All eight TYK2-deficient patients displayed impaired but not abolished cellular responses to (a) IL-12 and IFN-α/β, accounting for mycobacterial and viral infections, respectively; (b) IL-23, with normal proportions of circulating IL-17(+) T cells, accounting for their apparent lack of mucocutaneous candidiasis; and (c) IL-10, with no overt clinical consequences, including a lack of inflammatory bowel disease.
Recent studies on patients with recurrent mucocutaneous candidiasis have led to the discovery of mutations in CARD9 and DECTIN-1, genes key to the production of the Th17-driving cytokines IL-1beta, IL-6, and IL-23.