The Pathogenesis of HLA-B27 Arthritis: Role of HLA-B27 in Bacterial Defense

Reactive arthritis

Reactive arthritis (ReA) is an immune-mediated seronegative arthritis that belongs to the group of spondyloarthropathies and develops after a gastrointestinal or genitourinary system infection. The condition is considered to be characterized by a triad of symptoms (conjunctivitis, arthritis and urethritis) although a constellation of other manifestations may also be present. ReA is characterized by psoriasiform dermatological manifestations that may resemble those of pustular psoriasis and, similar to guttate psoriasis, is a post-infectious entity. Also, the articular manifestations of the disorder are similar to those of psoriatic arthritis and both conditions show a correlation with HLA-B27. These facts have led several authors to suggest that there is a connection between ReA and psoriasis, listing ReA among the disorders related to psoriasis. However, the pathogenetic mechanism behind the condition is complex and poorly understood. Bacterial antigenicity, the type of host response (i.e. Th1/Th2 imbalance) and various genetic factors (i.e. HLA-B27 etc.) play an important role in the development of the disorder. It is unknown whether all the aforementioned factors are part of a mechanism that could be similar to, or share basic aspects with known psoriasis pathogenesis mechanisms.

Yersinia EnterocoliticaO:3 Isolated from Patients with or without Reactive Arthritis Induces Polyclonal Activation of B Cells and Autoantibody ProductionIn Vivo

The mechanisms by which arthritis-provoking pathogens such as Yersinia enterocolitica interact with the human immune system to produce inflammatory synovitis are not well known. One of the immunomodulating mechanisms used against these pathogens is the polyclonal activation of lymphocytes. In this study, we investigated the extent of the B-lymphocyte activation induced in mice by a strain of Y. enterocolitica O:3 (FCF 526) isolated from a patient with arthritis, and compared it with two other strains, a virulent one (FCF 397[+]) isolated from a patient without arthritis and its plasmidless isogenic pair (FCF397[-]). Also we investigated the production of autoantibodies in mice infected with these different strains. SPF Swiss mice were infected intravenously with a suspension of Y. enterocolitica. Spleen cells were taken on days 7, 14, 21 and 28 after infection and the number of cells secreting nonspecific and specific antibodies of IgG1, IgG2a, IgG2b, IgG3, IgM and IgA isotypes were determined by the ELISPOT technique. The presence of autoantibodies in mouse serum was investigated by the dot-blot assay. The pattern of infection of the three bacterial strains were almost the same. We observed a general increase in the number of nonspecific Ig-secreting cells with all three strains, and the greatest increases observed were in the IgG2a and IgG3 isotypes. Only a small fraction of the immunoglobulins detected were antibacterial, suggesting that the rest resulted from polyclonal B cell activation. The strain isolated from the patient with arthritis (FCF526) induced the greatest production of autoantibodies, coinciding with the period in which the greatest activation of nonspecific B lymphocytes was seen. There were no signs of arthritis or inflammation in the joints of the infected animals. Based on our results, we were unable to determine whether there is an association between the arthritogenic capability of Y. enterocolitica and polyclonal activation of B cells.

Defective Fas ligand-mediated apoptosis predisposes to development of a chronic erosive arthritis subsequent to Mycoplasma pulmonis infection

OBJECTIVE

To determine whether defective T cell apoptosis is associated with the development of a chronic arthritis subsequent to mycoplasma infection, and to determine whether deletion of T cells can prevent the development of this arthritis.

METHODS

B6 wild-type (B6-+/+), B6-lpr/lpr, and B6-gld/gld mice were infected with Mycoplasma pulmonis. The severity of lymphocytic infiltration and joint damage was evaluated, and the degree of recovery of viable mycoplasma from the spleen and joints was determined. Antigen-presenting cells derived from Fas mutant lpr mice (lpr-APC) were transfected ex vivo with an adenovirus (Ad) vector to yield lpr-APC expressing high levels of Fas ligand (lpr-APC-AdFasL), which in turn were transferred intraperitoneally into M pulmonis-infected B6-gld/gld mice. The development of arthritis subsequent to M pulmonis infection and the induction of apoptosis of cells within the synovial tissue and lymph nodes of lpr-APC-AdFasL-treated B6-gld/gld mice were determined.

RESULTS

Infection of B6-lpr/lpr and B6-gld/gld mice with M pulmonis resulted in an acute-phase inflammation of the synovium that later developed into a chronic erosive arthritis. Similar infection of B6-+/+ mice resulted only in an acute joint inflammatory response that resolved. Chronic arthritis in B6-gld/gld mice and B6-lpr/lpr was not due to persistent infection, since there were no differences in the rates of clearance of M pulmonis from the joints of B6-gld/gld or B6-lpr/lpr mice compared with B6-+/+ mice. Treatment of infected B6-gld/gld mice with lpr-APC-AdFasL resulted in a significantly decreased incidence of chronic arthritis that was associated with a decrease in lymph node T cells, but not with apoptosis of synovial T cells or fibroblasts.

CONCLUSION

Defective Fas/FasL-mediated apoptosis of T cells is an important factor that rendered arthritis-resistant B6 mice susceptible to the development of a chronic erosive arthritis subsequent to mycoplasma infection. In vivo lpr-APC-AdFasL cell-gene therapy is a safe and effective method for inhibiting the development of this arthritis.

A molecular insight on the association of HLA-B27 with spondyloarthropathies

This article focuses on molecular studies concerning HLA-B27 and their relevance for its pathogenetic role in spondyloarthropathy. The peptide binding and T-cell antigen presenting properties of HLA-B27 are discussed, mainly in connection with differential subtype association to ankylosing spondylitis. Molecular studies in transgenic rodents are also considered, with an emphasis on their relevance to the various pathogenetic mechanisms. Recent studies on the putative role of HLA-B27 in bacteria-host interactions are also discussed, as they suggest another level of implication of HLA-B27 in disease whose molecular basis is obscure.