Recently we have developed a novel method to induce IL-17 production and generate Th17 cells using exclusively microbial stimulation [18], a method that

mimics much more closely the in vivo conditions during infection. Although we can confirm defective Th17 generation and IL-17 production by cells isolated check details from patients with HIES [9–11], several important aspects are now apparent when using this improved methodology. First, defective IL-17 induction differs between stimulation with S. aureus or C. albicans. When Th17 responses were assessed both these microorganisms, which are the most important in HIES patients, were equally defective in generating CD4+ IL-17+ cells. Surprisingly, however, C. albicans

was still capable of stimulating approximately 20–30% of normal IL-17 production, while S. aureus was completely defective as an IL-17 stimulus in HIES patients (Fig. 1c). This finding is important as it may explain why it is mainly mucosal; nailbed infection is the most common Candida complication in HIES patients (83% in one large study), while systemic candidiasis is relatively rare [3]. Notably, patients with chronic mucocutaneous candidiasis who have the same clinical spectrum of Candida infection [19] have also been reported to have a specific defect in Candida-induced GSK2126458 IL-17 production [20]. This supports the conclusion that IL-17 is important in mucosal anti-Candida host defence and that the lower IL-17 found in our patients is indeed clinically relevant. Secondly, an important observation of our study is represented by

stiripentol indistinguishable immunological responses in patients with the ‘classical’ clinical form of HIES, independent of the presence or absence of STAT3 mutations. All the patients who had a strong phenotype of the disease displayed similar defects in IL-17 production and Th17 generation. Our data are supported by the report of one HIES patient without STAT3 mutation and defective Th17 responses [21], and suggests strongly that in patients with the ‘classical’ presentation of HIES, but in which no STAT3 mutation is found, defects in the same immunological pathways are the most probable cause of the disease. This may also imply that defective Th17 responses are a more sensitive diagnostic tool for HIES. Thirdly, one of the most interesting findings of our study is the description of a clear association of a milder phenotype of the disease in a Dutch family with a less severe defect in IL-17 production, due probably to the linker domain triplet that did not lead to a frameshift [13]. Patients from this family suffer from skin infections with S. aureus, candidiasis of the nailbeds (but not of the mucosae), dermatitis, hyper-IgE and eosinophilia, but they lack any respiratory infections (either with S. aureus or other pathogens).