〔Abstract〕 Objective To investigate the role of caspase recruitment domain-containing protein 9(Card9) inAspergillus fumigatus(A.fumigatus) keratitis and the effect of its deficiency on macrophage resistance to fungal infection. Methods (1) C57BL/7 mice aged 6-8 weeks were selected and the mice pretreated Card9 siRNA and Blank siRNA, respectively, and the expression of Card9 in each group was detected by Western blot and RT-PCR. The corneal epithelium of the mice was scraped away 72 hours later, andA.fumigatusspore suspension was injected into the corneal stroma. The corneal scores were recorded at 1 d, 3 d, 5 d and 7 d after infection. The expression of Card9, nuclear factor κB(NF-κB), interleukin 1β(IL-1β), interleukin 6(IL-6) and tumor necrosis factor α(TNF-α) in each group was detected by RT-PCR and immunohistochemical(IHC).(2) Human corneal epithelial cells(HCECs) and human monocytic-leukemia cells(THP-1)in vitro, RT-PCR was used to examine the expression of Card9 gene in the two cells, and a stable cell line of THP-1 cells was constructed using shRNA vectors. The expression of Card9 in the cell line was detected by Western Blot and RT-PCR. The cells were induced into macrophages and stimulation byA.fumigatus, and the expression of Card9, NF-κB, IL-1β, IL-6 and TNF-α was detected by RT-PCR. Results Card9 expression increased inA.fumigatuskeratitis, mainly distributed in cytoplasm of immune cells. The expression of Card9 in the cornea of mice treated with Card9 siRNA was significantly reduced. After inhibiting the expression of Card9 gene, the expressions of Card9, NF-κB, IL-1β, IL-6 and TNF-α significantly decreased and the changes of IL-1β were most significant. Inin vitrostudies, Card9 exhibited negligible expression in human corneal epithelial cells, contrasting with its pronounced expression in THP-1 cells. After the induction of macrophages, Card9, NF-κB, IL-1β, IL-6, and TNF-α were significantly upregulated under the stimulation ofA.fumigatus. After inhibiting the expression of Card9, the stimulated expression of these factors was significantly reduced, with the most notable change observed in IL-1β. Conclusion Card9 is involved in the inflammatory development and healing process ofA.fumigatuskeratitis. Card9 deficiency can cause functional impairment of macrophages and inhibit the expression of inflammatory factors to a certain extent, in which IL-1β has the greatest effect.