Histological pictures of muscles and an evaluation of cellular infiltrations in human polymyositis/dermatomyositis, as compared to the findings in experimental Guinea pig myositis.

We tested whether intramuscular injections of dermatomyositis (DM) patients' sera into guinea pig muscles can be used to transfer myositic alterations to these animals. Additionally, similar tests were performed using neoplastic patients' sera and sera from non-neoplastic, non-myositic patients. The DM patients' sera induced idiopathic inflammatory myopathy (IIM) type histological changes in muscle fibres in guinea pig quadriceps muscles, which were especially evident 72 h after sera injections. Immunohistochemical stainings of myositic guinea pig muscles were done for guinea pig pan-T-cells, monocytes/macrophages, the neuronal marker-protein gene product 9.5 (PGP 9.5) and protein S-100. Our studies proved that the factor(s) responsible for the appearance of characteristic alterations in diseased muscles during the course of DM is/are present in patient sera.