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Skeletal muscle regeneration and Trypanosoma cruzi-induced myositis in rats I.R.S.C. Maldonado1*, M.L Ferreira1, E.R.S. Camargos1, E. Chiari2 and C.R.S. Machado1 1Departament of Morphology and 2Department
of Parasitology, Institute of Biological Sciences, Federal University
of Minas Gerais, Minas Gerais , Brazil Offfprint requests to: Conceição R.S. Machado, Departamento de Morfologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais (UFMG), 31270-901 Belo Horizonte, Minas Gerais, Brazil. Fax: 55 31-3499 2810. e-mail: cmachado@mono.icb.ufmg.br
Summary. Although Chagas' disease is known to provoke severe acute myositis, information on muscle regeneration is missing. The current paper shows that during T. cruzi infection in rats, skeletal muscle parasitism and the consequent inflammatory process are higher in muscle with a high proportion of type-I myofibres (soleus and diaphragm). Immuno-histochemistry showed an acute inflammatory process characterized by ED1+ and ED2+ macrophages, CD8+ lymphocytes, and NK cells. Parasite-nest rupture provoked segmental degeneration of myofibres followed by regeneration. These phenomena were observed at both light and transmission electron microscopy levels. Myofibre regeneration involved activation of satellite cells assessed by the expression of MyoD, a muscle-specific transcription factor. Ultrastructural evidence of fusion of myoblast-like cells with the intact segment of degenerating fibres has been provided. At the chronic phase no signs of fibrosis were found, but sparse and small inflammatory foci were found. Our results argue against the relevant participation of autoimmunity phenomena in both acute and chronic phases and furnish a new view for explaining histopathological findings in human patient muscles. Histol. Histopathol. 19, 85-93 (2004) Key words: Muscle
regeneration, Satellite cells, MyoD expression, Macrophages,
Chagas' disease |