Piecemeal necrosis is due to the immunologic synapse formation and internalization of intact TCR-MHC II complexes by CD4 T cells.

The nature of the immunologic synapse in autoimmune hepatitis is defined. This process involves the T cell receptor (TCR) which binds to the hepatocyte antigen presenting major histocompatibility complex (MHC) on the plasma membrane. This complex is quickly removed from the liver cell and taken into the T cell cytoplasm to be digested by the lysosome. The liver cell is gradually diminished to the point of its total removal by the lymphocytes binding to it.