Resses TLR4 signaling. The results presented here confirm recent studies by Gracillin biological activity Kizaki et al. [27,28] and by Wang et al. [29] that this effect is mediated by ADRB2.Other than the effects on TLR4 signaling, the interplay of adrenoceptors with TLRs involved in antiviral and antitumor immune responses has not been studied extensively. ColladoHidalgo et al. published that norepinephrine suppresses type I interferon expression via PKA (protein kinase A) [30]. While their study added substantial data about catecholamine-mediated immuno-suppression, it lacked the identification of the adrenoceptor subtype involved in suppression of TLR9 signaling. We were able to identify ADRB2 as being the relevant adrenoceptor. However, we provide convincing evidence that ADRB2 is not expressed on pDCs. In agreement with this finding, we could only observe catecholamine-dependent pDC suppression when PBMCs other than pDCs were present. We would like to point out that Collado-Hidalgo enriched pDCs to about 40 and therefore always co-cultured them in the presence of contaminating PBMCs. While we believe their conclusion that norepinephrine exerts a direct effect on pDCs has to be questioned, their original data is actually in agreement with ours. Based on our own data, we propose two possible mechanisms for catecholamine-mediated pDC suppression within PBMCs: First, upon ADRB2 stimulation, PBMC subsets might release a humoral factor directly suppressing pDCs. This was shown to be the case for suppression of TLR9 signaling in pDCs by monocytes in the presence of bacterial cell wall products [3]. Furthermore, a whole set of surface receptors inhibiting IFNA1 release (e.g., Siglec-H, NKp44, BDCA2 and more) was recently identified on pDCs [1]. It is not known, whether these surface molecules have natural ligands they interact with. Second, IFNA1 release from pDCs is enhanced by PBMCs, presumably by cytokine signaling. This is in accordance with findings of other authors [31]. ADRB2 signaling could suppress these paracrine effects. Liu and colleagues demonstrated that activated pDCs are potential inducers of antitumor responses mediated by NK cells and T cells [7]. We used an in vitro assay to investigate possible effects of epinephrine on the modulation of NK cell- dependent tumor cell lysis by pDCs. While the addition of CpG ODN-treated cell culture ASP-015K supernatants enhanced tumor cell lysis, this effect was attenuated when the supernatant was taken from cells being coincubated with epinephrine and TLR9 ligands. Since direct effects of adrenoceptor stimulation on NK cell activity have been described [32], we added propranolol with cell culture supernatants in all cases to diminish direct effects of epinephrine on NK cells. Another key function of pDCs is the initiation of appropriate antiviral immune responses [1,4]. Collado-Hidalgo demonstrated that norepinephrine facilitates replication of HIV by suppression of type I interferon responses [30]. It is conceivable that similar effects will be observed in future studies of type I interferons, pDCs and their interplay with catecholamines. It is widely accepted knowledge that the neuroendocrine system modulates immune responses via its signaling molecules acetylcholine and (nor-) epinephrine. Pharmacological modifiers of these pathways are widely used in the clinical setting, especially duringBeta2-Adrenoceptors Suppress TLR9-Dependent IFNAFigure 5. Effect of ADRB2-mediated suppression of IFNA1 release on NK cell activity.Resses TLR4 signaling. The results presented here confirm recent studies by Kizaki et al. [27,28] and by Wang et al. [29] that this effect is mediated by ADRB2.Other than the effects on TLR4 signaling, the interplay of adrenoceptors with TLRs involved in antiviral and antitumor immune responses has not been studied extensively. ColladoHidalgo et al. published that norepinephrine suppresses type I interferon expression via PKA (protein kinase A) [30]. While their study added substantial data about catecholamine-mediated immuno-suppression, it lacked the identification of the adrenoceptor subtype involved in suppression of TLR9 signaling. We were able to identify ADRB2 as being the relevant adrenoceptor. However, we provide convincing evidence that ADRB2 is not expressed on pDCs. In agreement with this finding, we could only observe catecholamine-dependent pDC suppression when PBMCs other than pDCs were present. We would like to point out that Collado-Hidalgo enriched pDCs to about 40 and therefore always co-cultured them in the presence of contaminating PBMCs. While we believe their conclusion that norepinephrine exerts a direct effect on pDCs has to be questioned, their original data is actually in agreement with ours. Based on our own data, we propose two possible mechanisms for catecholamine-mediated pDC suppression within PBMCs: First, upon ADRB2 stimulation, PBMC subsets might release a humoral factor directly suppressing pDCs. This was shown to be the case for suppression of TLR9 signaling in pDCs by monocytes in the presence of bacterial cell wall products [3]. Furthermore, a whole set of surface receptors inhibiting IFNA1 release (e.g., Siglec-H, NKp44, BDCA2 and more) was recently identified on pDCs [1]. It is not known, whether these surface molecules have natural ligands they interact with. Second, IFNA1 release from pDCs is enhanced by PBMCs, presumably by cytokine signaling. This is in accordance with findings of other authors [31]. ADRB2 signaling could suppress these paracrine effects. Liu and colleagues demonstrated that activated pDCs are potential inducers of antitumor responses mediated by NK cells and T cells [7]. We used an in vitro assay to investigate possible effects of epinephrine on the modulation of NK cell- dependent tumor cell lysis by pDCs. While the addition of CpG ODN-treated cell culture supernatants enhanced tumor cell lysis, this effect was attenuated when the supernatant was taken from cells being coincubated with epinephrine and TLR9 ligands. Since direct effects of adrenoceptor stimulation on NK cell activity have been described [32], we added propranolol with cell culture supernatants in all cases to diminish direct effects of epinephrine on NK cells. Another key function of pDCs is the initiation of appropriate antiviral immune responses [1,4]. Collado-Hidalgo demonstrated that norepinephrine facilitates replication of HIV by suppression of type I interferon responses [30]. It is conceivable that similar effects will be observed in future studies of type I interferons, pDCs and their interplay with catecholamines. It is widely accepted knowledge that the neuroendocrine system modulates immune responses via its signaling molecules acetylcholine and (nor-) epinephrine. Pharmacological modifiers of these pathways are widely used in the clinical setting, especially duringBeta2-Adrenoceptors Suppress TLR9-Dependent IFNAFigure 5. Effect of ADRB2-mediated suppression of IFNA1 release on NK cell activity.