Human monocyte‐derived macrophages spontaneously differentiated in vitro show distinct phenotypes

Abstract

Tissue macrophages are resident phagocytes that acquire specific phenotypes according to the microenvironment. Morphological and functional heterogeneity has been evidenced in different homeostatic and pathological conditions. Indeed, the nature of macrophage subsets may have either harmful or beneficial functions in disease progression/resolution. Therefore the possibility to pharmacologically manipulate heterogeneity represents a relevant challenge. Since human tissue macrophages are not easily obtained, various in vitro models are currently used that do not adequately reflect the heterogeneity and plasticity of tissue macrophages. We had previously reported that two dominant and distinct macrophage morphotypes co-exist in the same culture of human monocytes spontaneously differentiated for 7 days in autologous serum. The present study was aimed to the phenotypic characterization of these morphotypes, that is, round- and spindle-shaped. We observed that, besides substantial differences in cytoskeleton architecture, round monocyte-derived macrophages (MDMs) showed higher lipid content, increased macropinocytosis/efferocytosis capacity, and overexpression of CD163, interleukin (IL)-10, and transforming growth factor (TGF) β2. Conversely, spindle MDMs exhibited enhanced respiratory burst and higher expression of the chemokine (C-C motif) ligands 18 and 24 (CCL18 and CCL24). Overall, round MDMs show functional traits reminiscent of the non-inflammatory and reparative M2 phenotype, whereas spindle MDMs exhibit a pro-inflammatory profile and express genes driving lymphocyte activation and eosinophil recruitment. MDMs obtained in the culture condition herein described represent a valuable model to disentangle and manipulate the functional heterogeneity of tissue macrophages that has been disclosed in scenarios spanning from inflammatory and wounding responses to atherosclerotic lesions.

Isolation of Mouse and Human Tumor-Associated Macrophages

“…It is important that the phenotype and the transcriptome of macrophages extracted from human tissues are compared with matched controls, ideally from the same tissue type; in vitro monocyte-derived macrophages, frequently used as normal negative controls, are an heterogeneous population of macrophages with different phenotypes and functions [45] and do not represent optimal controls for these kind of studies.…”

Intracellular growth of Mycobacterium avium subspecies and global transcriptional responses in human macrophages after infection

“…Tissue resident macrophages represent a heterogeneous population and it is not clear whether M. avium infect a particular phenotype. Monocyte derived macrophages matured in absence of any stimuli give rise to a mixed culture of both the M1 and M2 phenotype [10] and such cultures may thus be considered appropriate for infection studies with M. avium . Finally, using macrophages derived from the relevant target species is important since the global inflammatory response evoked in mice recently was demonstrated to be vastly different from humans [11].…”

The Human Tissue–Biomaterial Interface: A Role for PPARγ-Dependent Glucocorticoid Receptor Activation in Regulating the CD163+M2 Macrophage Phenotype

“…We are unaware of any other study that documents this in vitro CD163 + subpopulation, although Philippidis et al documented increased CD163 expression by human-monocyte-derived macrophages in culture 28 and Eligini et al recently described the spontaneous differentiation of distinct macrophage phenotypes in vitro where CD163 expression was greater in monocyte-derived macrophages with a rounded, rather than spindle, morphology. 29 Porta et al described a population of macrophages that are ''tolerant'' in response to endotoxin and display an inherent skewing toward the M2 phenotype with impaired M1 responses. 30 It is intriguing to postulate that the CD163 + population maintained in culture represents monocytederived macrophages with a greater propensity toward antiinflammatory/M2 macrophage function.…”