MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-II MOLECULE EXPRESSION ON MUSCLE-CELLS IS REGULATED BY DIFFERENTIATION - IMPLICATIONS FOR THE IMMUNOPATHOGENESIS OF MUSCLE AUTOIMMUNE-DISEASES

Major histocompatibility complex (MHC) class II molecules are expresse d on myoblasts after interferon-gamma (IFN-gamma) treatment, suggestin g a muscle cell involvement in antigen presentation in inflammatory my opathies. However, they were not observed on normal or pathological my ofibers. This discrepancy might be related to different responsiveness of developmentally differentiated muscle cells to IFN-gamma. Myoblast s expressed class II transcripts and proteins after IFN-gamma, while m yotubes and innervated contracting muscle cells did not show staining for class II molecules. At all cell stages no loss of IFN-gamma recept or was detected indicating that myofiber maturation blocks their capac ity to express MHC class II molecules. This suggests that completely d ifferentiated myofibers cannot participate in class II restricted immu nological reactions.