The contribution of exogenous cells to regenerating skeletal muscle: an isoenzyme study of muscle allografts in mice.

A sequential study of 180 allografts of minced skeletal muscle has been made in mice, in 124 of which tolerance was induced. The host/donor composition of grafts was assessed in terms of their content of isoenzymes of glucose-6-phosphate isomerase characteristic of host and donor strains. From 0-5 days implanted muscle fibre fragments uniformly underwent degeneration. New myotubes appeared at day 5. Both host and donor isoenzyme were found during this period. In "non-tolerant" hosts, grafts were rejected at 8-12 days, after which only host isoenzyme was found and the graft site usually lacked muscle, consisting of fibrofatty connective tissue. In the few instances where muscle was found in such grafts, this was necessarily formed from host precursor cells which had migrated into the graft site. In "tolerant" hosts, grafts contained up to 80 per cent. of the muscle and usually yielded both host and donor isoenzyme. Where "hybrid" isoenzyme was found, it was probable that host muscle precursor-cells had entered grafts and fused with donor muscle.