Passive transfer of tritiated thymidine labeled lymphoid cells sensitized to homologous tissues into non-sensitized isologous hosts resulted in accelerated rejection of homologous skin grafts in the recipients. Despite 33 per cent label of the suspension, only rare labeled sensitized lymphoid cells could be found at the site of rejection.
Passive transfer of sensitized lymphoid cells in millipore chambers implanted subcutaneously or intraperitoneally in non-sensitized isologous hosts resulted in accelerated homograft rejection in the recipients. Transfer of transplantation immunity could not be accomplished with serum from sensitized hosts.
The rejection of homologous tissues without the physical presence of the sensitized cell at the graft site suggested that a humoral agent produced by the cell was capable of rejecting the homograft.