Abstract
Macrophages play an indispensable role in both innate and acquired immunity, while the persistence of activated macrophages can sometimes be harmful to the host, resulting in multi-organ damage. Macrophages develop from monocytes in the circulation. However, little is known about the organ affinity of macrophages in the normal state. Using in vivo imaging with XenoLight DiR®, we observed that macrophages showed strong affinity for the liver, spleen and lung, and weak affinity for the gut and bone marrow, but little or no affinity for the kidney and skin. We also found that administered macrophages were still alive 168 hours after injection. On the other hand, treatment with clodronate liposomes, which are readily taken up by macrophages via phagocytosis, strongly reduced the number of macrophages in the liver, spleen and lung.
Highlights
Macrophages are a type of myeloid cell that play an indispensable role in both innate and acquired immunity [1]
Quantitative analysis showed that the difference between the intensity of fluorescence signal from mice which received 5×106 labeled macrophages and that from mice with 2×106 labeled macrophages was clearly distinguishable (Fig 1B), suggesting that fluorescence intensity paralleled the number of macrophages
Total fluorescence signal from macrophages decreased only by 29.3% 168 hours after administration (Fig 1A), suggesting that labeled macrophages were still viable in vivo and the fluorescence of XenoLight DiR1 did not fade for a long period
Summary
Macrophages are a type of myeloid cell that play an indispensable role in both innate and acquired immunity [1]. Macrophage phenotypes and functions can vary with different external stimuli, and macrophages are divided into two major classifications: classically activated, i.e. inflammatory, and alternatively activated, i.e. anti-inflammatory macrophages [1]. Persistence of activated macrophages can sometimes be harmful to the host [2, 3].
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