Introduction: Toll-like Receptor-10 (TLR10) remains the only TLR family member without a known ligand and clearly-defined functions. As the most potent producers of type-I and type-III interferons, plasmacytoid dendritic cells (pDCs) play a key role in innate sensing and mounting of the immune response to viruses. Unlike other TLRs, the role of TLR10 in pDCs has not been characterized. Here, we have interrogated if human pDCs express TLR10. We have further investigated how the functionality of pDCs is affected upon antibody-mediated engagement of TLR10.
Methods: PBMCs were isolated from heparinized blood from healthy volunteers via ficoll-hypaque gradient centrifugation. The expression of TLR10 was measured in pDCs compared to other immune cells via flow cytometry. The expression of TLR10 was compared between two known subsets of human pDCs: CD2high and CD2low. PBMCs were pre-incubated with anti-TLR10 antibody and stimulated with different viruses. The effect of TLR10 engagement was measured by comparing cytokine production and expression of co-stimulatory markers by pDCs upon pre-incubation with an anti-TLR10 antibody or matching isotype.
Results: Human pDCs constitutively express TLR10 which is comparable in both CD2high and CD2low pDCs. Treatment with different viral stimuli and cytokine failed to alter TLR10 expression on pDCs. Upon pre-incubation with an anti-TLR10 antibody, production of IFN-α, TNF-α, IL-6, and IFN-λ was downregulated in response to stimulation with DNA and RNA viruses. Similar effects were seen on monocytes. pDCs, purified from healthy donors via magnetic bead-based negative selection, also produced a significantly lower level of type-I interferon in response to viral stimuli upon prior antibody-mediated TLR10 engagement.
Conclusions: Our data provide the first evidence that TLR10 is constitutively expressed on the surface of human pDCs and works as a regulator of their innate response.