It is clear that cells have adopted and developed several mechanisms that make it possible to internalize large solid particles as well as solutes and liquid substrates. In the current state of understanding, it is considered conventional to subdivide the process of phagocytosis on several specific activities of a living cell, namely: 1) pinocytosis, which represents a way to engulf bulks of liquid substrate and fluids; 2) phagocytosis itself is very similar to pinocytosis, with the only difference being that the phagosome contains solid particles; 3) receptor-mediated endocytosis, which provides the formation of phagolysosome involving specific uptake in a clathrin-dependant manner. Speaking of multicellular organisms, we can subdivide phagocytosis in compliance with the main types of targets, which are dying cells and, specifically, microbial pathogens alongside with other allogenic particles. Therefore, in this case, the main question, such as what is phagocytosis must be approached from a detached view of phagocytes’ functions that are, predominantly, control of immunological responses, eliminating inflammations, clearance of old and dying cells (which is connected with precise sensing and internalization) as well as maintenance of tissue homeostasis.
As opposed to writing a persuasive essay a well-written original research on a biological topic requires both a qualified coursework definition and thoroughly accumulated knowledge of the topic. Let us overlook a set of crucial terms and definitions that are widely accepted among modern immunology scientists. Hence, the core vocabulary includes the following items:
Generally speaking, a cell that is not undergoing any said death-related phenomenon can be competently considered viable. Today, electronic microscopy is thought to be the standard for determination of cell viability. Undoubtedly, EM has long become a routine procedure alongside with many even simpler and cheaper experimental methods. Other methods employing dyeing and chemical cell impregnation are also possible only after cell fixation and death (for instance, dyeing with trypan blue or propidium iodide). Nevertheless, there is no shortage of specialists who do a routine examination and careful monitoring of cellular processes using light microscopy alone or any other approaches that enable researchers to conduct the experiment without killing a cell culture. Regrettably, these techniques are often insensible to the early stages of PCD and, therefore, cannot be counted as universal or widely applicable.
It is highly important to remember that advantages of cell lines depend greatly on the degree of their invariance. Unquestionably, the precision of a laboratory experiment has little to do with religious studies, which means it is not possible for a researcher to keep faith in the purity of cell lines. One way or another, all cell lines must be assessed for accumulated mutations before enabling them into any laboratory procedure. This concerns lines of phagocytes in the first places. The terms non-professional and professional phagocytes are connected with a specific function of a cell; that is, the latter refers to dendritic cells and macrophages, while the former consists of cells that are primarily localized near the cell that dies. Depending on what site and current level of activity the given cell characterizes of it may get involved in different kinds of cell-to-cell interactions and perform variously under specific conditions.
First and foremost, a student should bear in mind before asking about how to write a coursework that the nature of apoptotic cells engulfed by professional phagocytes still remains an unresolved issue. Some researchers believe that those cells are, indubitably, a source of tolerogenic antigens. Moreover, this topic becomes especially controversial when it is a matter of tissue-specific autoantigens. Clearance of dying cells is the issue of the biggest concern for both neighboring accidental phagocytes and professional killer cells. However, it has become widely accepted that cells undergoing apoptosis could be a top-priority source of stimulatory autoantigens in case clearance is reduced, delayed or, for some reason, stopped. The term efferocytosis referring to the phagocytosis of apoptotic cells brings in even more subjects for a long-standing discussion. It seems, the characterization of the corresponding receptors as well as “calm” determinants on either an apoptotic cell or professional phagocyte will be practically indispensable for stable and substantive molecular progress.
The phenomenon of phagocytosis was first discovered by Russian scientist Ilya Ilyich Mechnikov and is a derivation from Greek words meaning “devouring cells”. On equal terms with Paul Ehrlich, I.I. Mechnikov was awarded the Nobel Prize in Physiology and Medicine in 1908. This highly important biological process was observed in transparent starfish larvae; mostly, the definition of phagocytosis given by contemporary science is still within the primary understanding – that is, we define phagocytosis as the process of engulfment and destruction of solid particles, which size exceeds 0.5 µm. As long as a student intends to compose a 500 word essay or a terse overview related to the phenomenon of phagocytosis, it will be useful for them to read and analyze original works by Mechnikov. Being significantly ahead of his time, the Russian immunologist managed to identify more or less fully a defensive function of phagocytes as well as provide a unique description of apoptotic cell clearance by macrophage and overlook the involvement of phagocytes in the degeneration of host cells by the example of tadpoles. Of course, the previous decades of scientific development have contributed a large amount of experimental data and now we can witness profound progress in understanding the molecular mechanisms and functional implementation of phagocytosis.
While simple and amoebae-like organisms use the phenomenon of phagocytosis to supply their cells (or a single cell) with nutrients and energy, larger and more complex organisms have specialized functions of their particular cells up to the level where they are known as professional phagocytes. Apart from those killer cells, there are also other – for instance, ladder epithelial cells – that can successfully perform clearance of junk cells or cellular debris under certain conditions. Simultaneously, professional killer cells, such as dendritic cells, neutrophils, and macrophages are irreplaceable for tissue defense and immune surveillance with the object to eliminate bacteria, fungi, infectious pathogens and other allogenic agents. Accordingly, the question what is phagocytosis starts, primarily, at the cellular level, albeit it is strongly related to molecular and genetic specificity. Basically, contemporary immunology is interested in recognizing receptors and specificity of phagocytosis above all. According to the most recent data, the direct interaction of an allogenic agent with the phagocyte is possible due to PRR (pattern recognition receptors) and specificity of this process has roots in pathogen’s conserved structural motifs. At the same time, another group of highly specific allogenic proteins that are known under the name of opsonins promotes the discovery of the opsonic receptors. For instance, the Fcγ receptor, which is connected to the immunoglobulin antibody, is responsible for phagocyte activation as well as complement receptors that were found on dendritic cells and macrophages.