Advanced microscopy and imaging techniques in immunology and cell biology

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The first widespread description of optical microscopes can be found referenced in literature around the thirteenth century. Since then, much like the space race that began in the 1950s, researchers have been relentlessly pushing the boundaries of microscope and imaging technology in the quest for higher spatial resolution, a wider spectral array of colours, deeper penetration into samples, faster acquisition times, all with the added level of difficulty of multipurpose use in fixed tissue, live cells and even whole living organisms. The advantage of microscopy is the vast information of dynamic lineage tracing and spatio-temporal information it provides. Thus, advanced microscopy has enabled us to understand immunology and cell biology from sub-cellular structure via super-resolution techniques to in situ function at the system level via intravital microscopy (IVM), and even clinical diagnosis of disease in patients. However, this level of information does come at a trade-off that analysis is far from standardised and often laborious.
In this Special Feature of Immunology & Cell Biology, we present a collection of reviews that discuss past and present approaches in microscopy that influence how we ‘literally’ view cell biology. We also look to the future at advances in hardware necessary to address questions currently just out of the reach of biologists and the demands this will place on computational and quantitative analysis.
Currently, we have vast methodologies that allow analysis of immune cell biology at the population level. However, the strength of microscopy is its ability to complement these studies by allowing interactions at the sub-cellular level to be visualised and, additionally, directly track the influence these events can have on cell fate at the single-cell level. This approach has been extremely useful in the study of T-cell biology where super-resolution techniques (such as TIRF, SIM, STORM and PALM) have allowed the components of the immunological synapse and T-cell receptor signalling to be dissected at the single-molecule level.1 Thus, from these studies we now have a previously unattainable understanding of dynamic cell-cell interactions during immune responses including T-cell activation and effector function. Importantly, the scalability of microscopy means that through long-term in vitro time-lapse studies, the direct influence of these events on immune cell expansion, fate diversification and effector function can be determined at the single-cell level.1 These studies have heavily influenced our understanding of fundamental T-cell and B-cell biology. This is especially relevant for lymphocyte lineage commitment, where it is now apparent that even in the presence of polyclonal activating signals, the diversity observed at the population level is a result of homogenous outcomes of daughter cells inherited from individual founder immune cells.
In vitro time-lapse studies have been crucial for developing reductionist systems to understand the foundations of cell biology. However, these approaches have always endured some level of criticism for their obvious inability to completely recapitulate the environment of a living organism. Thus, the ability to directly observe cells in situ through advances in IVM has provided a revolution in our understanding of cell biology. In this Special Feature, the surprisingly long history of IVM is discussed,2 including an introduction to the vast array of organs (and their associated cell types) that are now accessible for imaging. This discussion highlights the synergy between engineering and microscopy in an almost ‘MacGyver style’ practical approach to develop imaging platforms in an organ specific manner. For example, developing bespoke imaging braces and optical windows to secure organs for IVM via 3D printing technology.
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