Enhancement of the recognition by cytotoxic T lymphocytes (CTL) of target membrane antigens after fusion with whole cells.

Plasma membrane vesicles (R4-PM) prepared from mouse lymphoma cells (RDM4,H2k) were employed to investigate requirements for recognition of target cell membranes by allogeneic cytotoxic T lymphocytes (CTL). Using immunofluorescent staining and fluorescence microscopy, the R4-PM were tested for binding to CTL and were found to bind to these effector cells in a specific manner. However, this binding was very inefficient compared to the binding of whole RDM4 cells to CTL. The R4-PM were then attached to P388D1 cells (H-2d) in the presence of wheat germ agglutinin and polyethylene glycol (PEG), both under conditions which promote membrane fusion (40% PEG) and under conditions which do not (10% PEG). About 1 cell equivalent R4-PM becomes associated per P388D1 cell in both situations. In the cytotoxicity assays that were carried out, the P388D1 cells which had R4-PM attached under fusion conditions were lysed by CTL directed against H2k in a specific manner, while the P388D1 cells which had R4-PM attached under nonfusion conditions were not lysed above background levels by these CTL. These results suggest that recognition of target cells by allogeneic CTL such that lysis occurs requires more than presentation of the alloantigens as they are expressed in plasma membrane vesicles. However, fusion of these vesicles back into living cells apparently enhances the ability of the alloantigens to be recognized.