Reduced Numbers and Impaired Function of Regulatory T Cells in Peripheral Blood of Ischemic Stroke Patients

Background and Purpose. Regulatory T cells (Tregs) have been suggested to modulate stroke-induced immune responses. However, analyses of Tregs in patients and in experimental stroke have yielded contradictory findings. We performed the current study to assess the regulation and function of Tregs in peripheral blood of stroke patients. Age dependent expression of CD39 on Tregs was quantified in mice and men. Methods. Total FoxP3+ Tregs and CD39+FoxP3+ Tregs were quantified by flow cytometry in controls and stroke patients on admission and on days 1, 3, 5, and 7 thereafter. Treg function was assessed by quantifying the inhibition of activation-induced expression of CD69 and CD154 on T effector cells (Teffs). Results. Total Tregs accounted for 5.0% of CD4+ T cells in controls and <2.8% in stroke patients on admission. They remained below control values until day 7. CD39+ Tregs were most strongly reduced in stroke patients. On day 3 the Treg-mediated inhibition of CD154 upregulation on CD4+ Teff was impaired in stroke patients. CD39 expression on Treg increased with age in peripheral blood of mice and men. Conclusion. We demonstrate a loss of active FoxP3+CD39+ Tregs from stroke patient’s peripheral blood. The suppressive Treg function of remaining Tregs is impaired after stroke

Impact of sulfur addition on the structure and dynamics of Ni-Nb alloy melts

We investigated the change in the structure and dynamics of a Ni–Nb bulk metallic glass upon sulfur addition on both microscopic and macroscopic scales. With the sulfur concentration of 3 at. %, where the composition Ni58Nb39S3 exhibits the best glass forming ability in the investigated sulfur concentration range, both the equilibrium and undercooled melt dynamics remain almost unchanged. Only in the glassy state does sulfur seem to result in mass transport less decoupled to the viscosity of the undercooled liquid, where the measured Ag tracer diffusion coefficient is slower in the ternary alloy. With the structural disorder introduced by the alloying sulfur, the improved glass forming ability is attributed to geometrical frustration, where crystal nucleation requires a depletion of sulfur and hence long range diffusion, as long as no primary sulfur-containing crystalline phase is involved

Impact of minor sulfur additions on the structure and dynamics of Ni-Nb melts

Bulk metallic glasses feature an amorphous structure, which results in exceptional properties as engineering materials. Typically alloying additional components improves the glass forming ability (GFA). Beside adding non-metallic elements like P, B, C, recently sulfur has been found to facilitate bulk metallic glasses formation at different concentration levels [1]. This makes them promising candidates for commercialization, where the alloy composition can be tuned according to applications. In the case of the binary Nig2Nb3g glass forming alloy, it has been found that an optimal enhancement of the GFA can be achieved by alloying only 3 at% S. Such kind of minor alloying effects cannot be understood by applying the common empirical rules like a denser packing of the melt, or the formation of deep eutectic compositions. Employing electrostatic levitation combined with in-situ synchrotron diffraction, we studied impacts of sulfur on the structure and dynamics of Ni-Nb based alloys, as well as on the solidification behavior from undercooled melt. First results show that small, but notable changes can be observed in the measured liquid structure factor upon an addition of 3 at% S. In particular, in the obtained X-ray total structure factor the position of the first structure factor maximum appears to shift towards lower g values. The structure changes are analyzed with the help of the partial structure factors of the binary Ni-Nb alloy [2]. It has been also observed that the initial phases solidified from the undercooled melt seem to be different with and without S. The implication of these changes on the glass forming behavior is discussed together with the melt viscosity measured using the oscillating drop technique. References: [1] A. Kuball, O. Gross, B. Bochtler, R. Busch, Scr. Mater. 146, 73-76 (2018). [2] D. Holland-Moritz, F. Yang, J. Gegner, T. Hansen, M. D. Ruiz-Martin, and A. Meyer, J. Appl. Phys. 115, 203509 (2014)

Fe isotope composition of bulk chondrules from Murchison (CM2): Constraints for parent body alteration, nebula processes and chondrule-matrix complementarity

Iron isotope compositions of bulk chondrules are so far only known from few studies on CV and some ordinary chondrites. We studied 38 chondrules from the CM chondrite Murchison. This is in particular challenging, as CM chondrites contain the smallest chondrules (av. diameter: 149 μm) of all chondrite groups, except for CH chondrites. Bulk chondrules have δ56Fe between -0.62 and +0.24‰ relative to the IRMM-014 standard. Bulk Murchison has as all chondrites a δ56Fe of 0.00‰. The δ56Fe distribution of the Murchison chondrule population is continuous and close to normal. The width of the δ56Fe distribution is narrower than that of the Allende chondrule population. Opaque modal abundances in Murchison chondrules is in about 67% of the chondrules close to 0 vol%, and in 33% typically up to 6.5 vol.%. Chondrule element ratios of Al/Mg´and Fe/Mg are sub-chondritic, while bulk Murchison has chondritic ratios. No correlations exist between Ni/Mg and modal abundance of opaque phases,possibly because opaque phases were oxidised during parent Body alteration. Initially maybe larger variations of bulk chondrule Fe isotope compositions may have been reduced during parent body alteration. Variable bulk chondrule Fe isotope compositions were established during evaporation and re-condensation prior to accretion in the Murchison parent body. Variable bulk chondrule Fe isotope compositions and a chondritic bulk Murchison, together with complementary element compositions, while bulk Murchison is chondritic, support the idea that chondrules and matrix formed from a single reservoir and were then accreted in the parent body. The formation in a single region also explains the compositional distribution of the chondrule population in Murchison

Magnetic Transitions in the Co-Modified Mn2Sb System

Mn2Sb is ferrimagnetic below its Curie temperature (TC) and passes through a spin flip transition with decreasing temperature. The Co substitution induces an additional first-order phase transition from the ferrimagnetic (FRI) to an antiferromagnetic (AFM) state. This phase transition is connected to a sizable magnetocaloric effect (MCE). To understand the underlying mechanisms, the temperature dependence of structural and magnetic changes was analyzed. At the same time, the influence of the Co substitution was explored. Three Mn2−xCoxSb (x = 0.1, 0.15, 0.2) compounds were synthesized by cold crucible induction melting. Neutron powder diffraction was performed to determine the magnetic structures and to obtain the individual magnetic moments on both symmetrically independent Mn sites. In combination with the temperature-dependent magnetization measurements, the magnetic phase transition temperatures were identified. In the low-temperature range, additional antiferromagnetic peaks were detected, which could be indexed with a propagation vector of (0 0 ½). In Mn1.9Co0.1Sb at 50 K and in Mn1.8Co0.2Sb at 200 K, a co-existence of the FRI and the AFM state was observed. The pure AFM state only occurs in Mn1.8Co0.2Sb at 50 K