NERVE-EVOKED ELECTRICAL-ACTIVITY REGULATES MOLECULES AND CELLS WITH IMMUNOLOGICAL FUNCTION IN RAT MUSCLE-TISSUE

Molecules coded by the major histocompatibility complex (MHC) are pres ent on cell surfaces in most tissues, with the cells of the central ne rvous system and skeletal muscle as prominent exceptions. We show here that when rat skeletal muscles are rendered inactive by nerve impulse block, expression of MHC class I molecules occurs on the muscle fibre s. In addition, the number of cells expressing MHC class II molecules in the muscle interstitium is increased by a factor of three after 2 w eeks of impulse blockade. Similar effects obtained by denervation can be counteracted by direct electrical stimulation. Interferon-gamma-lik e immunoreactivity accumulates in inactive muscle fibres, and interfer on-gamma or a related cytokine could be a link between inactivity and MHC upregulation. These findings suggest that nerve-evoked muscle acti vity influences not only the phenotype of the muscle cells themselves, but also processes in the interstitium that may increase the immunore activity of inactive muscle tissue.