Eosinophil‐derived IL ‐4 is necessary to establish the inflammatory structure in innate inflammation

Abstract

Pathogen‐induced inflammation comprises pro‐ and anti‐inflammatory processes, which ensure pathogen removal and containment of the proinflammatory activities. Here, we aimed to identify the development of inflammatory microenvironments and their maintenance throughout the course of a toll‐like receptor 2‐mediated paw inflammation. Within 24 h after pathogen‐injection, the immune cells were organized in three zones, which comprised a pathogen‐containing “core‐region”, a bordering proinflammatory (PI)‐region and an outer anti‐inflammatory (AI)‐region. Eosinophils were present in all three inflammatory regions and adapted their cytokine profile according to their localization. Eosinophil depletion reduced IL‐4 levels and increased edema formation as well as mechanical and thermal hypersensitivities during resolution of inflammation. Also, in the absence of eosinophils PI‐ and AI‐regions could not be determined anymore, neutrophil numbers increased, and efferocytosis as well as M2‐macrophage polarization were reduced. IL‐4 administration restored in eosinophil‐depleted mice PI‐ and AI‐regions, normalized neutrophil numbers, efferocytosis, M2‐macrophage polarization as well as resolution of zymosan‐induced hypersensitivity. In conclusion, IL‐4‐expressing eosinophils support the resolution of inflammation by enabling the development of an anti‐inflammatory framework, which encloses proinflammatory regions.

Meloxicam treatment disrupts the regional structure of innate inflammation sites by targeting the pro‐inflammatory effects of prostanoids

“…The post-bleaching images were subtracted from the subsequent fluorescence image. The antibodies used for the MELC procedure are listed in Table S1 and have been validated previously (Kolbinger et al, 2022(Kolbinger et al, , 2023Kornstädt et al, 2020;Pierre et al, 2017;Pierre & Scholich, 2010). Stainings without secondary antibodies served as negative controls for COX-1 and COX-2 antibodies.…”

“…To determine whether the observed quantitative changes indicated broader alterations in the immune cell network, we analysed the likelihood of finding different cell types adjacent to each other compared to randomized versions of the same tissue (Figure S4) (Schapiro et al, 2017). Given that M1-like and M2-like macrophages are key cells types that determine the regional structure during zymosan-induced inflammation (Kolbinger et al, 2023), we initially focused on cell clusters defined by combinations of markers characterizing clusters as M1-like macrophages (Siglec F À /F4-80 + /CD86 + / CD206 À ), M2-like macrophages (Siglec F À /F4-80 + /CD86 À /CD206 + ) and non-polarized M0 macrophages (Siglec F À /F4-80 + /CD86 + / CD206 + ). Linear distance maps of the relative distance between zymosan and these cell clusters in control mice revealed that M1-like macrophages accumulated in the direct neighbourhood of zymosan whereas M2-like macrophages were excluded from this area (Figure 3a).…”

“…Zymosan has a particulate structure and is immobilized at the site of injection, allowing the localization of labelled particles. This provides insight into the structure of an inflamed region in relation to the pathogen (Kern et al, 2018; Kolbinger et al, 2023; Pierre et al, 2017). The structure comprised a pathogen‐containing core region, an adjacent PI region defined by M1‐like macrophages and a surrounding AI region defined by M2‐like macrophages (Kolbinger et al, 2023).…”

“…This provides insight into the structure of an inflamed region in relation to the pathogen (Kern et al, 2018; Kolbinger et al, 2023; Pierre et al, 2017). The structure comprised a pathogen‐containing core region, an adjacent PI region defined by M1‐like macrophages and a surrounding AI region defined by M2‐like macrophages (Kolbinger et al, 2023). Importantly, this regional structure mirrored the effects of specific PI or AI interventions such as eosinophil depletion or the administration of interleukin (IL)‐4.…”

“…We characterized the structural alterations to determine whether the delayed resolution of inflammation by NSAIDs is based on losing the AI effects of prostanoids or interference with PI processes such as pathogen clearance. The analysis of 45 immune cell markers using established bioinformatic approaches (Kolbinger et al, 2022, 2023; Kornstädt et al, 2020; Schapiro et al, 2017) highlighted the regional structure associated with TLR2‐mediated inflammation and identified the underlying changes in immune cell localization, recruitment and activation.…”