Large agranular lymphocytes: early non-specific effector cells in allograft rejection in the mouse.

The cytolytic reactivity and ultrastructure of centrally-reactive and allograft-infiltrating lymphocyte populations was investigated in a murine peritoneal allograft system. Animals sensitized with a single intraperitoneal dose of allogeneic L929 fibroblasts generated a population of splenic cytolytic T cells maximally reactive 10 days after immunization. Sensitized splenic lymphocytes, isolated by immunoadsorption on L929 monolayers, were ultrastructurally classified as mature small lymphocytes. At the graft site, cytolytic non-T lymphoid cells displaying the ability to kill K562 target cells, were demonstrable between 4 and 6 days after sensitization. Six-day peritoneal lymphocyte populations were found to contain both cytolytic T cells (L929 killers) and highly reactive K562 killers. Immunoadsorption and cold target competition studies indicated that the K562 killer cells were able to recognize both K562 and L929 targets. K562 target-binding cells appeared to be ultrastructurally immature and were designated 'large agranular lymphocytes'. The role of cytolytic non-T cells in rejecting allografts is discussed.