Objectives: CXCL16 is a member of CXC chemokine, which is synthesised in plasmacytoid dendritic cell as a transmembrane molecule. Transmembrane CXCL16 on plasmacytoid dendritic cell plays a role in binding, uptaking and accumulation of CpG D ODN in early endosomes rather then lysosomal vesicles, thereby causing a high level of interferon-alpha secretion. Previously, we disclosed pronounced interferon-alpha production from these cells in patients with Behçet's disease. The aim of this study was to investigate the relation between the secretion of IFN-α and the expression of CXCL16 on surface of plasmacytoid dendritic cell from patients with Behçet's disease, and compare it with patients with ankylosing spondylitis and healthy controls.
Methods: The study population consisted of 73 cases (35 with Behçet's disease, 19 with ankylosing spondylitis and 19 controls). We investigated the expression of CXCL16 on surface of plasmacytoid dendritic cells by flow cytometry, and the serum levels of IFN-α and CXCL16 with ELISA.
Results: Serum levels of IFN-α in patients with Behçet's disease were significantly higher than the controls (p=0.009), and than patients with ankylosing spondylitis, but not statistically significant (p=0.124). Serum levels of CXCL16 in patients with Behçet's disease and patients with ankylosing spondylitis were significantly higher than controls (p=0.009, p=0.003, respectively). We found no difference in the percentage and MFI of plasmacytoid dendritic cells and CD123+CXCL16+ cells determined by flow cytometry among the study and control groups. In patients with Behçet's disease, a positive correlation was found between the percentage of plasmacytoid dendritic cells and CD123+CXCL16+ cells (p<0.001). Furthermore, there was also a positive correlation between the percentage of plasmacytoid dendritic cells and serum levels of CXCL16 in patients with ankylosing spondylitis (p=0.001). In addition, there was a positive correlation between the percentage of CD123+CXCL16+ cells and serum levels of IFN-α in Behçet's disease group (p=0.034). We could not find any significant difference in other comparisons.
Conclusions: We suggested that the expression of transmembrane CXCL16 on surface of plasmacytoid dendritic cell might contribute to high serum IFN-α levels seen in patients with BD.