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

Abstract

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-1β 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-1β. This is apparently not regulated at the transcriptional level, since expression levels of caspase-1 and IL-1β 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-1β 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.

Keywords: anakinra; autoinflammatory syndrome; hyper-IgD syndrome; mevalonate kinase deficiency; periodic fever; tocilizumab.