Figure 1. TLR3 stimulation reduces the ability of DCs to induce T-cell proliferation.

(A) 6.5 × 10³ monocyte-derived DCs were left untreated (control) or stimulated with poly(I:C) (0.5, 5, 50 or 100 μg/mL) or LPS (1 μg/mL) for 5 hours. 1 × 10⁵ allogeneic CD4⁺ T cells were added, and T-cell proliferative responses were measured by [³H] thymidine incorporation after 72 hours. Results from seven independent experiments are expressed relative to the T-cell proliferation induced by unstimulated DCs (on average 34,326 cpm). Box plots display medians, 25th and 75th percentiles as boxes, and 10th and 90th percentiles as whiskers. Untreated DC versus poly(I:C)-treated (50 μg/mL) DC, P = 0.04. Untreated DC versus poly(I:C)-treated (100 μg/mL) DC, P = 0.007. Untreated DC versus LPS-treated (1 μg/mL) DC, P = 0.003. (B) CD4⁺ T cells were cultured with DCs pretreated with poly(I:C) or LPS as described in (A). IL-2 (20 ng/mL) was added after 48 hours, and proliferation was assessed by [³H] thymidine incorporation 24 hours later. Box plots represent results from five independent experiments. Untreated DC versus poly(I:C)-treated (50 μg/mL) DC, P = 0.04. Untreated DC versus LPS-treated (1 μg/mL) DC, P = 0.01. (C) The effect of poly(I:C) on alloantigen- or superantigen-driven T-cell responses was compared by culturing CD4⁺ T cells with DC that were untreated, loaded with TSST-1, pretreated with poly (I:C) (100μg/mL), or pretreated with poly(I:C) plus TSST-1 (100μg/mL and 0.04 ng/mL, respectively). Cultures were initiated at a DC:T-cell ratio of 1:50, and proliferative responses were quantified by ³H-thymidine incorporation after 72 hours. Assays were performed in triplicates, and results are presented as mean ± SD. Untreated DC versus poly(I:C)-treated DC, P=0.02; TSST-1-loaded DC versus TSST-1 plus poly(I:C)-treated DC, P=0.01.