Fig. 3

An anti-human Siglec-1 blocking antibody reduced engulfment of NTHi by human alveolar macrophages ex vivo. a Alveolar macrophages isolated from resected lung tissues of control never smokers were incubated with heat-killed and pHrode dye-labeled NTHi in the presence of an anti-human Siglec-1 blocking antibody or an isotype-matched control antibody. The bacterial engulfment was evaluated by flowcytometry. A representative histogram of pHrode-dye fluorescence was shown. A grey line indicated cells without pHrode-labeled NTHi as a negative control. A blue line showed cells treated with pHrode-labeled NTHi in the presence of an isotype-matched control antibody. A red line represented cells treated with pHrode-labeled NTHi in the presence of an anti-human Siglec-1 blocking antibody. b Bacterial engulfment was quantified by the percentage of NTHi-phagocytosed alveolar macrophages (upper panel) or by the mean fluorescence intensity (MFI) of pHrode-fluorescence in alveolar macrophages (lower panel). Anti-Siglec-1 antibody treatment reduced the engulfment ability (N = 5, *P < 0.05, Paired t-test)