive. Differences were not observed between female patients and controls. In all isotypes, antibody-positive patients were more frequently found in patients with active disease. The anti-YOP1 P81 antibody levels of the patients were generally not correlated with the antibody levels against the peptide representing the hypervariable region of HLA-B27 (B27 peptide). However, in one patient the antibody was shown to react with both peptides by cross-inhibition analysis. Overall, it appears that any causal relationship between YOP1 and pathogenesis of AS is not strong. Immunogenicity and cross-reactivity of the YOP1 region encompassing the TDRE sequence particularly at the T cell level require further study.

Guilt by association: HLA-B27 and ankylosing spondylitis

The remarkable association between HLA-B27 and ankylosing spondylitis (AS) remains an enigma. While previous reviews have discussed the controversies surrounding the involvement of bacteria in the etiology of this disease and the sequence variability between subtypes of HLA-B27, concepts of disease mechanism remain ill-defined. In this article Richard Benjamin and Peter Parham synthesize new data on the structure and function of HLA class I molecules into possible mechanisms that might underly the pathogenesis of AS.

Demonstration of shared epitopes between bacterial proteins and HLA class-I proteins using monoclonal antibodies

Monoclonal antibodies were used to identify the presence of epitopes on bacterial proteins which are cross-reactive with HLA-B27. Anti-HLA-B27 monoclonals, B27M2 and YE-2 reacted with a major protein of approximately 35 kDa, which was found to be OMPA. On some strains a 19 KDa protein was also seen. Anti-Shigella flexneri monoclonals were also developed which reacted with a 36 kDa protein and a 19 kDa protein. The 36 kDa protein was OMPF. These antibodies also reacted with a synthetic peptide representing amino acids 63-83 of the B*2705 sequence. These results support a potential role for molecular mimicry in the spondyloarthropathies.

Structure of class-I MHC molecules: HLA-B27 and disease

In this introductory article, the structure and function of HLA class-I molecules is discussed. The differences between HLA-B27 and the other class-I molecules are described. It is suggested that HLA-B27 contributes to autoimmune phenomena, but little is known about the actual autoimmune mechanisms that cause the B27-associated disease.

Identification of a 2-Md plasmid from Shigella flexneri associated with reactive arthritis

The development of reactive arthritis, a sterile inflammatory polyarthropathy that primarily affects HLA-B27 positive individuals, has been associated with previous enteric infections caused by various gram-negative bacteria. The possibility that a common bacterial epitope triggers the disease was investigated by screening a panel of documented arthritogenic Shigella strains as well as 2 epidemic-associated nonarthritogenic Shigella controls. A 2-Md plasmid specific to the arthritogenic strains was identified and sequenced. The plasmid encodes a number of small peptides that could be related to the development of reactive arthritis. Within 1 of these is a stretch of 5 consecutive amino acids, inferred from the DNA sequence and contained within an open reading frame, that is homologous to amino acid residues 71-75 of the polymorphic region of the alpha 1 domain of HLA-B27. The data indicate that there is a bacterial plasmid common to arthritogenic Shigella strains that may play a role in triggering reactive arthritis. The finding that this plasmid encodes an epitope shared with HLA-B27 suggests that molecular mimicry may play a role in the induction of this disease.

Cross-reactive epitope with Klebsiella pneumoniae nitrogenase in articular tissue of HLA-B27+ patients with ankylosing spondylitis

Synovial tissues from patients with ankylosing spondylitis or reactive arthritis were examined by an immunoperoxidase technique, using antisera to synthetic peptides representing antigens shared between HLA-B27.1 and Klebsiella pneumoniae nitrogenase. With either antiserum, all HLA-B27+ patients with synovial inflammation showed strong immunoperoxidase staining in synovial lining cells, vascular endothelium, and infiltrating inflammatory cells. These findings indicate that antigens showing cross-reactivity between HLA-B27.1 and Klebsiella nitrogenase epitopes are strongly expressed within inflamed synovial tissues of HLA-B27+ patients.

Molecular mimicry between human leukocyte antigen B27 and Klebsiella. Consequences for spondyloarthropathies

Ankylosing spondylitis and Reiter's syndrome are the two major spondyloarthropathies highly associated with human leukocyte antigen (HLA) B27. Although the development of spondylitis is unclear, it has been hypothesized that HLA-B27 may predispose to spondyloarthropathies via the phenomenon of molecular mimicry. A computer search for homologies between HLA-B27 and microbes revealed a sequence of six consecutive amino acids (glutamine-threonine-aspartic acid-arginine-glutamic acid-aspartic acid) shared by HLA-B27.1 (residues 72 to 77), and Klebsiella pneumoniae nitrogenase (residues 188 to 193). Antibodies raised against a peptide derived from HLA-B27 containing this six-amino-acid sequence cross-reacted with the peptide derived from Klebsiella that contained these six amino acids, and vice-versa. These antibodies also reacted with articular tissues from HLA-B27-positive patients with ankylosing spondylitis. Sera from 53 percent of Reiter's patients and 27 percent of patients with ankylosing spondylitis showed binding to these same peptides. These results suggest that molecular mimicry may have a role in disease development.

Bacterial epitopes involved in the induction of reactive arthritis

A panel of documented arthritogenic Shigella flexneri strains as well as an epidemic-associated non-arthritogenic Shigella sonnei control was used to identify a 2-megadalton plasmid specific to the arthritogenic strains. The plasmid, pHS-2, contains a DNA sequence that encodes a 22-amino acid polypeptide encompassing a pentapeptide homologous to part of the polymorphic region of the alpha-1 domain of HLA-B27. These results suggest that molecular mimicry between arthritogenic bacterial-encoded epitopes and the HLA-B27 molecule may play a role in the development of reactive arthritis.

The role of infectious agents in the spondylarthropathies

The clinical similarities of the spondylarthropathies and their frequent association with both HLA B27 and microbial infections suggest common pathogenetic mechanisms. The latter may include deposition of immune complexes containing bacterial antigens. or cross-reactivity of such antigens with host target tissue or responding cell antigens. Enteric bacteria, chlamydia and mycoplasma are all candidate etiologic agents, but proof is difficult because they are often found as normal flora, although only genetically susceptible individuals may acquire disease, and many patients have been treated with antibiotics before they can be studied. Nonetheless, a role for endogenous bacteria in reactive arthritis at least seems certain, and should stimulate further investigation into similar pathogenetic mechanisms in other chronic arthritides.

Monoclonal antibodies to polysialic acid reveal epitope sharing between invasive pathogenic bacteria, differentiating cells and tumor cells

Monoclonal antibodies (mAb) for rapid diagnosis and detection of invasive bacteria and identification of pathogenic factors in infectious disease are equally important in medical microbiology and clinical pathology and may even provide a breakthrough in basic medical and cell biology research. Such a situation evolved from the application of a unique mAb against the poorly immunogenic homopolymers of alpha 2,8-linked sialic acid of Escherichia coli K1 and meningococci group B capsules which could be derived from immune-hyperreactive NZB-autoimmune mice. The cross-reactivity of this mAb with identical polysialic acid (polySA) units of the neural cell adhesion molecule (N-CAM) revealed antigenic mimicry as the basis for the escape of the above-mentioned bacteria from host immune response and immune defense. The mAb proved to be a specific and sensitive diagnostic reagent as well as a very efficient therapeutic agent in experimental E. coli K1 and meningococcal group B infections in mice. Furthermore, the mAb was found to react exclusively with long-chain polySA units characteristic of the embryonic form of N-CAM. This led to the discovery that the embryonic form of N-CAM is present outside neural tissue in the mesodermally derived kidney where it is specifically expressed during embryonic organ differentiation and reexpressed under conditions of malignant growth in nephroblastoma. Therefore, the embryonic form of N-CAM represents an onco-differentiation antigen in kidney.

The individuality of the immune response

The high degree of polymorphism of the genes controlling the immune system makes immune reactivity of any being very individualized. Self non self recognition, rejection of non-self is the most clear and common expression of this individuality. Moreover antigen experience, chance and even psychological conditions may further affect the immune response characteristics so contributing to enhance the individuality of the "way of reacting" and, therefore, of susceptibility to immune-mediated diseases. In this perspective man can consider himself as a true biological ego.

Infection and arthritis

The categorization in four classes of association between infection and arthritis (namely infective, post-infective, reactive and idiopathic) seems nowadays to be inadequate to cover the extensive field of interactions between infectious agents and host response resulting in arthritis. This paper is a synthetic review of the subject with particular reference to pathogenetic mechanisms in children. An effort has been accomplished, on the basis of the most recent literature, to define the respective roles of the microbial aggression and the host response in a number of conditions: septic arthritis, viral arthritides, Lyme arthritis, rheumatic fever, Reiter's syndrome, ankylosing spondylitis and rheumatoid arthritis.