P. chabaudi-infected erythrocytes do not activate DCs directly in vitro. DCs (2 × 106) were cultured with 2 × 108 infected erythrocytes (DC+pRBC; filled circles) or with an equal number of uninfected erythrocytes (DC+RBC; empty circles). Control DCs remained unstimulated (DC; empty squares) or were stimulated with 1 μg/ml of LPS (DC+LPS; filled squares). Results show the mean fluorescence intensity of (a) MHC class II, (b) CD40, (c) CD80, and (d) CD86, as determined by FACS analysis of gated CD11c+ cells at various times of co-culture. Supernatants were analyzed for concentrations of (e) IL-12 (p40 subunit) and (f) IL-10 secreted by DCs after 24 h of incubation. (g) The number of viable DCs was determined by trypan blue exclusion. Results show the mean value ± standard error (s.e.) of triplicate samples per group.