Investigating the potential impact of gut microbiota and immune cells on ankylosing spondylitis based on single-cell sequencing and genetic variation analysis.

OBJECTIVES

Several observational studies suggest that gut microbiota (GM) may influence the onset and progression of ankylosing spondylitis (AS) through modulating host immune responses. However, the potential genetic associations between GM and AS susceptibility, as well as the immune-mediated mechanisms, remain to be elucidated.

METHOD

This study initially infers the causal associations among GM, immune cell traits (ICTs), and AS using univariate two-sample Mendelian randomization (MR), and then evaluates the mediating role of ICTs in the genetic association between GM and AS through mediation MR analysis. Meanwhile, single-cell RNA sequencing is conducted on vertebral bone marrow blood samples obtained from three AS patients and three controls to characterize the differentiation status and functional alterations of relevant immune cell subsets, thereby validating their contribution to the pathogenesis of AS.

RESULT

Mediation MR analysis revealed that "HLA-DR on CD14- CD16 + monocytes" acts as a protective factor for AS, attenuating the causal effect of Genus Sutterella/Sutterella Wadsworthensis on disease susceptibility. Single-cell analysis revealed distinct differences in cellular composition and transcriptional profiles between AS and the controls. Notably, monocyte subset analysis indicated a significant reduction in CD14- CD16 + monocytes in AS, concomitant with the relatively high expression of cellular activation markers.

CONCLUSION

The study indicates that CD14- CD16 + monocytes are potential protective factors for AS and exert a negative mediating effect on the causal associations between GM and AS. Boosting non-classical monocytes or modulating Sutterella abundance could help prevent or treat AS. Key Points • Novel approach integrating mediation MR and scRNA-seq offers distinct analytical strengths. • New insights into the gut-immune axis reveal its role in immune dysregulation in AS. • Mediation MR and single-cell analysis reveals CD14- CD16 + monocytes as protective factors in AS. • HLA-DR on CD14- CD16 + monocytes mitigate the genetic effect of Sutterella on AS susceptibility.