The Role of Toll-like Receptors (TLRs) in Bacteria-induced Maturation of Murine Dendritic Cells (DCs): PEPTIDOGLYCAN AND LIPOTEICHOIC ACID ARE INDUCERS OF DC MATURATION AND REQUIRE TLR2

Kathrin S Michelsen,Alexandra Aicher,Mariette Mohaupt,Thomas Hartung,Stefanie Dimmeler,Carsten J Kirschning,Ralf R Schumann

doi:10.1074/jbc.m011615200

Abstract

Toll-like receptors (TLRs) have been found to be key elements in pathogen recognition by the host immune system. Dendritic cells (DCs) are crucial for both innate immune responses and initiation of acquired immunity. Here we focus on the potential involvement of TLR ligand interaction in DC maturation. TLR2 knockout mice and mice carrying a TLR4 mutation (C3H/HeJ) were investigated for DC maturation induced by peptidoglycan (PGN), lipopolysaccharide (LPS), or lipoteichoic acids (LTAs). All stimuli induced maturation of murine bone marrow-derived DCs in control mice. TLR2(-)/- mice lacked maturation upon stimulation with PGN, as assessed by expression of major histocompatibility complex class II, CD86, cytokine, and chemokine production, fluorescein isothiocyanate-dextran uptake, and mixed lymphocyte reactions, while being completely responsive to LPS. A similar lack of maturation was observed in C3H/HeJ mice upon stimulation with LPS. DC maturation induced by LTAs from two different types of bacteria was severely impaired in TLR2(-)/-, whereas C3H/HeJ mice responded to LTAs in a manner similar to wild-type mice. We demonstrate that DC maturation is induced by stimuli from Gram-positive microorganisms, such as PGN and LTA, with similar efficiency as by LPS. Finally, we provide evidence that TLR2 and TLR4 interaction with the appropriate ligand is essential for bacteria-induced maturation of DCs.

Highlights

Toll-like receptors (TLRs) have been found to be key elements in pathogen recognition by the host immune system
Dendritic cells (DCs) maturation induced by lipoteichoic acids (LTAs) from two different types of bacteria was severely impaired in TLR2؊/؊, whereas C3H/HeJ mice responded to LTAs in a manner similar to wild-type mice
Expression of Costimulatory Molecules and MHC Class II Molecules Is Impaired in TLR2-deficient Mice upon Stimulation with PGN—To assess whether PGN-induced maturation of DCs is initiated via TLR2, we examined the responsiveness of DCs from TLR2-deficient mice to PGN and, as control, to LPS

Summary

MHC II

Bone marrow-derived immature DCs from TLR2Ϫ/Ϫ and wild-type littermates were cultured with the indicated concentrations of PGN for 4 (TNF-␣) and 24 h (all others), respectively. Concentrations of IL-6 (A), TNF-␣ (B), IL-12p40 (C), and MIP-2 (D) in the culture supernatant were measured by ELISA. Mean values Ϯ S.D. of four independent experiments (A, C, and D) or of two experiments (B) are shown. P Ͻ 0.05 is indicated by asterisks. Indicate that interaction with the corresponding ligands of TLRs during bacteria-induced maturation is required for both the up-regulation of cell surface MHC class II and costimulatory molecules on mature DCs. Cytokine secretion of DCs depends on TLR integrity, because it is severely impaired in TLR2-deficient mice upon stimulation with PGN and highly purified LTA and in C3H/HeJ mice upon stimulation with LPS and lipid A

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION