OBJECTIVETo observe the time course of interleukin (IL)-21 and related cytokines expression in rats with experimental autoimmune myocarditis (EAM).

METHODSAntigen was prepared with an emulsion of porcine cardiac myosin in complete Freund's adjuvant, plus Mycobacterium tuberculosis H37Ra strain. EAM model was made by hypodermic injection of myosin in hind legs of Lewis rats.mRNA expression of IL-21 and related cytokines (IL-21R, IL-17, TGF-β, IL-6) in different tissues (heart, liver, spleen, kidney) were determined at 2 weeks after immunization by RT-PCR and quantitative real-time RT-PCR. Furthermore, the time course of IL-21 and related cytokines expression in the acute phase of EAM (2 w, 3 w, 4 w) was determined by quantitative real-time RT-PCR, and IL-21, IL-17 protein expression was determined by Western blot and ELISA. The location of IL-21R was examined by immunohistochemistry at 2 w after immunization.

RESULTSHistopathology examination evidenced abundant mononuclear cells in the myocardium of 2 weeks EAM rats. Fibrosis and multinucleated giant cells were observed in the myocardium of 3 weeks EAM rats. Inflammation was reduced and large amount of fibrosis could be found in 4 weeks EAM rats. The heart weight/body weight ratio in normal, EAM 2 w, 3 w, 4 w group was (3.011 ± 0.117) mg/g, (4.736 ± 1.279) mg/g, (7.200 ± 0.308) mg/g and (4.622 ± 0.978) mg/g respectively. IL-21 mainly expressed in heart and spleen, IL-21R, IL-17, TGF-β mainly expressed in spleen, and IL-17, IL-6 mainly expressed in heart of EAM rats. IL-21R mainly distributed in cardiomyocytes of 2 weeks EAM rats. In line with pathological EAM course, the expression of IL-21 and related cytokines peaked at 2 weeks and then returned to normal at 4 weeks after immunization.

CONCLUSIONIL-21 and related cytokines were involved in the pathological process of EAM, upregulated IL-21 expression might promote Th17 cell differentiation and enhance Th17 cell secretion.