Fig 1: M. catarrhalis limits ROS production in a contact-dependent and phagocytosis-independent manner by possibly binding immunosuppressive receptors(A) dHL-60 were infected or not by M. catarrhalis BBH18 strain (MOI 50) and the resulting supernatants were presented to naive ROS-induced cells.(B) ROS-induced dHL60 cells were pre-incubated with cytochalasin D (phagocytosis inhibitor) and infected with M. catarrhalis BBH18 at MOI 50. (A and B) MFI at 633 nm from at least three independent experiments at the indicated time point after infection was determined by flow cytometry. Bars represent means ± SE. MFI, Mean fluorescence intensity.(C) M. catarrhalis was incubated or not (control) with 2 µg of each human recombinant protein: CEACAM-1, Siglec-5 and Siglec-9. Antibodies raised against the recombinant proteins were used for detection by flow cytometry. MFI at 535 nm from at least three independent experiments. Bars represent means ± SE. MFI, Mean fluorescence intensity. *p < 0.05.(D) M. catarrhalis was pre-incubated or not (control) with 200 nM of each human recombinant protein: CEACAM1, Siglec-5 and Siglec-9. dHL60 cells were stimulated for ROS production and infected with Mcat (control), Mcat_CEACAM1, Mcat_Siglec-5 or Mcat_Siglec-9 at MOI of 50. MFI at 633 nm from at least three independent experiments at 2 h post-infection was determined by flow cytometry. Bars represent means ± SE. MFI, Mean fluorescence intensity. **p < 0.01; ***p < 0.001.