Abstract
BackgroundResident macrophages (Mø) originating from yolk sac Mø and/or foetal monocytes colonise tissues/organs during embryonic development. They persist into adulthood by self-renewal at a steady state, independent of adult monocyte inputs, except for those in the intestines and dermis. Thus, many resident Mø can be propagated in vitro under optimal conditions; however, there are no specific in vitro culture methods available for the propagation of resident Mø from diverse tissues/organs.ResultsWe provided a simple method for propagating resident Mø derived from the liver, spleen, lung, and brain of ICR male mice by co-culture and subculture along with the propagation of other stromal cells of the respective organs in standard culture media and successfully demonstrated the propagation of resident Mø colonising these organs. We also proposed a simple method for segregating Mø from stromal cells according to their adhesive property on bacteriological Petri dishes, which enabled the collection of more than 97.6% of the resident Mø from each organ. Expression analyses of conventional Mø markers by flow cytometry showed similar expression patterns among the Mø collected from the organs.ConclusionThis is the first study to clearly provide a practical Mø propagation method applicable to resident Mø of diverse tissues and organs. Thus, this novel practical Mø propagation method can offer broad applications for the use of resident Mø of diverse tissues and organs.
Highlights
Resident macrophages (Mø) originating from yolk sac Mø and/or foetal monocytes colonise tissues/ organs during embryonic development
Mø are largely divided into two types: (1) resident Mø, which colonise tissues/organs at a steady state and perform tissue/organ-specific functions to maintain tissue homeostasis, and (2) recruited Mø or bone-marrow derived Mø, which differentiate from circulating monocytes in the blood infiltrating lesions in response to damage of tissues/organs
Ogawa et al BMC Immunology (2019) 20:34 resident Mø in the steady state have been identified, including colony stimulating factor 1 (CSF-1) for Kupffer cells, red pulp Mø, and other resident Mø; colony stimulating factor 2 (CSF-2) for alveolar Mø; and interleukin (IL)-34 for microglia [1, 5,6,7]. These findings suggest that most resident Mø have the capacity to proliferate in vitro under suitable conditions, which opens up the possibility of obtaining a large number of resident Mø for a variety of research applications, including those currently utilising adult monocyte-derived Mø
Summary
Resident macrophages (Mø) originating from yolk sac Mø and/or foetal monocytes colonise tissues/ organs during embryonic development. Ogawa et al BMC Immunology (2019) 20:34 resident Mø in the steady state have been identified, including colony stimulating factor 1 (CSF-1) for Kupffer cells, red pulp Mø, and other resident Mø; colony stimulating factor 2 (CSF-2) for alveolar Mø; and interleukin (IL)-34 for microglia [1, 5,6,7]. These findings suggest that most resident Mø have the capacity to proliferate in vitro under suitable conditions, which opens up the possibility of obtaining a large number of resident Mø for a variety of research applications, including those currently utilising adult monocyte-derived Mø. An improved in vitro method is needed to advance research on the specific behaviours of resident Mø in diverse tissues/organs in response to various cytokines and molecules produced by pathogens such as lipopolysaccharide (LPS)
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