Adoptive transfer of alloimmune memory in the solitary tunicate, Styela plicata

The role of hemocytes in histocompatibility responses of the tunicate, Styela plicata, was tested by adoptive transfer. Hemocytes were transferred to naive hosts from compatible individuals that had been presensitized to allogeneic tissue. Forty-four percent of the hosts that received presensitized hemocytes were capable of eliminating subsequent allografts more rapidly than control tunicates injected with saline, plasma, or hemocytes that had not been sensitized to the original graft donor. This adoptive transfer of alloimmune memory was specific to the presensitizing allogeneic tissue type. The transfer of hemocyte populations enriched in lymphocyte-like cells by density gradient centrifugation also specifically enhanced alloreactivity. Hemocyte fractions depleted of lymphocyte-like cells were incapable of inducing alloimmune memory. These data confirm that allograft rejection in S. plicata is a cell-mediated response involving lymphocyte-like cells.