Toll-Like Receptor 4 Is Required for Optimal Development of Th2 Immune Responses: Role of Dendritic Cells

Abstract

LPS potently induces dendritic cell maturation and the production of proinflammatory cytokines, such as IL-12, by activation of Toll-like receptor 4 (TLR4). Since IL-12 is important for the generation and maintenance of Th1 responses and may also inhibit Th2 cell generation from naive CD4 T cell precursors, it has been inferred that TLR4 signaling would have similar effects via the induction of IL-12 secretion. Surprisingly, we found that TLR4-defective mice subjected to sensitization and pulmonary challenge with a protein allergen had reductions in airway inflammation with eosinophils, allergen-specific IgE levels, and Th2 cytokine production, compared with wild-type mice. These reduced responses were attributable, at least in part, to decreased dendritic cell function: Dendritic cells from TLR4-defective mice expressed lower levels of CD86, a costimulatory molecule important for Th2 responses. They also induced less Th2 cytokine production by antigenically naive CD4 T cells in vitro and mediated diminished CD4 T cell Ag-specific pulmonary inflammation in vivo. These results indicate that TLR4 is required for optimal Th2 responses to Ags from nonpathogenic sources and suggest a role for TLR4 ligands, such as LPS derived from commensal bacteria or endogenously derived ligands, in maturation of the innate immune system before pathogen exposure.

A Novel Role of Cysteinyl Leukotrienes to Promote Dendritic Cell Activation in the Antigen-Induced Immune Responses in the Lung

“…In some experiments, DCs were also obtained from mice treated with Mk (1 mg/kg) on days 0 -10 after OVA sensitization on day 0. As in a previous report (32), the positively selected cells from spleens were routinely Ͼ85% CD11c ϩ , and there was no significant difference in the purity of CD11c ϩ cells between each group of mice in every experiment. Positively selected DCs were incubated with mitomycin-C (10 g/ml; Sigma-Aldrich) for 35 min at 37°C in a humidified atmosphere containing 5% CO 2 , then washed four times with PBS.…”

“…On day 21, DCs in the lung of mice treated as described above were positively selected as previously reported (32). In brief, lung tissues were minced and then treated with 0.033% (w/v) collagenase/complete DMEM solution for 90 min.…”

“…The purity of CD4 ϩ cells, confirmed by the flow cytometry, was Ͼ95%. DCs were also selected from spleen cells of the OVA-sensitized mice, using MACS CD11c microbeads following the manufacturer's protocol as previously reported (32). Then CD4 ϩ T cells (2.5 ϫ 10 5 cells/ml) were cocultured with DCs (5 ϫ 10 4 cells/ml) under OVA stimulation (1000 g/ml) in a 96-well, flat-bottom microtiter assay plate.…”

Toll-Like Receptors in Health and Disease: Complex Questions Remain

“…Contrary to expectations, TLR4 Ϫ/Ϫ mice also showed a role for TLR4 in driving Th2 cytokine generation through modulation of DC costimulatory molecule expression (72), and LPS stimulation amplified Th2 responses in a mouse model of allergic airway inflammation (73). Some data also suggest that TLR2 activation can favor Th2 phenotypes by induction of IL-12 p40 homodimers and a reduced capacity for production of bioactive IL-12 p70 (74,75).…”

Epigenetic inheritance of fetal genes in allergic asthma

“…Asthma has been associated with an exaggerated T-helper type 2 (Th2) over Th1 responses to allergic and nonallergic stimuli (2,3), which leads to chronic airway inflammation (4,5). Alternative hypotheses may be that the innate immune system may also be specially programmed for anti-infectious defense and abnormally programmed in inflammatory disease such as asthma (6,7).…”