Shine a light: Imaging the immune system

Abstract

Intra vital microscopy and whole-body imaging promise to revolutionize how we study the immune system. They compel by the intrinsic beauty of the images obtained and the undeniable direct biological relevance of the observations. However, it is important to remember that in many cases, fundamental insights into the underlying biological processes have already been obtained using ex vivo reductionist approaches. Indeed, it is likely that with the advent of microfluidics, new and exciting avenues will open up for ex vivo experimentation. Here, we give a brief but comprehensive overview of the various imaging techniques available, their relative strengths and shortcomings and how these tools have been used to get us to where we are today. The challenge for the future will be to apply the most suitable technology and to integrate the findings across various imaging disciplines to build a unified, comprehensive ''big picture'' of the immune system.Key words: Imaging . Microscopy . Technology During a comparative study of digestive organs, Elie Metchnikoff was intrigued by the fact that certain cells that play no role in digestion, nevertheless have the ability to ingest foreign bodies [1]. The ''model system'' he used to study this phenomenon was the starfish larva, which is transparent enough to observe individual cells moving within. Metchnikoff observed that when he inserted a small splinter into the larvae, some cells accumulated at the point of insult and tried to ingest the foreign body. He had discovered phagocytosis, a phenomenon he demonstrated to be ubiquitous throughout the Animal Kingdom [2]. As higher organisms were not suited to direct microscopic examination, Metchnikoff proceeded to isolate phagocytic cells from the blood of higher organisms and demonstrated that these cells ingest and destroy microorganisms. Based on his observation, he introduced the concept of cellular immunity. Thus, it is fair to say that microscopic imaging has always been at the center of immunological research from its very conception. Initially however, immunologists had no tools with which to observe the cells involved in immune responses in higher organisms in vivo. They could use either tissue sections to reconstitute what had happened from snapshots or they could study specific aspects of the immune response with isolated cell populations ex vivo. The contributions of tissue imaging in immunology over the past century have been recently reviewed [3]. Here, we provide a broad overview of the multitude of imaging approaches that have been applied in immunology, ranging from ex vivo single molecule detection to in vivo whole-body imaging and microfluidic ''lab on a chip'' technology for immunological studies. Ex vivo studiesMany of the functions of the immune system can be mimicked ex vivo using primary cell populations. Early separation techniques relied on the physical characteristics of the cells. Velocity sedimentation was used to sort the cells according to size [4] and differential adherence in order to separate subpop...

Systems Biology in Immunology: A Computational Modeling Perspective

“…More examples and a detailed review of modern microscopic technologies used for imaging the immune system can be found in (283). Here we highlight some examples of the applications of the instruments and techniques mentioned above.…”

Imaging immunity

“…The array of microscopic techniques currently used to study immunology has recently been comprehensively summarized in an excellent review by Sarris and Betz [1]. Our report here will try to avoid too much overlap with this review.…”

Advances in three-dimensional rapid prototyping of microfluidic devices for biological applications

“…Microfluidics also offer the means to create and maintain environments that closely resemble those encountered in vivo. 40,41 This is essential in ensuring that the experimental results are not biased with artefacts caused by, for example, early triggered apoptosis and, therefore, creating the right environment has important implications in cell analysis. Moreover, current microfabrication techniques allow the production of large arrays of microwells that can entrap single/multiple cells to perform molecular analysis, 42 or study cell response to chemical and physical stimuli following exposure to different environments; 43 the major advantage of this approach being the ability to perform parallel screening of a large number of cells.…”