Tlr9 expression protects against Tlr7-dependent exocrine gland and systemic disease manifestations in primary Sjögren's disease in a sex-biased manner

Abstract

Primary Sjogren's disease (pSD) is a systemic autoimmune disease. Currently, the causes of pSD remain unknown, and no curative therapies are available. Our prior studies showed Tlr7 activation was an important driver of pSD in females. Since Tlr7 is regulated by Tlr9, we hypothesized that ablation of Tlr9 would exacerbate disease in a Tlr7-dependent manner. Towards this end, we generated pSD mice that lacked systemic expression of either Tlr9 (NOD.B10^Tlr9-/-) or both Tlr7 and Tlr9 (NOD.B10^Tlr−DKO). We harvested tissues for histologic analysis and assessed disease-relevant immune cell populations in secondary lymphoid organs. We examined total and autoreactive antibody levels in sera. Enhanced nephritis was observed in Tlr9-deficient females, while dacryoadenitis was increased in males that lacked Tlr9, and these manifestations were dependent on Tlr7. Moreover, the percentages of splenic Tlr7+ B cells, germinal center and age-associated B cells, CD4⁺ and CD8⁺ activated/memory T cells, and Tfh cells were increased in NOD.B10^Tlr9-/- females as compared to sex-matched NOD.B10 mice, and this expansion was abrogated in NOD.B10^Tlr−DKO females. Finally, total IgM levels were elevated in sera from NOD.B10^Tlr9-/- females as compared to the parental strain and autoreactive IgM and IgG were also enriched in NOD.B10^Tlr9-/- females. NOD.B10^Tlr−DKO females and males showed dramatically reduced IgM and IgG titers as compared to the NOD.B10 strain and anti-nuclear autoantibodies were diminished in this strain. Overall, our study revealed that ablation of Tlr9 drives pSD in females but has negligible effects on disease in males. Moreover, Tlr9 regulates Tlr7-dependent pSD manifestations in a sex-biased manner.