Eosinophil Activation by Toll-Like Receptor 4 Ligands Regulates Macrophage Polarization

Abstract

Eosinophils are terminally differentiated granulocytes that have long been considered as destructive cells associated with Th2 type immune responses such as allergic inflammation and helminth infections. Recently, eosinophils have been actively studied as multifunctional leukocytes regulating an array of physiological responses through interaction with other immune cells. In this study, we examined the expression and function of Toll-like receptors (TLRs) in eosinophilic EoL-1 cells and demonstrated the expression of a number of immune mediators in activated EoL-1 cells and their interaction with the macrophage cell line THP-1 upon TLR4 ligand stimulation. EoL-1 cells differentiated with butyrate increased expression of TLR3, TLR4, and TLR7 at mRNA and protein level with flow cytometry analysis. Mature eosinophils derived from human cord blood CD34 + cells were subjected to RNA-sequencing, and showed the expression of a panel of TLR transcripts and TLR4 was the most highly expressed TLR. Among the cognate ligands of TLR3, TLR4, and TLR7, lipopolysaccharide (LPS) or palmitic acid significantly increased mRNA expression of immune mediators in differentiated EoL-1 cells. Notably, Western blot analysis of palmitic acid-treated differentiated EoL-1 cells showed significantly up-regulated expression of Th2 type cytokines and transcription factors driving eosinophil differentiation. To evaluate functional significance of TLR4 ligand-stimulated eosinophils, we added conditioned media (CM) from EoL-1 cells to differentiated THP-1 cells and assessed the expression of M1 macrophage or M2 macrophage-related markers. M1 and M2 macrophage markers were significantly upregulated by CM from LPS and palmitic acid stimulated EoL-1 cells, respectively. In addition, the adipose tissue of obese mice, where eosinophils are decreased due to obesity-induced inflammation, showed significantly decreased frequency of M2 macrophages, despite an increase in the total macrophage numbers. Based on these collective data, we proposed that eosinophils regulate both inflammatory and anti-inflammatory polarization of macrophages through functional changes induced by different TLR4 ligands.

The anti‐parasitic drug miltefosine suppresses activation of human eosinophils and ameliorates allergic inflammation in mice

“…Importantly, miltefosine decreased toll‐like receptor 4 (TLR‐4) recruitment to the cell surface of macrophages and dampened IL‐1β release following stimulation with lipopolysaccaride (LPS) (Iacano et al, 2019). Given the fact that TLR‐4 stimulation on eosinophils can help polarize macrophages towards pro‐ or anti‐inflammatory phenotypes (Yoon et al, 2019), this finding further supports the evidence that miltefosine may influence the interplay and balance between various immune cell types during the state of inflammation.…”

Disrupting Bordetella Immunosuppression Reveals a Role for Eosinophils in Coordinating the Adaptive Immune Response in the Respiratory Tract

“…The defects of EO - mice in cytokine production, lymphocytes recruitment, and lymphocyte organization into aggregates suggest eosinophils may be important in the efficient generation of local lymphoid structures in which lymphocytes are activated and develop. Eosinophils possess Toll-Like Receptors [ 85 , 86 , 87 , 88 , 89 ], indicating that they harbor receptors to respond to infections and trigger the required immune response. This response could be relatively direct; for example, eosinophils might directly present antigens to T cells, as they do during parasitic [ 24 , 25 , 90 ], viral [ 48 ], and allergic reactions [ 91 ], indicating they have the required machinery to respond to bacterial infections and activate the subsequent inflammatory response and augment the following adaptive responses.…”

Adipose Tissue Immunomodulation: A Novel Therapeutic Approach in Cardiovascular and Metabolic Diseases

“…AT-resident eosinophils are sustained by AT multipotent stromal cells-derived CCL11 and ILC2-derived IL-5 ( 207 , 208 ). Indeed, AT-resident eosinophils produce IL-4 and IL-13 that drive macrophage M2 polarization, trigger Th2 differentiation, enhance B cell activation and promote metabolic homeostasis ( 209 , 210 ). Eosinophil-deficient HFD-fed mice showed pronounced IR ( 209 , 211 ).…”