Mouse splenic lymphocytes and lymphoid tumor cells were modified with the trinitrophenyl (TNP) group either by treatment with trinitrobenzene sulfonate (TNBS) (which covalently modifies cell surface proteins) or with TNP stearoyl dextran (TSD) (which binds to the cell by noncovalent forces). These cell preparations were compared for their ability to: (a) sensitive syngeneic splenic lymphocytes leading to the generation of cytotoxic effector cells; (b) serve as lysable targets in a 4-h(51)Cr- release assay for effector cells generated in (a); and (c) act as blocking cells in the lysis of TNBS-medified targets lysed by TNP self effector cells generated in (a). In none of these three experimental systems did TSD-medified syngeneic spleen or H-2-matched tumor cells act either as a sensitizing immunogen or as a target antigen, despite the demonstration that quantitatively equivalent mounts of TNP were exposed on the cell surface in the TNBS- and TSD-modified cells. In contrast, TNBS-modified spleen cells sensitized syngeneic lymphocytes to generate effectors against TNBS-modified syageneic targets. Furthermore, TNBS- modified, H-2-matched cells served as specific lysable targets and as inhibiting cells for such effectors. These results indicate that the manner in which TNP is associated with the cell surface is important in the immunogenicity and antigenicity of hapten-modified syngeneic stimulating cells in generating H-2-associated cell-mediated lympholysis (CML) reactions. These findings raise the possibility that a covalent or at least a stable linkage with cell surface proteins (possibly H-2- controlled products) is important for immunological function. Furthermore, these observations do not favor the dual receptor model for H-2-restricted syngeneic CML if it is assumed in such a model that one receptor is specific for the TNP moiety and the second for unmodified self major histocompatibility products.

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