Estimation of the effectiveness factor of an outer-sphere redox couple (Fe3+/Fe2+) using rotating disk Ti/IrO2 electrodes of different loading

The effectiveness factor; E f , defined as the fraction of the surface that participates effectively in a given reaction, is an important parameter when operating three-dimensional (3D) electrodes. The rotating disk electrode (RDE) technique with the Fe3+/Fe2+ redox couple as a probe reaction has been used for the evaluation of the effectiveness factor of 3D Ti/IrO2 electrodes with different IrO2 loading. For this purpose, steady-state polarization measurements using Ti/IrO2 rotating disk electrodes in 0.5M Fe3+/Fe2+ in 1M HCl were carried out under well-defined hydrodynamic conditions. The low-field approximation relation has been used for the estimation of the exchange current densities j 0, of the Fe3+/Fe2+ redox couple. It was found for this redox couple that the effectiveness factor is very low (<2%) and essentially the 2D electrode surface area works effectively in the steady-state polarization measurement

Effectiveness factor of fast (Fe3+/Fe2+), moderate (Cl2/Cl−) and slow (O2/H2O) redox couples using IrO2-based electrodes of different loading

The effectiveness factor, E f, (fraction of the electrode surface that participates effectively in the investigated reaction) of fast (Fe3+/Fe2+), moderate (Cl2/Cl−) and slow (O2/H2O) redox couples has been estimated using IrO2-based electrodes with different loading. The method of choice was linear sweep voltammetry (measurement of the anodic peak current) for the Fe3+/Fe2+ redox couple and steady-state polarization (determination of the exchange current) for the O2 and Cl2 evolution reactions. The results have shown that the effectiveness factor depends strongly on the kinetics of the investigated redox reaction. For the Fe3+/Fe2+ redox couple, effectiveness factors close to zero (max 4%) have been obtained contrary to the O2 evolution reaction where effectiveness factors close to 100% can be achieved, all being independent of IrO2 loading. For the Cl2 evolution reaction, intermediate values of the effectiveness factor have been found and they decrease strongly, from 100% down to about 60%, with increasing loadin

Effectiveness factor of fast (Fe3+/Fe2+), moderate (Cl2/Cl−) and slow (O2/H2O) redox couples using IrO2-based electrodes of different loading

International audienceThe effectiveness factor, E f, (fraction of the electrode surface that participates effectively in the investigated reaction) of fast (Fe3+/Fe2+), moderate (Cl2/Cl−) and slow (O2/H2O) redox couples has been estimated using IrO2-based electrodes with different loading. The method of choice was linear sweep voltammetry (measurement of the anodic peak current) for the Fe3+/Fe2+ redox couple and steady-state polarization (determination of the exchange current) for the O2 and Cl2 evolution reactions. The results have shown that the effectiveness factor depends strongly on the kinetics of the investigated redox reaction. For the Fe3+/Fe2+ redox couple, effectiveness factors close to zero (max 4%) have been obtained contrary to the O2 evolution reaction where effectiveness factors close to 100% can be achieved, all being independent of IrO2 loading. For the Cl2 evolution reaction, intermediate values of the effectiveness factor have been found and they decrease strongly, from 100% down to about 60%, with increasing loading

Tc17 Cells Mediate Vaccine Immunity against Lethal Fungal Pneumonia in Immune Deficient Hosts Lacking CD4⁺ T Cells

<div><p>Vaccines may help reduce the growing incidence of fungal infections in immune-suppressed patients. We have found that, even in the absence of CD4⁺ T-cell help, vaccine-induced CD8⁺ T cells persist and confer resistance against <em>Blastomyces dermatitidis</em> and <em>Histoplasma capsulatum</em>. Type 1 cytokines contribute to that resistance, but they also are dispensable. Although the role of T helper 17 cells in immunity to fungi is debated, IL-17 producing CD8⁺ T cells (Tc17 cells) have not been investigated. Here, we show that Tc17 cells are indispensable in antifungal vaccine immunity in hosts lacking CD4⁺ T cells. Tc17 cells are induced upon vaccination, recruited to the lung on pulmonary infection, and act non-redundantly in mediating protection in a manner that requires neutrophils. Tc17 cells did not influence type I immunity, nor did the lack of IL-12 signaling augment Tc17 cells, indicating a distinct lineage and function. IL-6 was required for Tc17 differentiation and immunity, but IL-1R1 and Dectin-1 signaling was unexpectedly dispensable. Tc17 cells expressed surface CXCR3 and CCR6, but only the latter was essential in recruitment to the lung. Although IL-17 producing T cells are believed to be short-lived, effector Tc17 cells expressed low levels of KLRG1 and high levels of the transcription factor TCF-1, predicting their long-term survival and stem-cell like behavior. Our work has implications for designing vaccines against fungal infections in immune suppressed patients.</p> </div

Role of IL-12 signaling on vaccine-induced Tc1 and Tc17 cells and resistance against fungal pneumonia.

<p>Mice were depleted of CD4⁺ T cells, vaccinated and challenged as described in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1002771#ppat-1002771-g002" target="_blank">Fig. 2</a>. <b>A.</b> Three weeks after challenge, lung CFU were enumerated. CFUs are depicted in box and whisker plots for 10–17 mice/group. Data is representative of two independent experiments. <b>B.</b> On day 3–4 post-challenge, lungs were collected to enumerate cytokine producing CD8⁺ T cells by flow cytometry. <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1002771#s2" target="_blank">Results</a> are the mean ± SD of 4–8 mice/group from two independent experiments. *, p<0.05 vs. unvaccinated mice; and **, p<0.01.</p

Non-redundant role of Tc17 cells in anti-fungal vaccine immunity.

<p>Mice were vaccinated with 10⁵ yeast of <i>Blastomyces</i> vaccine strain #55 subcutaneously (s.c.) and boosted once after 2 weeks. Two to three weeks later, mice were challenged intratracheally (i.t.) and lungs were harvested to enumerate CFUs. CD4⁺ T cells were depleted with GK1.5 mAb given i.v. weekly. <b>A.</b> Mice were given neutralizing anti-IL-17A mAb or rat IgG as control (100 µg each, i.v.) on days 0, 2 & 4 post-challenge. On day 6, lungs were analyzed for CFU. CFUs are from 8–14 mice/group. <b>B.</b> On day −3 and −1, mice were given 2–4×10⁹ pfu i.v. of recombinant adenovirus secreting mouse IL-17 receptor or control adenovirus expressing luciferase (AdLuc); a third dose was given on day 0 of challenge with virulent <i>Blastomyces</i> (i.t.). 10 days after challenge, lungs were harvested for CFU. CFUs are for 13–19 mice/group. <b>C.</b> IL-17RA^−/− and WT mice were infected i.t. with a lethal dose of WT <i>Blastomyces</i> yeast. 10 days later, lung CFU were enumerated. CFUs are from 10–14 mice/group from two independent experiments. <b>D.</b> IL-17A^−/− and WT mice were lethally challenged i.t. with WT <i>Blastomyce</i>s yeast. 13 days later, lung CFU were enumerated. CFUs are from 9–19 mice/group. In panels A–D, CFUs are shown in box and whisker plots. *, p<0.05; **, p<0.01; ***, p<0.001; and ****, p<0.0001.</p

CCR6 mediated recruitment of Tc17 cells into the lung after challenge.

<p>Mice were depleted of CD4⁺ T cells and vaccinated as described in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1002771#ppat-1002771-g002" target="_blank">Fig. 2</a>. <b>A.</b> Dot plots show the frequency of CCR6⁺ or CXCR3⁺ cells (middle and right panels) gated on the respective cytokine producing CD8⁺ T cells (left panel) in the dLNs after vaccination. <b>B.</b> Dot plots show the frequency of CCR6⁺ or CXCR3⁺ Tc17 cells (middle and right panels, respectively) in the lung 4 days after pulmonary challenge. <b>C.</b> The number of cytokine producing CD8⁺ T cells in the lung 5 days after pulmonary challenge as measured by flow cytometry. For neutralization of CCL20, vaccinated mice were given ∼90 µg of α-mouse CCL20 mAb or control antibody i.v. on days 0, 2 and 4 post-challenge. Values are mean ± SD of 5–6 mice/group. *, p<0.05.</p