FIG. 6.

The use of 2fTGH and G3A cells to delineate the physiologic importance of CIITA in IFN-γ-mediated gene suppression. (A) The experiment was performed as described in the legend Fig. 3, except 2fTGH cells were treated with 500 U of IFN-γ/ml (lanes 1 and 2) 24 h after transfection. The inhibition of col-CAT activity by IFN-γ treatment in these cells is shown. This suppression is observed with CIITA or CIITA(1-94) but not with CIITA(1-58). (B) G3A cells were used in place of 2fTGH cells, and the experiment was performed as for panel A. col-CAT activity was not inhibited by IFN-γ treatment in G3A cells (lanes 1 and 2). The inclusion of exogenously expressed CIITA inhibited col-CAT activity (lanes 3 and 4). (C) The DRA-Luc control shows that the addition of IFN-γ to the same culture of G3A cells did not result in MHC-II promoter activation (compare lanes 1 and 2). In contrast, the addition of CIITA resulted in the induction of the MHC-II promoter. These experiments were reproduced three times. Luc, luciferase; wt, wild type.