Neutrophils and redox stress in the pathogenesis of autoimmune disease.

Polymorphonuclear leukocytes, or neutrophils, are specialist phagocytic cells of the innate immune system. Their primary role is host defence against micro-organisms, which they kill via phagocytosis, followed by release of reactive oxygen species (ROS) and proteolytic enzymes within the phagosome. ROS are generated via the action of the NADPH oxidase (also known as NOX2), in a process termed the 'Respiratory Burst'. This process consumes large amounts of oxygen, which is converted into the highly-reactive superoxide radical O2- and H2O2. Subsequent activation of myeloperoxidase (MPO) generates secondary oxidants and chloroamines that are highly microbiocidal in nature, which together with proteases such as elastase and gelatinase provide a toxic intra-phagosomal environment able to kill a broad range of micro-organisms. However, under certain circumstances such as during an auto-immune response, neutrophils can be triggered to release ROS and proteases extracellularly causing damage to host tissues, modification of host proteins, lipids and DNA and dysregulation of oxidative homeostasis. This review describes the range of ROS species produced by human neutrophils with a focus on the implications of neutrophil redox products in autoimmune inflammation.

Patterned substrates fabricated by a controlled freezing approach and biocompatibility evaluation by stem cells.

Patterned substrates have been widely used in the studies investigating how to regulate cell growth and alignment. Such substrates may be fabricated by various techniques such as photolithography, soft lithography and microcontact printing. We report here a facile approach to fabricate aligned and grid surface patterns by a controlled freezing approach and further investigate their biocompatibility. The fabrication has been demonstrated with polymers (hydrophilic & hydrophobic), nanoparticles (organic & inorganic), or mixtures of these components. For the aligned surface patterns, the spacings between the patterned ridges can be tuned by varying the freezing rates. The biocompatibility of the substrates is evaluated by WST-8 viability tests with cell counting kit-8 (CCK-8) and by culturing with mouse mesenchymal stem cells (mMSCs). Three surface-patterned substrates (PLGA, PLGA nanospheres with chitosan, and silica colloids) are evaluated in more details to show that the mMSCs can grow alongside the aligned ridges while the cells grow randomly when plain glass slides are used as control. Further observations show that PLGA substrates undergo degradation, and are thus unsuitable for cell culture over the longer term. On the other hand, the PLGA-chitosan substrate and silica substrate were stable and could maintain mMSC alignment throughout the culture period.

Induction of mesenchymal stem cell chondrogenesis by polyacrylate substrates.

Mesenchymal stem cells (MSCs) can generate chondrocytes in vitro, but typically need to be cultured as aggregates in the presence of transforming growth factor beta (TGF-ß), which makes scale-up difficult. Here we investigated if polyacrylate substrates modelled on the functional group composition and distribution of the Arg-Gly-Asp (RGD) integrin-binding site could induce MSCs to undergo chondrogenesis in the absence of exogenous TGF-ß. Within a few days of culture on the biomimetic polyacrylates, both mouse and human MSCs, and a mesenchymal-like mouse-kidney-derived stem cell line, began to form multi-layered aggregates and started to express the chondrocyte-specific markers, Sox9, collagen II and aggrecan. Moreover, collagen II tended to be expressed in the centre of the aggregates, similarly to developing limb buds in vivo. Surface analysis of the substrates indicated that those with the highest surface amine content were most effective at promoting MSC chondrogenesis. These results highlight the importance of surface group functionality and the distribution of those groups in the design of substrates to induce MSC chondrogenesis.