Figure 1.

Naive CBY T cells do not respond to H2-DMα^−/− APCs. Splenocytes from H2-DMα^−/− and B6 mice were used to stimulate T cells isolated from naive CBY mice that were not implanted with allografts. Mixed lymphocyte reactions were cultured for 5–6 d. Cell proliferation was determined by measuring uptake of [³H]thymidine added 12–18 h before harvest. Splenocytes from (A) B6-backcrossed H2-DMα^−/− mice and (B) mixed-background B6 × 129 H2-DMα^−/− mice are inefficient activators of allogeneic T cell proliferation. (C) The reduced proliferative response is not due to a decrease in surface MHC class II expression. As expected, both mixed-background and inbred H2-DMα^−/− mice express a level of MHC class II equivalent to that of wild-type B6 animals, as detected by three anti–MHC class II antibodies. KH74 detects MHC class II–CLIP complexes poorly, and as expected, produced a smaller signal when used to label H2-DMα^−/− cells.