RNA-seq evaluation of equine alveolar macrophages and monocyte-derived macrophages exposed to an inflammatory stimulus (short communication).
Abstract: Macrophage populations in the lung, including resident alveolar macrophages (AMs) and recruited monocyte-derived macrophages (MDMs), recognize the inhaled particulates in barn dust that cause severe equine asthma and orchestrate an immune response though the cytokines they produce. Despite their importance, the specific contributions of these macrophage subsets to lower airway inflammation remain poorly understood. This exploratory in vitro study investigated the likely contributions of AMs and MDMs from healthy horses to the early inflammatory response using RNA-seq. If biologically important contrasts were identified, future studies to elucidate differences in AM and MDM function in severely asthmatic horses could be undertaken. AMs and MDMs from six healthy female Standardbred horses were exposed for 6 h to a mixture of ungal spores, ipopolysaccharide, and ilica microspheres (FLS), which represents the major components of barn dust, with serum-free cell culture medium as the control. Equine AMs and MDMs exposed to FLS showed broadly similar transcriptional responses, with cytokine signalling emerging as the dominant biological theme in both cell types. At an exploratory FDR threshold of 0.25, gene set enrichment analysis indicated that “JAK-STAT/IL-15 signalling pathway”, “NOD-like receptor signalling pathway”, and “infection/C-type lectin receptor” had greater enrichment in FLS-exposed MDMs than AMs. These exploratory data indicate that equine AMs and MDMs mount largely overlapping cytokine responses to the elements that contribute to exacerbation of severe equine asthma, but also exhibit cell-type specific pathway differences. This work establishes the baseline for future studies testing the hypothesis that in horses with severe equine asthma, AMs and MDMs each have altered function that contribute uniquely to disease pathogenesis. The online version contains supplementary material available at 10.1186/s12917-026-05322-0.
Publication Date: 2026-02-06 PubMed ID: 41652496PubMed Central: PMC12977879DOI: 10.1186/s12917-026-05322-0Google Scholar: Lookup
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- Journal Article
Summary
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Overview
- This study investigates how two types of immune cells in horse lungs—alveolar macrophages (AMs) and monocyte-derived macrophages (MDMs)—respond at the gene expression level when exposed to components of barn dust, which triggers severe equine asthma.
- The research uses RNA sequencing (RNA-seq) to explore similarities and differences in their early inflammatory responses, establishing a baseline for future studies on asthmatic horses.
Background
- Macrophages are important immune cells in the lungs, responsible for recognizing inhaled harmful particles like those found in barn dust.
- There are two main macrophage populations in the lungs:
- Alveolar macrophages (AMs): Resident immune cells that naturally reside in the lung alveoli.
- Monocyte-derived macrophages (MDMs): Recruited from circulating blood monocytes during inflammation.
- Exposure to barn dust particulates leads to severe equine asthma, a respiratory disease characterized by airway inflammation.
- The cytokines produced by AMs and MDMs orchestrate the immune response to these inhaled particles.
- The distinct roles of AMs versus MDMs in airway inflammation and asthma pathogenesis in horses are not well understood.
Objectives
- To characterize and compare the early inflammatory gene expression responses of AMs and MDMs from healthy horses exposed to a mixture mimicking barn dust components.
- To identify cell-type specific pathways that could be involved in the progression of severe equine asthma.
- To provide a foundation for future research focusing on horses with severe equine asthma.
Methods
- Samples were taken from six healthy female Standardbred horses.
- Isolation of lung macrophages:
- Resident alveolar macrophages (AMs)
- Monocyte-derived macrophages (MDMs)
- Exposure conditions:
- Cells were exposed for 6 hours to a mixture called FLS, containing:
- Ungal spores
- Lipopolysaccharide (LPS), a bacterial component
- Silica microspheres
- FLS mixture simulates major components of barn dust relevant to asthma exacerbation.
- Control condition used serum-free cell culture medium without FLS.
- Cells were exposed for 6 hours to a mixture called FLS, containing:
- RNA sequencing (RNA-seq) was performed to analyze gene expression profiles after exposure.
- Data analyzed under exploratory conditions with a threshold false discovery rate (FDR) of 0.25 to identify differentially expressed genes and enriched pathways.
Key Findings
- Both AMs and MDMs showed broadly similar transcriptional responses upon FLS exposure.
- The dominant biological theme in both cell types involved cytokine signaling, indicating activation of immune response pathways.
- Gene set enrichment analysis revealed:
- Greater enrichment in MDMs for pathways such as:
- JAK-STAT/IL-15 signaling pathway
- NOD-like receptor signaling pathway
- Infection and C-type lectin receptor signaling pathways
- This suggests some unique functional differences between MDMs and AMs in response to the inflammatory stimulus.
- Greater enrichment in MDMs for pathways such as:
Conclusions and Implications
- This exploratory study establishes that AMs and MDMs in healthy horses react largely equivalently to the inflammatory trigger mimicking barn dust exposure, mainly through cytokine-mediated pathways.
- Differences in pathway enrichment suggest that each macrophage type may contribute uniquely to inflammation and immune regulation.
- The findings provide a baseline for future, more detailed investigations into how these two macrophage types behave in horses with severe equine asthma.
- Understanding these differences could help clarify disease mechanisms and potentially guide targeted therapies for managing severe equine asthma.
Additional Notes
- The study is designated as a short communication, indicating it presents preliminary or concise data.
- Supplementary materials related to the study are available online, offering expanded details and supporting data.
Cite This Article
APA
Kang H, Lee GKC, Bienzle D, Hammermüller J, Arroyo LG, Lillie BN, Beeler-Marfisi J.
(2026).
RNA-seq evaluation of equine alveolar macrophages and monocyte-derived macrophages exposed to an inflammatory stimulus (short communication).
BMC Vet Res, 22(1), 161.
https://doi.org/10.1186/s12917-026-05322-0 Publication
Researcher Affiliations
- Department of Pathobiology, University of Guelph, Guelph, ON, Canada.
- Sanofi Canada, North York, ON, Canada.
- Department of Pathobiology, University of Guelph, Guelph, ON, Canada.
- IDEXX Laboratories Pty. Ltd, Rydalmere, NSW, Australia.
- Department of Pathobiology, University of Guelph, Guelph, ON, Canada.
- Department of Pathobiology, University of Guelph, Guelph, ON, Canada.
- Department of Clinical Studies, University of Guelph, Guelph, ON, Canada.
- Department of Pathobiology, University of Guelph, Guelph, ON, Canada.
- Department of Pathobiology, University of Guelph, Guelph, ON, Canada. jbeelerm@uoguelph.ca.
Grant Funding
- EG 2017 01 / Equine Guelph
- 27364 / Ontario Ministry of Agriculture, Food and Agribusiness
Conflict of Interest Statement
Declarations. Ethics approval and consent to participate: The project was approved under Animal Use Protocols 3816 and 4675 by the University of Guelph’s Animal Care Committee. Consent for publication: Not applicable. Horses were from the University of Guelph equine research herd. Competing interests: The authors declare no competing interests.
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