Inhibition of Toll-like receptor-9 pathway in human B cells and plasmacytoid dendritic cells by RO9021. (A), (B) Human B cells were stimulated with CpG-B (ODN2006) and IFNα for 2 days. Production of IL-6 (A) and B-cell proliferation (B) was blocked by RO9021. The proliferation was presented by total alive cells, which were quantitated by Celltiter Glow as relative luminescent units. (C) RO9021 inhibited human plasmablast differentiation. Human B cells were differentiated with ODN2006 and IL-2 for 6 days. The plasmablasts were identified as CD19+CD38+CD20– cells and presented as the percentage in total CD19+ B cells. The levels of IgM, IgG and IL-6 in the supernatants were also blocked by RO9021. (D), (E) RO9021 blocked Toll-like receptor 9 (TLR9)-mediated cytokine production in human plasmacytoid dendritic cells (pDCs). Purified pDC cells were stimulated with CpG-A (ODN2216) for 2 days. The production of IFNα (D) and TNFα (E) in supernatant were determined. Data were in duplicate and are shown as mean ± standard deviation. Statistical analysis of each treatment compared with the positive group was performed by Student’s t test. *P <0.05; **P <0.01; ***P <0.001; ns, not statistically significant. Plots shown are representative of four independent experiments tested in different donors. IC50, half-maximal inhibitory concentration.