Background Toll-like receptor (TLR) agonists are widely used as adjuvants in specific immune therapy protocols for patients with atopic disposition. Monocyte-derived dendritic cells (mDCs) are thought to be important target cells for these compounds.
Objectives To compare surface markers, TLR expression, TLR functionality after ligand stimulation, and genetic polymorphisms in the TLR 2-, 3-, and 4-genes in mDCs from atopic vs. non-atopic patients.
Methods mDCs from highly atopic individuals (total serum IgE >1000 IU/mL) and healthy control persons (total serum IgE <75 IU/mL) were screened for TLR 1-10 expression by real-time PCR. Receptor function was analysed by IL-12 and TNF-α production after incubation with the respective ligands peptidoglycan (PGN) (TLR 2), polyriboinosinic-polyribocytidylic acid (poly IC) (TLR 3), lipopolysaccharide (LPS) (TLR 4), flagellin (TLR 5), and CpG-DNA/non-CpG-DNA (TLR 9). Haplotype-tagging single-nucleotide polymorphisms of the TLR 2-, 3-, and 4- genes were analysed for genetic associations.
Results mDC from atopic patients showed a very similar pattern of TLR expression as controls with strong expression of TLR 2, 4, 5, 6, and 8, moderate expression of TLR 1 and 3, and no or very low expression of TLR 7, 9, and 10. After stimulation with TLR ligands, mDCs from atopic patients acquired a mature phenotype with a tendency towards a higher up-regulation of the co-stimulatory molecules CD80, CD83, and CD86 than control mDCs. IL-12 and TNF-α were produced at a similar level in both groups of DCs. Among the different TLR agonists, poly IC showed the strongest activation of DCs, followed by LPS, PGN, and flagellin. This was paralleled by a strong functional expression of protein kinase R and retinoid-inducible gene-I (RIG-I), two additional poly IC-sensing receptors in both groups. Genetic analysis of single-nucleotide polymorphisms in the TLR 2-, 3-, and 4-genes in both groups revealed no major allele or genotype differences.
Conclusions mDC from atopic patients are not restricted in their response to TLR-ligands. TLR agonists seem to be suitable to induce pro-inflammatory immune responses and maturation in mDCs from highly atopic individuals and represent reasonable adjuvants for specific immunotherapy reagents.