IL-17 and infections.

IL-17 immunity has been shown to be essential for mucocutaneous protection against Candida albicans in mice and humans. However, mice with defective IL-17 immunity display broader susceptibility, as they are also prone to infections with diverse infectious agents at various sites. Humans with genetic defects affecting their IL-17 immunity usually suffer from chronic mucocutaneous candidiasis (CMC): recurrent or persistent infections of the skin, nails, and mucosae with C. albicans, with or without other clinical signs. Most patients with autosomal dominant (AD) hyper-IgE syndrome (HIES) due to STAT3 deficiency or AD STAT1 gain-of-function display impaired IL-17-producing T-cell development, and CMC is one of their principal clinical manifestations. Similarly, patients with autosomal recessive (AR) autoimmune polyendocrine syndrome type 1 (APS-1) caused by AIRE deficiency have high levels of neutralizing autoantibodies against IL-17A, IL-17F and/or IL-22 and present CMC as their only infectious disease. Finally, CMC is the main clinical phenotype observed in patients with inborn errors specifically affecting IL-17 immunity. Indeed, patients with AD IL-17F deficiency or AR IL-17RA or ACT1 deficiency display CMC and, to a lesser extent, superficial staphylococcal diseases. Candida infection was recently reported in psoriasis patients treated with anti-IL-17A antibodies. Careful monitoring for CMC is thus important during anti-IL-17 treatment.