ER stress in antigen‐presenting cells promotes NKT cell activation through endogenous neutral lipids

CD1d-restricted invariant natural killer T (iNKT) cells constitute a common glycolipid-reactive innate-like T-cell subset with a broad impact on innate and adaptive immunity. While several microbial glycolipids are known to activate iNKT cells, the cellular mechanisms leading to endogenous CD1d-dependent glycolipid responses remain largely unclear. Here, we show that endoplasmic reticulum (ER) stress in APCs is a potent inducer of CD1d-dependent iNKT cell autoreactivity. This pathway relies on the presence of two transducers of the unfolded protein response: inositol-requiring enzyme-1a (IRE1α) and protein kinase R-like ER kinase (PERK). Surprisingly, the neutral but not the polar lipids generated within APCs undergoing ER stress are capable of activating iNKT cells. These data reveal that ER stress is an important mechanism to elicit endogenous CD1d-restricted iNKT cell responses through induction of distinct classes of neutral lipids

Evolution and function of the epithelial cell-specific ER stress sensor IRE1β

Barrier epithelial cells lining the mucosal surfaces of the gastrointestinal and respiratory tracts interface directly with the environment. As such, these tissues are continuously challenged to maintain a healthy equilibrium between immunity and tolerance against environmental toxins, food components, and microbes. An extracellular mucus barrier, produced and secreted by the underlying epithelium plays a central role in this host defense response. Several dedicated molecules with a unique tissue-specific expression in mucosal epithelia govern mucosal homeostasis. Here, we review the biology of Inositol-requiring enzyme 1β (IRE1β), an ER-resident endonuclease and paralogue of the most evolutionarily conserved ER stress sensor IRE1α. IRE1β arose through gene duplication in early vertebrates and adopted functions unique from IRE1α which appear to underlie the basic development and physiology of mucosal tissues

IRE1β negatively regulates IRE1α signaling in response to endoplasmic reticulum stress

IRE1β is an ER stress sensor uniquely expressed in epithelial cells lining mucosal surfaces. Here, we show that intestinal epithelial cells expressing IRE1β have an attenuated unfolded protein response to ER stress. When modeled in HEK293 cells and with purified protein, IRE1β diminishes expression and inhibits signaling by the closely related stress sensor IRE1α. IRE1β can assemble with and inhibit IRE1α to suppress stress-induced XBP1 splicing, a key mediator of the unfolded protein response. In comparison to IRE1α, IRE1β has relatively weak XBP1 splicing activity, largely explained by a nonconserved amino acid in the kinase domain active site that impairs its phosphorylation and restricts oligomerization. This enables IRE1β to act as a dominant-negative suppressor of IRE1α and affect how barrier epithelial cells manage the response to stress at the host–environment interface

Relevance of single channel signals for two-colour pyrometer process monitoring of laser powder bed fusion

This paper discusses the relevance of two-colour pyrometers' single channel signals for process monitoring of laser powder bed fusion metal additive manufacturing. First, examples are presented where the ratio temperature provided by the pyrometer is misleading. Following is a demonstration that such instances can be uncovered by the single channel signals, where an approach for simplified signal analysis based on the working principles of the pyrometer is provided. In closing, a validation is implemented, where the careful inspection and employment of the single channel signals yielded suitable input for a successful closed-loop process control.ISSN:1753-1039ISSN:1753-104

Surface quality improvement and adjustment of SLM-processed CM247LC samples by modulated laser parameters

Nickel-base alloys, such as “CM247LC”, are usually used in the aviation field to manufacture high-pressure turbine blades with cooling channels, to increase the turbine entry temperature and the efficiency. Since there are many different cooling strategies for turbine blades, the requirements for the surface parameters (e.g. surface roughness) vary highly. In this study, five different surface parameters, such as root mean square height, skewness, kurtosis, developed interfacial area ratio and texture aspect ratio with different modulated laser parameters, have been measured, analyzed, plotted as diagrams and compared with reference continuous wave SLM-produced samples. Process maps with an overall surface parameter (including all five parameters) are also presented. Results show a wide range of surface parameter values, as needed for the varying surface requirements of different blade cooling systems.ISSN:2212-827

Residual stress reduction of LPBF-processed CM247LC samples via multi laser beam strategies

Based on SLM parameters from previous works, which guarantee fully dense and crack free CM247LC samples, multi laser beam strategies have been pursued to reduce residual stresses or rather distortion during LPBF processing. By using a second post heating and non-melting laser source with a defocused laser beam and lateral offset, cantilever distortion is reduced more than 7.5%, compared to the reference. Based on pre-tests with 9 different offset parameters, the optimum offset has been identified. Also, an upper limit for the laser power of 65 W is identified for the second heat laser beam with a spot diameter of 380 μm, to avoid re-melting and creating new defects. A theoretical “two bar model,” to explain the residual stress behavior and reduction with multi laser beam offset strategy during the LPBF process, is presented. Furthermore, re-melting cracks, defects, and microstructure are analyzed in conjunction with the second defocused offset laser, in case of a 200 W laser power, an increased scan speed of 1300 mms/s, and a reduced hatch distance. Secondary electron signal (SE) images of re-melting cracks are analyzed and compared to SE-image of hot cracks (solidification cracks). Based on electron backscatter diffraction (EBSD), the results of the microstructure from the last mentioned multi laser beam approach, which creates re-melting cracks, are presented and analyzed.ISSN:0268-3768ISSN:1433-301

Focus shift analysis, to manufacture dense and crack-free SLM-processed CM247LC samples

Nickel-base alloy CM247LC is particularly sensitive for weld-cracking during powder-bed fusion, caused by an inappropriate laser spot diameter due to focus shifting. In this paper, the influence of a 4 mm focus shift on the melt pool geometry, intensity, relative Archimedean density, crack density, microstructure and texture is investigated, by using two different calibration procedures for the laser system. The hot calibration method is a procedure to overcome the thermally induced focus shift of 4 mm by setting the focus plane 4 mm below the build plane. After heating up to the operating temperature of the laser system by scanning two times an area of 10 x 10 mm², a stable focus diameter in the build plane is guaranteed. This procedure enables fully dense and crack-free CM247LC samples. Due to deeper melt pools, realized by higher intensity and a reduced laser beam diameter in the focus plane, the cracks in the layers below are re-molten and crack healing occurs. Between the cold and hot calibration procedure, the crack-density has been reduced relatively more than 98-times. Therefore, the laser beam diameter has been identified as an essential SLM parameter for healing hot cracks. Samples, which are manufactured with the hot calibrated system, indicate a stronger texture parallel to the build direction, compared to the cold calibrated one. Furthermore, Archimedean density, the lack of bonding and the porosity have been analyzed with varying laser scan speeds for the thermal steady state system. The increased Archimedean density correlates well with the decreased lack of bonding and porosity.ISSN:0924-013