Résumé :
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Communication n° 725. Introduction : Polymyositis (PM) is characterised by a proximal muscle weakness and a muscular infiltrate made by macrophages and cytotoxic CD8+ T lymphocytes. Without treatment mortality is up to 70 percent. The basis of treatment is corticosteroid Æ immunosuppressive drugs. The obligatory and often severe side effects of these drugs, prompt us to propose alternative treatments that should be first tested in preclinical model. No animal model standardised, reproducible and well characterised is available to date. The most resembling is the model of experimental autoimmune myositis by intramuscular injection of myosin or C-protein in Lewis rat. Furthermore, immunoregulatory CD4+CD25+ T cells (Treg) have been rediscovered as a pivotal cell population in the control of autoimmunity, but again, to date, nothing is known between PM and Treg. Objectives : To develop one PM animal model in mouse Balb/c (easier to manipulate and with more biotechnological tools developed than in rat) by multiple subcutaneous immunisations with syngenic myosin in presence of complete Freund adjuvant and after Treg depletion. Methods : Mice are subcutaneous immunized 1, 2, 3 or 4 times with 1 mg skeletal myosin at a dose of 100 mg/ml emulsified with an equal volume of CFA on a weekly base. At the same time, 500 ng pertussis toxin in 200µl saline is injected intraperitoneally. Two weeks after the last immunization, muscle blocks are taken for histology. At different time point before the first immunization (1 day) and after (1, 7, 14 days) Treg cells is depleted in some. Results : After immunization, 100% injected mice develop specific intramuscular infiltration, with necrotic fibers and endomysial inflammatory cells. Immunohistochemical analysis show that macrophage cells (CD11b+) are mainly located in the endomysium and connective tissue and some infiltrated muscle fibers. This infiltrate is also composed by CD4+ and CD8+ cells, without any B220+ cells (B lymphocytes). Histological quantitative analysis of the infiltrates suggests that when Treg cells are depleted, myosin immunized mice have more severe inflammatory infiltrates compared to the non depleted ones. Conclusions : We can produce consistent and reproducible EAM disease in BALB/c mice by immunization with mouse BALB/c myosin. The histological Treg depletion effect is a first encouraging result regarding the therapeutic approach of the use of Treg in controlling the maintenance of peripheral tolerance and in the prevention of autoimmunity.
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