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Objective Gut‐derived innate lymphoid cell 3 (ILC3) has been shown to participate in the pathogenesis of ankylosing spondylitis (AS). CX3CR1+ mononuclear phagocytes (MNPs) have been demonstrated to modulate ILC3 function in the gut. This study was undertaken to investigate the role of proinflammatory CX3CR1+CD59+ MNPs in modulating ILC3 function in AS patients. Methods MNP subsets in the blood of AS patients and controls were analyzed by flow cytometry. The presence of CX3CR1+CD59+ cells in tissue was confirmed by confocal microscopy. Expression of the proinflammatory chemokines CX3CL1 and CCL2 and decoy receptor 6 (DcR‐6) was analyzed. Peripheral CX3CR1+CD59+ cells were cocultured with ILC3, and changes in their frequency were evaluated by flow cytometry. Transcriptome analysis of circulating CX3CR1+ monocytes was also performed. Results DcR‐6 deficiency and CCL2 overexpression were observed in inflamed tissues from AS patients. In the gut, the proinflammatory CX3CR1+CD59+ MNP population was expanded, correlated with the presence of bacteria, and produced high levels of tumor necrosis factor–like molecule 1A (TL1A) and interleukin‐23 (IL‐23). MNPs positive for CD11b, CD11c, and major histocompatibility complex class II, predominantly expressing CX3CR1, were also expanded in the small intestines of treatment‐naive SKG relative to BALB/c mice. The frequency of gut‐derived CX3CR1+CD59+CCR9+TL1A+IL‐23+ MNPs was significantly higher in the peripheral blood and synovial fluid of AS patients than controls. CCR9+CX3CR1+CD59+ monocytes were also expanded in AS synovial and bone marrow samples. Transcriptome analysis of isolated CX3CR1+CD59+ monocytes demonstrated a specific proinflammatory profile in AS. Isolated proinflammatory CX3CR1+CD59+ MNPs from AS patients induced the expansion and activation of ILC3. Conclusion Proinflammatory CX3CR1+CD59+TL1A+IL‐23+ MNPs are expanded in AS patients and display a specific proinflammatory transcriptome profile. Given the ability of these cells to support ILC3 expansion, they may promote a sustained proinflammatory status in AS.