Mycoplasma pulmonis arthritis in mice: microbiological and immunological features

Bone and joint disease associated with primary immune deficiencies

Primary immune deficiencies (PIDs) are characterized by functional and/or quantitative abnormalities of one or more immune system components. Several bone and joint abnormalities can occur in patients with PID, with arthritis being the most common. Joint manifestations, of which arthritis is the most common, occur chiefly in humoral PIDs (agammaglobulinemia, common variable immunodeficiency, hyper-IgM syndromes, and IgA deficiency) and occasionally in other PIDs (chronic granulomatous disease and Wiskott-Aldrich syndrome). Monoarthritis or oligoarthritis is the usual pattern, although polyarthritis may occur, occasionally with nodules suggesting rheumatoid arthritis. Arthritis in patients with PID is usually infectious in nature, the most common causative organism being Mycoplasma, followed by Staphylococcus, Streptococcus, and Haemophilus. These bacteria can induce not only synovial infections, but also aseptic arthritogenic inflammatory responses. Arthritis having no demonstrable relation to chronic infection has been reported also and ascribed to dysimmunity-driven mechanisms that exhibit a number of specific features. Bone lesions are far less common and usually due to infections complicating humoral PID. Distinctive bone manifestations occur in a number of rare PIDs (e.g., hyper-IgE syndrome and Di George syndrome) and in syndromes characterized by spondyloepiphyseal dysplasia. Familiarity with PID syndromes both enhances the diagnostic capabilities of physicians and provides insight into the pathophysiology of bone and joint abnormalities associated with immune dysfunction. In children and occasionally in adults, a combination of bone and/or joint manifestations and hypogammaglobulinemia may indicate PID. When there is no evidence of lymphoproliferative disease, infection, or iatrogenic complications, investigations for PID should be obtained. PID-related arthritis is a unique model for studying the pathogenesis of presumably postinfectious arthritis and of inflammatory joint diseases including rheumatoid arthritis.

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.

Immunomodulatory properties of Mycoplasma pulmonis. I. Characterization of the immunomodulatory activity

For many years, it has been recognized that Mycoplasma infection affects the host's immune system in different ways. In this work, experiments were performed to characterize the influence of Mycoplasma pulmonis infection on various immunological parameters and to follow the kinetics of their variations. A Balb/c mouse model was used to assess hematological evaluations, changes in spleen weight, antibody responses against sheep erythrocytes, neutrophil phagocytosis, colloidal carbon clearance, and anti-Mycoplasma antibody responses. At the hematological level, infected animals were found to have significantly increased total lymphocyte and polymorphonuclear leukocyte counts and an augmentation in spleen weight. Seven days after Mycoplasma infection, antibody responses against sheep erythrocytes were considerably diminished, and at days 7 and 14 after infection, phagocytic activity was also reduced. After 1 week of infection, the colloidal carbon clearance pattern was decreased, and during the whole infectious process, anti-Mycoplasma antibody titers were found to be low. Results from this part of research show a persistent infection that does not resolve in a short period, which is associated with a general dysfunction in the immune system and poor immune responses against several different antigens.