Figure 3.

The CD4 T cell selection pathway is responsible for IL-4–producing Th1 cells. (A) WT→B6, CIITA^Tg→B6, and CIITA^Tg→CIITA^−/− chimeric mice were generated as described in Materials and methods. 11 wk after reconstitution, splenic CD4 T cells were differentiated under Th1- or Th2-inducing conditions for 6 d. Differentiated cells were then restimulated with PMA and ionomycin and analyzed for IFN-γ and IL-4 production. (B) CIITA transgene expression in the absence of MHC class II cannot generate IL-4–producing Th1 cells. BM from WT, CIITA^Tg, or CIITA^Tg/Aβ^−/− mice were transplanted into lethally irradiated B6 mice. Differentiated Th1 or Th2 cells from the mice reconstituted for 3 mo were assayed for cytokine production by ICS. The percentage of positive cells in each quadrant is shown.