TLR4 is essential for the induction of IL-23 expression in mouse skin by tape stripping and for the IL-22 response to EC immunization. (A–D) Il23p19 mRNA expression 6 h after tape stripping of the ear skin of WT mice housed under GF versus specific pathogen–free (SPF) conditions (A); Myd88^−/− and Trif^−/− mice and WT controls (B); Il1r1^−/−, Il18r^−/−, Il1rl1^−/−, and Il1r1^−/− mice treated with anti-ST2 and anti–IL-18–neutralizing mAbs or control IgG (C); Tlr2^−/−, Tlr5^−/−, Unc93b^−/−, and TLR4 mutant (mut.), C3HeJ mice, and WT controls (D). (E) S100a8 and S100a9 mRNA expression 6 h after tape stripping of ear skin. (F) Il23p19 mRNA expression 3 h after i.d. injection of low MW HA or rS100a8 in the back skin of TLR4 mutant mice and WT controls. (G) Il23p19 mRNA expression in Pam212 cells stimulated for 6 h with low MW HA with or without preincubation with the indicated inhibitors of NFKβ (BAY-11-7082), p38 (SB 203580), ERK (U-0126), or JNK (SP600125). Results in A–F are derived from at least five mice for each group. Results in G represent four independent experiments. Columns and bars in A–F and horizontal and vertical bars in G represent mean and SEM. *, P < 0.05; **, P < 0.01; ns, not significant, two-tailed Student’s t test.