Homozygosity for rare or common hypomorphicvariants confers a predisposition to tuberculosis in humans.

UNLABELLED: Homozygosity for rare loss-of-functionvariants abolishes IL-23-dependent IFN-γ production by lymphocytes, including NK and innate-like T cells, thereby underlying clinical disease due to weakly virulent mycobacterial species. We report selective enrichment in homozygosity for four hypomorphicvariants in our cohort of patients with tuberculosis. Three of thesealleles are rare (G300V, G149R and L372F), with a minor allele frequency (MAF) under 1%, but the fourth (R381Q) is surprisingly common, with a MAF as high as 10.2% in certain populations. The other 15 missense alleles found in the homozygous state in public databases are isomorphic. The four hypomorphic IL-23R variants identified dimerize with IL-12Rβ1 and bind IL-23. However, their function is impaired by low levels of cell-surface expression (R381Q, G300V) and/or as a consequence of conformational changes altering agonist efficacy. IFN-γ production in response to IL-23 is impaired in innate-like T cells and NK cells. These data suggest that recessive partial IL-23R deficiency, whether due to rare or common variants, confers a predisposition to tuberculosis while preserving immunity to less virulent mycobacteria.

ONE SENTENCE SUMMARY: Homozygous hypomorphicvariants impair IL-23-dependent IFN-γ production and underlie tuberculosis.