Lymphocyte and mastocytoma (P815) cell populations incubated with DNP-phosphatidylethanolamine in the form of liposomes displayed cell surface hapten as evidenced by: i) 125I-anti-DNP antibody binding; ii) C-mediated lysis, and iii) K-cell mediated lysis. Under optimal conditions, P815 cells incubated with DNP-liposomes showed a higher DNP density than was obtained by direct surface haptenation with dinitrobenzene sulfonic acid (DNBS). Moreover, the DNP transferred via cell-liposome interactions persisted on the cell surface at least as long as that introduced by DNBS.

Despite ready accessibility to antibody, the cell surface hapten introduced by cell-liposome interaction was not recognized by hapten-specific cytotoxic T cells. Thus, cells bearing liposome-derived DNP- (or TNP-) could not serve as targets for H-2 restricted hapten-specific effector cells; did not competitively inhibit the lysis of DNBS- (or TNBS-) modified cells; and, furthermore, did not stimulate hapten-specific cytotoxic cells in either primary or secondary responses. Interestingly, membrane preparations obtained from TNBS-treated cells did not “trigger” primary or secondary hapten-specific cytotoxic responses, although the same preparations readily stimulated “primed” allogeneic cells.

In contrast to the results obtained with cells bearing lipid-associated hapten, the addition of haptenated (DNP- or TNP-) bovine serum albumin (BSA) to lymphocyte cultures readily stimulated H-2 restricted, hapten-specific, cytotoxic T cell production. Cells incubated with DNP- (or TNP-) BSA for even brief (60 to 90 min) periods became susceptible to attack by syngeneic hapten-specific effector cells and specifically inhibited the lysis of syngeneic cells modified with the appropriate nitrobenzene sulfonic acid.

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