Progressive enhancement of kinetic proofreading in T cell antigen discrimination from receptor activation to DAG generation.

T cells use kinetic proofreading to discriminate antigens by converting small changes in antigen-binding lifetime into large differences in cell activation, but where in the signaling cascade this computation is performed is unknown. Previously, we developed a light-gated immune receptor to probe the role of ligand kinetics in T cell antigen signaling. We found significant kinetic proofreading at the level of the signaling lipid diacylglycerol (DAG) but lacked the ability to determine where the multiple signaling steps required for kinetic discrimination originate in the upstream signaling cascade (Tiseher and Weiner, 2019). Here, we uncover where kinetic proofreading is executed by adapting our optogenetic system for robust activation of early signaling events. We find the strength of kinetic proofreading progressively increases from Zap70 recruitment to LAT clustering to downstream DAG generation. Leveraging the ability of our system to rapidly disengage ligand binding, we also measure slower reset rates for downstream signaling events. These data suggest a distributed kinetic proofreading mechanism, with proofreading steps both at the receptor and at slower resetting downstream signaling complexes that could help balance antigen sensitivity and discrimination.

ToF-SIMS and TIRF microscopy investigation on the effects of HEMA copolymer surface chemistry on spatial localization, surface intensity, and release of fluorescently labeled keratinocyte growth factor.

The need for direct biomaterial-based delivery of growth factors to wound surfaces to aid in wound healing emphasizes the importance of interfacial interactions between the biomaterial and the wound surface. These interactions include the spatial localization of growth factor, the surface intensity of growth factor in contact with the wound, and the release profile of growth factor to the wound surface. The authors report the use of time-of-flight secondary ion mass spectrometry to determine the relationship between biomaterial surface chemistry and the spatial localization of growth factor. They have implemented a novel application of total internal reflectance fluorescence (TIRF) microscopy to measure the surface intensity and release of growth factor in contact with a glass substrate that has been used to model a wound surface. Detailed information regarding TIRF experiments has been included to aid in future studies regarding the biomaterial delivery to interfaces. The authors have evaluated the effects of (hydroxyethyl)methacrylate (HEMA) homopolymer, 5.89% methyl methacrylate/HEMA, and 5.89% methacrylic acid/HEMA surface chemistry on the spatial localization of AlexaFluor 488-labeled keratinocyte growth factor (AF488-KGF), AF488-KGF surface intensity at the copolymer surface, and release to a glass substrate. KGF is known to promote re-epithelialization in wound healing. The results show that the two copolymers allow for increased surface coverage, surface intensity, and release of AF488-KGF in comparison to the homopolymer. It is likely that differences in these three aspects could have a profound effect on the wound healing response.