Fig. 1.

Siglec-15-Fc binds lung and breast adenocarcinoma cell lines. For the binding assay, recombinant Siglec-15 human IgG1 Fc fusion protein (Siglec-15-Fc) wildtype (1 μg/mL) or R143A mutant (1 μg/mL) was mixed with goat anti-human IgG Fc-FITC (1 μg/mL) to prepare immune-complexes. Lung and breast carcinoma cell lines, pretreated with or without sialidase, were incubated with Siglec-15-Fc immune complexes. Negative controls were incubations with anti-human IgG Fc-FITC without the addition of Siglec-15-Fc. The binding of Siglec-15-Fc to cancer cells was analyzed by flow cytometry. The results are mean ± SEM of fluorescence intensities (MFI) measured from three independent experiments for each lung (A) and breast (B) cancer cell line, relative to the nonstained control. ^*, P < 0.05; ^**, P < 0.01; ^***, P < 0.005; ns, not significant.