Millipore diffusion chambers allow dissociation of myelin phagocytosis by non-resident cells and of allogenic nerve graft rejection.

Allogenic graft rejection leads to rapid tissue destruction of nerves transplanted directly into a muscle lodge. If the nerves are enclosed in 5.0 micron pore chambers and transplanted into the peritoneal cavity, there is no allogenic graft rejection. The phagocytosis of myelin by invading cells is, however, not disturbed, showing that these cells can distinguish the degenerating myelin from the Schwann cell without being responsive to the Schwann cell's allotype. If the allografts are allowed to predegenerate for 4 wk in 0.22 micron pore chambers which do not admit any cells, there is a striking mitigation of the allogenic graft rejection if the nerves are subsequently released from the chamber. Myelin phagocytosis in such nerves is also reduced. These observations indicate the existence of a hierarchy of cellular recognition mechanisms involved in nerve tissue degradation. Phagocytosis of the myelin sheath by macrophages involves recognition mechanisms which differ from those of the allogenic rejection of the Schwann cell, presumably mediated by T lymphocytes.