Background: Impaired host defense mechanisms may crucially modulate the pathogenesis of atopic dermatitis (AD). More than 10% of patients with AD are heterozygous for the Toll-like receptor 2 (TLR-2) R753Q single nucleotide polymorphism (SNP) and exhibit severe eczema.
Objective: To elucidate the functional effect of the TLR-2 mutation and its putative relevance for AD.
Methods: Using the human embryonic kidney 293 transfection system, we characterized the properties of the TLR-2 R753Q SNP. Moreover, TLR-2 expression, IL-8 production, and cytokine secretion were analyzed in monocytes and CD4+ T cells of patients with AD with and without the mutant TLR-2 gene.
Results: Human embryonic kidney 293 transfectants mimicking this heterozygous mutation produced less IL-8 when stimulated with lipoteichoic acid (LTA), heat-inactivated Staphylococcus aureus or triacylated lipopeptides requiring the TLR-2/1 heterodimer. Suppressed production of IL-8 was confirmed in monocytes from patients with mutant AD after stimulation with peptidoglycan. Cell surface TLR-2 expression was severely impaired in CD3/CD28 activated CD4+ T cells of patients with AD bearing the mutant receptor, which could be restored on LTA stimulation. In contrast, LTA decreased TLR-2 expression among nonatopic individuals and patients with AD with the TLR-2 wild-type gene. T cells from patients with AD exhibited markedly suppressed IL-2 production after macrophage-activating lipopeptide-2 activation. However, no difference was found between mutant and wild-type patients with AD for IL-5, TNF-alpha, IFN-gamma, and IL-2 production.
Conclusion: Collectively, the outcome of innate and adaptive immune responses in AD is modulated by the TLR-2 R753Q SNP.