TLR2/TLR4-dependent exaggerated cytokine production in hyperimmunoglobulinaemia D and periodic fever syndrome.

OBJECTIVE: The autoinflammatory hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS) is characterized by recurrent episodes of fever and inflammation. As part of the mevalonate kinase deficiency spectrum, it is caused by MVK mutations, resulting in decreased mevalonate kinase activity in the isoprenoid pathway. Although IL-1ß is considered a major cytokine in its pathogenesis, IL-1 blockade is not successful in a proportion of patients. We aimed to further characterize the pro-inflammatory cytokine profile of HIDS. METHODS: Peripheral blood mononuclear cells from HIDS patients and healthy donors were incubated with several stimuli. Cytokine concentrations were detected by ELISA. To analyse mRNA and protein expression, we performed quantitative RT-PCR and western blot, respectively. RESULTS: We observed significant differences in cytokine production when cells were incubated with ligands for Toll-like receptor 2 (TLR2), TLR4 and nucleotide-binding oligomerization domain-containing 2 (NOD2). The increased ratio between active and inactive caspase-1 protein in HIDS patients could explain why these cells are more easily triggered to secrete IL-1ß. This is apparently not regulated at the transcriptional level, since expression levels of caspase-1 and IL-1ß mRNA were similar in patients and controls. Both anakinra and tocilizumab treatment resulted in decreased inflammation, both ex vivo as well as in vivo. CONCLUSION: The increased cytokine secretion in HIDS is specific for TLR2, TLR4 and NOD2 ligation. Although IL-1ß is important in the HIDS pathology, our data suggest it is a multicytokine disease. A more rigorous clinical trial is required to determine whether IL-6 receptor blockade may be considered in patients not responding to anakinra treatment.

Respiratory syncytial virus infection augments NOD2 signaling in an IFN-ß-dependent manner in human primary cells.

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections in infants, with remarkable variability in disease severity. An exaggerated proinflammatory response and influx of leukocytes is part of the pathogenesis of severe RSV disease. Here, we show an increase in proinflammatory cytokine production by human immune cells after stimulation with RSV and muramyl dipeptide (MDP), which is recognized by nucleotide-binding oligomerization domain containing 2 (NOD2). PBMCs from Crohn's disease patients homozygous for the 3020insC mutation in the NOD2 gene did not show a synergistic response to stimulation with RSV and MDP, suggesting that NOD2 is essential for the observed synergy. Further experiments aimed at identifying the viral ligand indicated that viral RNA plays an essential role in the recognition of RSV. Stimulation with RSV or Poly(I:C) induced IFN-ß expression, which resulted in an increased expression of the viral receptors TLR3 and RIG-I, as well as an increased NOD2 expression. Our data indicate that IFN-ß induction by viral RNA is an essential first step in the increased proinflammatory response to MDP. We hypothesize that the enhanced proinflammatory response to MDP following RSV infection may be an important factor in determining the outcome of the severity of disease.

TLR2 promotes Th2/Th17 responses via TLR4 and TLR7/8 by abrogating the type I IFN amplification loop.

TLR2 plays an important role in the removal of Gram-positive bacteria; contrastingly, it also appears to have important protective effects against unrestrained inflammation and subsequent organ injury during infection and autoimmunity. We hypothesized that TLR2 tunes the phenotype of dendritic cells (DCs) activated through other TLRs, thereby fulfilling a crucial role in the modulation of the immune response. TLR2 potently inhibited TLR4- and TLR7/8-induced cytokine production by human DCs. The inhibitory effect of TLR2 on the release of TNF-alpha but not of IL-12p70 was mediated by PI3K. TLR2 inhibits the production of IL-12p70 by dampening the type 1 IFN amplification loop. When DCs were triggered with the potent synergistic combination of LPS (TLR4) and R848 (TLR7/8) in conjunction with a TLR2 ligand, a clear shift to more Th2- and Th17-prone responses in the naive and memory T cell subpopulations was observed. This shift in T cell responses was inherent to the inability of TLR2-stimulated DCs to produce IL-12p70 and was dependent on the production of IL-1 and IL-6.