Alpha-toxin elicited CX3CL1-release via ADAM10 inStaphylococcus aureuspneumonia impairs bactericidal function of human monocytes

ABSTRACT Staphylococcus aureus is an important human pathogen causing severe invasive infections. Pathogenesis is attributed to a wide array of virulence factors, including several potent exotoxins such as the pore-forming alpha-toxin. In this study, we found that patients with S. aureus respiratory tract infections had elevated CX 3 CL1 levels in airway fluid and plasma. Using humanized organotypic lung models, we observed that stimulation of lung epithelium with alpha-toxin induce an intensified CX 3 CL1 expression apically in the epithelium as well as the release of CX 3 CL1. Blocking alpha-toxin or ADAM10 activity in organotypic lung using an alpha-toxin-blocking antibody or a specific ADAM-10 inhibitor confirmed their role in modulating CX 3 CL1 cleavage and release. Analyses of CD14 + human monocytes in combination with a CX 3 CR1 inhibitor revealed that alpha-toxin-mediated CX 3 CL1 release induce CX 3 CL1-dependent chemotaxis. In line with these data, lung tissue from patients with S. aureus respiratory tract infection showed elevated CX 3 CL1 and CD14 staining as compared to tissue from patients with non-infectious lung diseases. Functional studies of monocytes showed that CX 3 CL1 released by lung models resulted in upregulated CD83 and downregulated CD86, as well as impaired killing of phagocytosed S. aureus . Furthermore, stimulation of monocytes with soluble CX 3 CL1 hampered their reactive-oxygen and nitric-oxide production. Taken together, our data show that S. aureus triggers the release of lung epithelial CX 3 CL1; a process found to be dependent on the alpha-toxin’s effect on ADAM10 mediating cytotoxicity and resulting in impaired monocyte phagocytic killing. Hence, we identify an immunomodulatory effect of alpha-toxin involving the CX 3 CL1-ADAM10 axis extending beyond the cytolysis function.