Figure 4.
Cell activation per se does not induce presentation of the IEd-restricted epitope. (a) FcγRIIb2- and FcγRII–ic-γ chimera–expressing cells were incubated for 24 h with OVA–anti-OVA immune complexes. The cells were then incubated with increasing concentrations of 12–26 CI λ repressor peptide and the T cell hybridomas specific for the dominant (IAd 12–26) or cryptic (IEd 12–26) epitopes. The secretion of IL-2 in the cell culture supernatants was measured. Activation of FcγRII– icγ chimera–expressing cells with IC did not modify the efficiency of presentation of the 12–26 peptide. Similar results were obtained in three independent experiments. (b) Cell activation through FcγRII–icγ chimeras does not induce the presentation of the cryptic epitope after antigen internalization by fluid phase uptake. FcγRII–icγ–expressing cells were incubated overnight in the presence of 30 μg/ml CI λ repressor, with or without irrelevant OVA–anti-OVA immune complexes, in order to engage FcγRII–icγ chimeric receptors. The cells were then fixed and reincubated overnight with T cell hybridomas specific for the dominant or the cryptic epitopes. Engagement of FcγRII–icγ chimeric receptors did not induce the presentation of the IEd-restricted cryptic epitope. (c) Cell activation through surface IgG does not induce the presentation of the CI λ repressor cryptic epitope after immune complexes internalization through FcγRIIb2. Cells expressing FcγRIIb2 were incubated in the continuous presence of CI λ repressor immune complexes in the absence or presence of specific goat anti–mouse IgG2a F(ab)′2 fragments, in order to induce cell activation through endogenous surface IgG2a. Cell activation through sIgG2a did not induce presentation of the cryptic epitope by FcγRII2b-expressing cells. Error bars in b and c indicate the mean variation of T cell stimulation in two distinct experiments.