P. chabaudi-infected erythrocytes inhibit the ability of DCs to efficiently activate naive T cells in vitro. DCs (2 × 105) were treated with infected (pRBC) or uninfected (RBC) erythrocytes for 24 h. DCs were then loaded with 5 mg/ml of OVA for 6 h. 5 × 105 untreated (Control), RBC or pRBC-treated DCs and 5 × 105 DO11.10 lymph node cells were then co-cultured. (a) CD69 expression assessed on DO11.10 T cells 24 h later by FACS analysis. Results are expressed as the percentage of antigen-specific cells expressing CD69 in cultures stimulated by OVA-pulsed DCs (filled bars) or by DCs only (open bars). Results show the mean of triplicate samples ± s.e. (b) [3H]thymidine was added for the last 18 h of culture; c.p.m., counts per min. Results show mean proliferation of OVA-specific T cells after incubation with DCs treated with uninfected RBCs (open circles) or pRBCs (filled circles) in triplicate samples ± s.e. The concentrations of (c) IL-2, (d) IL-5 (e) IL-10, and (f) IFN-γ secreted by OVA-specific T cells after incubation with DCs treated with uninfected RBCs (open circles) or pRBCs (filled circles) were measured in supernatants harvested after 24, 48, and 72 h of culture.