Constitutive presentation of self antigens by immature splenic DCs. (A) Splenic DCs were purified from untreated or CpG-injected OVA⁺ transgenic mice, which express a membrane-bound form of OVA,²²  and then fixed. The indicated number of fixed DCs were incubated with the anti-OVA hybridoma Ob4 (left graph) or with naive OVA-specific OT-II cells (right graph). IL-2 secretion and OT-II proliferation were determined by ELISA 1 day later or by FACS analysis 2.5 days later, respectively. AU indicates arbitrary units. Data for experiments were obtained in duplicate; bars represent the range of the values obtained. (B) MHC II molecules were immunoprecipitated from total splenocytes, a fresh preparation of splenic DCs, and CD4⁺, CD8⁺, and CD4^–CD8^– DCs purified by preparative FACS from the total splenic DC preparation. Immunoprecipitates were loaded in a 12.5% SDS-PAGE without (nb) or after boiling (b) and analyzed by Western blot with a rabbit serum specific for the I-A α-chain. The positions occupied in the blot by the αβ-peptide complexes (αβ-pep) and the free I-A^b α-chain are indicated on the left.