Resident macrophages restrain pathological adipose tissue remodeling and protect vascular integrity in obese mice.

Tissue-resident macrophages in white adipose tissue (WAT) dynamically adapt to the metabolic changes of their microenvironment that are often induced by excess energy intake. Currently, the exact contribution of these macrophages in obesity-driven WAT remodeling remains controversial. Here, using a transgenic CD169-DTR mouse strain, we provide new insights into the interplay between CD169+ adipose tissue macrophages (ATMs) and their surrounding WAT microenvironment. Using targeted in vivo ATM ablation followed by transcriptional and metabolic WAT profiling, we found that ATMs protect WAT from the excessive pathological remodeling that occurs during obesity. As obesity progresses, ATMs control not only vascular integrity, adipocyte function, and lipid and metabolic derangements but also extracellular matrix accumulation and resultant fibrosis in the WAT. The protective role of ATMs during obesity-driven WAT dysfunction supports the notion that ATMs represent friends, rather than foes, as has previously assumed.

Organ-Specific Fate, Recruitment, and Refilling Dynamics of Tissue-Resident Macrophages during Blood-Stage Malaria.

Inflammation-induced disappearance of tissue-resident macrophages represents a key pathogen defense mechanism. Using a model of systemic blood-stage malaria, we studied the dynamics of tissue-resident macrophages in multiple organs to determine how they are depleted and refilled during the course of disease. We show that Plasmodium infection results in a transient loss of embryonically established resident macrophages prior to the parasitemia peak. Fate-mapping analysis reveals that inflammatory monocytes contribute to the repopulation of the emptied niches of splenic red pulp macrophages and hepatic Kupffer cells, while lung alveolar macrophages refill their niche predominantly through self-renewal. Interestingly, the local microenvironment of the spleen and liver can "imprint" the molecular characteristics of fetal-derived macrophages on newly differentiated bone marrow-derived immigrants with remarkably similar gene expression profiles and turnover kinetics. Thus, the mononuclear phagocytic system has developed distinct but effective tissue-specific strategies to replenish emptied niches to guarantee the functional integrity of the system.

Tissue-Resident CD169(+) Macrophages Form a Crucial Front Line against Plasmodium Infection.

Tissue macrophages exhibit diverse functions, ranging from the maintenance of tissue homeostasis, including clearance of senescent erythrocytes and cell debris, to modulation of inflammation and immunity. Their contribution to the control of blood-stage malaria remains unclear. Here, we show that in the absence of tissue-resident CD169(+) macrophages, Plasmodium berghei ANKA (PbA) infection results in significantly increased parasite sequestration, leading to vascular occlusion and leakage and augmented tissue deposition of the malarial pigment hemozoin. This leads to widespread tissue damage culminating in multiple organ inflammation. Thus, the capacity of CD169(+) macrophages to contain the parasite burden and its sequestration into different tissues and to limit infection-induced inflammation is crucial to mitigating Plasmodium infection and pathogenesis.