Natural Loss-of-Function Mutations in Qa2 and NCF1 Cause the Spread of Mannan-Induced Psoriasis.

A basis for the genetic predisposition to psoriasis is a single locus, PSORS1, within the major histocompatibility complex I region. This murine major histocompatibility complex locus encodes nonclassical molecules such as Qa2. We hypothesized that a natural loss-of-function variant of Qa2 gene clusters promotes psoriasis. In this study, we have developed a mannan-induced psoriasis model with the double deficiency of Qa2 and ROS owing to natural mutations of Qa2 gene clusters and the Ncf1 gene in the C57BL/6 background, respectively. We report three key findings in mice with mannan-induced psoriasis. A complete deficiency of Qa2 resulted in the expansion of IL-17‒producing γδ T cells and group 3 innate lymphoid cells in draining lymph nodes, leading to ear psoriasis. A single copy of Qa2-encoding genes was enough to protect against mannan-induced psoriasis, and such a protection was erased by a mutated Ncf1. Double defects with Qa2 and Ncf1 elicited a spread of exaggerated ear psoriasis to the nails, and the deficiency of γδ T cells reduced the severity of nail psoriasis. Collectively, these findings in mice provide evidence for the importance of Ncf1 mutations and Qa2 gene clusters, possibly corresponding to the PSORS1 locus in the spread of psoriasis.