Although immunohistochemistry on muscle biopsies is widely used scientifically and clinically, information is limited regarding the expression in normal healthy subjects. In the present study we investigated the expression of relevant immune markers in a large material (n=58) of healthy subjects and compared with the expression in morphologically normal muscle biopsies (n=46) obtained from clinical routine. As a reference of inflammation, muscle biopsies from idiopathic inflammatmy myopathies (IIM) were used (n=22).
We found that the expression in healthy subjects was not significantly different from that in morphologically normal biopsies, although a few individuals with minimal morphological aberrations also showed higher expression of immune markers. The IIM group showed significantly higher expression of all markers. In brief, major histocompatibility complex (MHC) class I was nmmally not, or very weakly, expressed on muscle fibres, MHC class II was not expressed on capillary endothelial cells, whereas intercellular adhesion molecule (ICAM)-1 was constitutively expressed to a ce1tain degree on capillmy endothelial cells. The complement activation marker membrane attack complex (MAC) was merely absent in nonnal biopsies. Neonatal myosin heavy chain was normally present only in a very few regenerating fibres. A constructed grading scale was found useful, based on normal occun·ence as well as intensity and distribution of expression.
In conclusion we demonstrate the nmmal expression of MHC class I, MHC class II, ICAM-1, MAC and neonatal myosin as found in healthy subjects. The expression was similar in morphologically completely normal muscle biopsies obtained from clinical routine, justifyhtg the use of such biopsies as normal reference. Some caution is warranted for using biopsies with minimal morphological changes, since these showed increased expression of some inflammatory markers.