The aim of this study is to explore the effect of the Toll-like receptor 9 (TLR9) expressed in plasmacytoid dendritic cells (pDCs) that respond to antigen to Th2 immune deviation in allergic patients.

Subjects consisted of 19 allergic patients and 17 healthy volunteers. Skin prick tests and nasal provocation tests were performed for the two groups. Peripheral blood mononuclear cells (PBMCs) were collected from subjects and analyzed for the Lineage Cocktail (CD3, CD14, CD16, CD19, CD20, CD56) (-), HLA-DR (+), and CD123 (+) using flow cytometry. In addition, we analyzed TLR9 mRNA by reverse transcriptase-polymerase chain reaction. The level of interferon-α (IFN-α) of the PBMCs following stimulation with the TLR9 ligand CpG-ODN 2216 was also evaluated.

Analyses of CD123 (+) revealed a nearly similar distribution for the classical pDC markers in the allergic group (0.1%±0.04%) and in the controls (0.25%±0.23%). The mRNA levels of TLR9 on PBMCs were not different between the allergic group and the controls (1.29±0.41 vs. 1.25±0.23, respectively). Additionally, the level of IFN-α in PBMCs exposed to stimuli of the TLR9 ligand CpG-ODN 2216 was not significantly different between the two groups (911±829 vs. 1,095±888 pg/mL, respectively).

We found no evidence that TLR9-dependent immune responses in human pDCs are associated with allergic status.