Covariation of MHC class I and CD163 positive macrophages in skeletal muscle tissue of polymyositis and dermatomyositis patients after treatment with high-dose intravenous immunoglobulin (IVIg)

Background

Polymyositis (PM) and dermatomyositis (DM) are characterised by symmetrical muscle weakness, inflammatory infiltrates in skeletal muscle tissue and skin rash (DM).

Objective

Our aim was to investigate the effects of high-dose intravenous immunoglobulin (IVIg) treatment of PM/DM patients on expression of various immunological markers in skeletal muscle tissue, e.g. major histocompatibility complex (MHC) class I and macrophages; on clinical signs; and on muscle status.

Methods

Six PM and four DM patients were treated intravenously with high-dose IVIg. Skeletal muscle biopsies were collected from these patients on three occasions: before treatment, and 24–48 hours and 3 months after treatment. Consecutive sections immunohistochemically stained for HLA-ABC and CD163 were analysed both manually by conventional microscope and by computerized image analysis. The percentage of positively stained areas and the number of cells per mm² were assessed.

Results

The skeletal muscle tissue of IVIg-treated PM/DM patients revealed a heterogeneous change and covariation in expression of MHC class I and macrophages. Correlations with clinical parameters and muscle function will be determined.

Conclusions

IVIg treatment affects the expression of MHC class I and CD163 positive macrophages in skeletal muscle tissue of PM/DM patients in a heterogenous and covarying fashion.