PubMed1979
Exogenous lipid analogues can be incorporated into purified plasma membranes of EL4 tumor cells. When EL4 membranes are incubated with sonicated lipid vesicles containing spin-labeled phosphatidylcholine and then purified, they exhibit paramagnetic resonance spectra characteristic of spin labels dilutely dispersed in the lipid bilayer. Also, when EL4 membranes are incubated with vesicles of fluorescent lipid (N-4-nitrobenzo-2-oxa-1,3-diazole phosphatidylethanolamine), the fluorescence intensity of the mixture gradually increases and the labeled membranes are strongly fluorescent under a microscope, whereas the original lipid vesicles are much less fluorescent because of self-quenching at the high relative concentration of the fluorophore in the vesicles (33%, wt/wt). Thus, lipid analogues can be integrated into the bilayers of EL4 plasma membranes. The ability of the EL4 membranes containing trinitrophenyl phosphatidylethanolamine to induce a secondary proliferation of C57BL/6 mouse spleen lymphocytes primarily stimulated by trinitrophenyl-modified autologous cells was investigated. Although trinitrophenyl-modified plasma membranes as well as trinitrophenyl-modified lymphocytes or EL4 cells caused a specific, H-2 restricted response, membranes containing trinitrophenyl phosphatidylethanolamine did not induce a secondary proliferative response. Because of the strong likelihood that all three lipid analogues mentioned above are similar to one another in having a high lateral mobility and in not being strongly associated with H-2 cell-surface molecules, these results can be viewed, with caution, as being consistent with a "modified self" model rather than a dual recognition model for H-2 restriction in the cell-mediated immune response to chemically modified syngeneic cells.