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To evaluate positive/negative thresholds for serological tests, composite samples consisting of 200 potato‐tuber cores were extracted and tested for the presence of Clavibacter michiganensis subsp. sepedonicus by ELISA and immunofluorescence using specific monoclonal antibodies. Transformed ELISA absorbance values for ring rot‐infected tuber tissue diluted in 10‐fold increments in known negative composite sample extracts were fitted to a‘broken stick’nonlinear regression model. Of the 103 dilution series that were tested, 91% fitted the model with R2 > 0.98. The model consisted of a response and non‐response domain. The absorbance values in the non‐response domain, which served as estimates of background readings, ranged from 0.006 to 0.049. The values did not differ significantly among brands of ELISA plates used for between laboratories, and thus provided a reference point for setting a positive/negative threshold for the ELISA test. In the immunofluorescence test, 94% of composite samples from 1003 commercial seed lots had <1 immunofluorescing unit (IFU) per microscope field; only 1% of samples had >2 IFU per field. A positive/ negative threshold at 5IFU per field was considered to be appropriate for avoiding false positive readings.

Aortic valve stenosis (AS) development is driven by distinct molecular and cellular mechanisms which include inflammatory pathways. Toll-like-receptor-3 (TLR3) is a lysosomal pattern-recognition receptor that binds double-stranded RNA and promotes pro-inflammatory cellular responses. In recent years, TLR3 has emerged as a major regulator of vascular inflammation. The exact role of TLR3 in the development of AS has not been investigated. Isolated human valvular interstitial cells (VICs) were stimulated with the TLR3-agonist polyIC and the resulting pro-inflammatory and pro-osteogenic response measured. Severe AS was induced in wildtype- and TLR3−/− mice via mechanical injury of the aortic valve with a coronary springwire. TLR3 activation was achieved by polyIC injection every 24 h after wire injury, while TLR3 inhibition was realized using Compound 4a (C4a) every 48 h after surgery. Endothelial mesenchymal transition (EndoMT) of human valvular endothelial cells (VECs) was assessed after polyIC stimulation. Stimulation of human VICs with polyIC promoted a strong inflammatory and pro-osteogenic reaction. Similarly, injection of polyIC marginally increased AS development in mice after wire injury. AS induction was significantly decreased in TLR3−/− mice, confirming the role of endogenous TLR3 ligands in AS pathology. Pharmacological inhibition of TLR3 with C4a not only prevented the upregulation of inflammatory cytokines and osteogenic markers in VICs, and EndoMT in VECs, but also significantly abolished the development of AS in vivo. Endogenous TLR3 activation significantly contributes to AS development in mice. Pharmacological inhibition of TLR3 with C4a prevented AS formation. Therefore, targeting TLR3 may be a viable treatment option.

Background: Our current concept of aortic valve stenosis (AS) development suggests that local chronic inflammation drives fibrosis and calcification of the valve cusps. This remodeling is driven by endothelial to mesenchymal transition (EndMT) of valvular endothelial cells (VECs) and by calcification of valvular interstitial cells (VICs). In a preliminary screening, we found Toll-like receptor 3 (TLR3) expression increased in human AS samples. Therefore, aim of this study was to investigate the role of TLR3 in the pathogenesis of AS. Methods/Results: We confirmed TLR3 expression in cultured human VICs and VECs. Upon specific TLR3 stimulation with PolyI:C, both VICs and VECs displayed a positive feedback with increased TLR3 expression. Concomitant treatment of PolyI:C-stimulated VICs and VECs with the TLR3/RNA complex inhibitor (C4a) significantly blunted this response. Importantly, the TLR3-mediated pro-inflammatory and calcifying response of VICs and EndMT by VECs was significantly reduced by TLR3-inhibtion with C4a.To examine the role or TLR3 in AS development, a wire injury induced AS mouse model was used. Valves were explanted and stained with hematoxylin/eosin, Sirius red, von Kossa, or anti CD68. PolyI:C treatment promoted AS, as demonstrated by increased valve cusp thickness and pronounced valvular inflammation. Interestingly, AS development was nearly absent in TLR3 deficient mice suggesting a critical role of endogenous TLR3 ligands in this model. Treatment of mice with C4a after wire-injury of the aortic valve significantly reduced both morphological and functional parameters of AS development. Conclusion: These findings not only support the role of endogenous TLR3 activation in the development of AS but suggest that specific TLR3 inhibition might be beneficial for the treatment or prevention of AS. Further studies are required to decipher the exact mechanisms how TLR3 contributes to AS.

Background Aortic valve stenosis (AS) is the most common valve diseases in the western world. After having been considered a passive degenerative process, which develops as an inevitable consequence of age-related valvular degeneration, basic research of the last two decades has led to a paradigm shift. It is now believed that AS pathophysiology is driven by distinct molecular and cellular mechanisms which include inflammatory pathways. In recent years, Toll-like-receptor-3 (TLR3) has emerged as a major regulator of vascular inflammation. TLR3 is a lysosomal pattern recognition receptor that recognizes single and double stranded RNA. Its activation leads to expression of pro-inflammatory cytokines via NFkb activation. The role of TLR3 in the development of AS has never been investigated. Methods Severe AS was induced in Wildtype-, ApoE- and TLR3/ApoE−/− mice. For this, a coronary springwire was used to induce an endothelial injury under echocardiographic guidance. Stenosis development was confirmed via ultrasound examinations. To inhibit TLR-3 activation, TLR3/RNA- Complex inhibitor C4a was injected every 48h after wire injury in WT mice. Valves were explanted and stained with hematoxylin/eosin (valve thickening) or anti-68 (macrophage infiltration). Valves from patients who received aortic valve replacement due to AS or aortic regurgitation (AR) were collected and mRNA levels of TLR3 and MyD88 were measured with use of quantitative-PCR. Results To evaluate weather TLR3 effects AS development in mice, we subjected TLR3/ApoE double- and ApoE knockout mice to our model of wire-induced AS. Surprisingly, TLR3 deficient mice failed to develop AS after wire injury. Peak velocity measurements showed no increase and histological analysis showed lower aortic valve area and macrophage infiltration compared to control mice. In order to pharmacological inhibit TLR3, WT mice were treated with C4a after wire injury. Compared to PBS control, C4a mice also did not develop AS upon wire injury. Trans-aortic valve peak velocity levels were significantly lower in C4a mice. Histological analysis underlined these results and showed thinner aortic valves and decreased macrophage infiltration in C4a mice comparted to control animals. To confirm our hypothesis, the expression of TLR3 and its downstream effector MyD88 were measured in human aortic valve specimens. qPCR analysis revealed decreased TLR3 and MyD88 expression in patients with AS compared to patients with AR. Conclusion In the presented study, we present first data that theTLR3 has a crucial role in the development of AS in mice. The exact downstream effects after TLR3 activation in AS need to be further investigated. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)