Biomedical Science Tissue-resident Macrophages.

Question: Discuss about the Biomedical Science for Tissue-resident Macrophages. Answer: Introduction Macrophages are professional phagocytes. They are tissue resident and originate from monocytes, which are produced by the stem cells in the bone marrow (Epelman et al. 2014). Monocytes usually move out of the blood capillaries through the endothelium, by the process of diapedesis or leukocyte extravasations in response to infection or tissue damage. It then goes through a sequence of changes, to form a macrophage. The movement of monocytes towards a site of infection or damage is initiated by release of chemical substances at the site, which attracts the monocytes through chemotaxis. Definition Macrophages is a phagocytic tissue cell of the invulnerable framework that might be altered or unreservedly motile, is derived from a monocytes, capacities in the decimation of outside antigens (as microscopic organisms and infections), and serves as an Antigen Presenting Cells. In short they are big eaters. (Greek word: makros- Large + phagein- eat). Functions They play an important role in both adaptive and innate immunity. They are extensive, biosynthetically dynamic cells with intense endocytic, phagocytic, and secretory capacities, ready to balance their properties upon contact with various cell sorts and additionally extracellular lattice (Fejer and Gyory 2015). Macrophages are strikingly flexible in their capacity to perceive and react to an extensive variety of stimuli, communicating an assortment of surface and intracellular receptors, different sign transduction pathways and varieties of quality expression (Davies et al. 2013). Their inherent heterogeneity amid separation is intensified by corresponding cooperations with neighbouring cells, including macrophages themselves, different microorganisms, sterile particulates and dissolvable mediators (Fejer et al. 2013). Macrophages control activation of lymphocyte as well as their proliferation; they are also responsible in activating B and T- lymphocytes. They are also known as antigen presenting cells or APCs, which present antigens to T- lymphocytes after digesting microbes (Fejer and Gyory 2015). Macrophage and monocytes both are secretory in nature and release monokines, complement proteins and factors such as interleukin-1, such cells are known as activated macrophages (Davies et al. 2013). Macrophages also aid in muscle cell regeneration by two major groups. When the muscle tissue is damaged considerably, an influx of these phagocytic cells occur, which demolish and degrade the injured muscle fibres. A second group of macrophages, which are not phagocytic in nature, enables regeneration of muscle fibres (Yona et al. 2013). Type of macrophage Heterogeneity Macrophages are classified under mononuclear phagocyte system, which includes the phagocytic cells of the reticulo-endothelial system. The mononuclear phagocyte system is a major constituent of cell-mediated and humoral immunity. Interactions between pathogen and macrophages were studied using mice model, because of the accessibility of inbred strains. These studies gave a clear understanding of irresistible infections and the atomic system behind it (Davies et al. 2013). Self renewing macrophage system There are self renewing macrophage system under homeostatic condition include self renewal of tissue resident macrophages and self renewing macrophages during inflammation (Fejer et al. 2015). Refer to Appendix for figure. Heterogeneity of macrophages The macrophages are developed from monocytes circulating within the blood stream and display a very high level of heterogeneity, which has been revealed through extensive studies with monoclonal antibodies (Locati and Sica 2012). Usually monocytes show Epelman et al. 2014diversification in morphology of nucleus, size and granularity. Tissue macrophages on the contrary exhibit heterogeneity based on functions that differ according to their occurrence. For example, the osteoclasts found in bone tissue are responsible for tissue remodelling of bones, and pattern recognition receptors in alveolar macrophages, which help in cleaning the lung tissue by removal of pathogens (Fejer and Gyory 2015). The heterogeneity of macrophages is also observed in the mononuclear phagocyte system. The macrophages develop from the haematopetic stem cells that are multi-potent in nature and are self-renewing (Locati and Sica 2012). Different cell types MPI cells are non transformed, self renewing, primary phagocytes which are GM-CSF dependent. They are portrayed as murine model of Alveolar Macrophages due to similar properties (Fejer et al. 2015). The MPI cell model system contains cell population that are multiclonal and heterogeneous (size, function and morphology) in nature. On the contrary in AMs, this framework gives unhindered measures of essential macrophages, appropriate for intensive biochemical examination (Locati and Sica 2012). MPI cells are different from bone marrow derived macrophages and dendrite cells. The latter two are widely used in macrophage studies. However, MPI cells produces more amount of TNF- and IL-6 upon stimulation with the TLR4-dependent LPS (Epelman et al. 2014). Hypothesis This research is conducted to characterize individual cell clones of MPI functionally, and to prepare a pure culture of these clones in order to potentially reduce heterogeneity which derives from polyclonality. Proper optimization of attachment to the substrate, composition of the basal media, source of serum and the addition of the factors, which promote the proliferation of the cell, is the key to successful cloning. Additionally this research also intends to examine the reactions of these cloned cells towards various pathogens, ligands derived from pathogens and cytokines. This can be brought about by diverse tissue culture techniques such as cloning of single cell, analysis of growth curve and ELISA. The conducted research hypothesizes that obtaining pure culture of macrophages is possible from polyclonal MPI cell line. Appendix The figure below illustrates the self-renewal of Embryonic macrophages in homeostatic conditions, from foetal liver and the yolk sac. They are driven by M-CSF or GM-CSF. Self-renewing is also possible in inflammatory macrophages of embryonic origin. (Source: Fejer et al. 2015) References Davies, L.C., Jenkins, S.J., Allen, J.E. and Taylor, P.R., 2013. Tissue-resident macrophages.Nature immunology,14(10), pp.986-995. Epelman, S., Lavine, K.J. and Randolph, G.J., 2014. Origin and functions of tissue macrophages.Immunity,41(1), pp.21-35. Fejer, G., Sharma, S. and Gyory, I., 2015. Self-renewing macrophagesA new line of enquiries in mononuclear phagocytes.Immunobiology,220(2), pp.169-174. Fejer, G., Wegner, M.D., Gyry, I., Cohen, I., Engelhard, P., Voronov, E., Manke, T., Ruzsics, Z., Dlken, L., da Costa, O.P. and Branzk, N., 2013. Nontransformed, GM-CSFdependent macrophage lines are a unique model to study tissue macrophage functions.Proceedings of the National Academy of Sciences,110(24), pp.E2191-E2198. Locati, M., Mantovani, A. and Sica, A., 2012. Macrophage activation and polarization as an adaptive component of innate immunity.Advances in immunology,120, pp.163-184. Yona, S., Kim, K.W., Wolf, Y., Mildner, A., Varol, D., Breker, M., Strauss-Ayali, D., Viukov, S., Guilliams, M., Misharin, A. and Hume, D.A., 2013. Fate mapping reveals origins and dynamics of monocytes and tissue macrophages under homeostasis.Immunity,38(1), pp.79-91.