Effect of aging on monocyte phagocytic and inflammatory functions, and on the ex vivo inflammatory responses to lipopolysaccharide, in horses.
Abstract: Studies investigating age-related changes in the function of monocytes are currently limited for horses. Thus, the main goal of this study was to determine the effect of aging on monocyte phagocytic capacity and pro-inflammatory cytokine responses to bacterial lipopolysaccharide (LPS). A second goal of this work was to examine the effect of aging on the inflammatory cytokine responses to LPS in a whole blood ex vivo model. Seven healthy young adult (4-6 years of age) and seven healthy senior horses (>20 years of age) were enrolled. Phagocytosis of E. coli, and pro-inflammatory cytokine (TNFα) responses to LPS, were measured in monocytes by flow cytometry. Gene expressions of pro-inflammatory cytokines (TNFα, IL-1β, IL-6, IL-8, IL-18, CCL-5, CCL-2) were measured in peripheral blood mononuclear cells (PBMCs) and whole blood by RT-qPCR post incubation for 2 h or 6 h with a low (0.01 µg/mL) or a high (1 µg/mL) dose of LPS. Two sets of statistical models were applied to compare the age groups, one adjusted, and one unadjusted for the horses' body condition scores (BCS). The percentage of monocytes that phagocytosed E. coli after 2 h of incubation was significantly lower in senior compared to young adult horses in the BCS-adjusted model. In the senior group, the expression of IL-1β in 2 h-0.01 µg/mL LPS-stimulated PBMCs was significantly higher than in the young adult group (BCS-adjusted and unadjusted models). In senior horses, expressions of IL-8 and IL-6 in whole blood samples stimulated for 6 h with 0.01 µg/mL LPS and for 2 h with 1 µg/mL LPS, respectively, were significantly lower than in young adult horses (BCS-adjusted models). The results of this study suggest that the phagocytic function of monocytes, as well as their IL-1β response to LPS may be altered in senior horses. In addition, the whole blood IL-8 and IL-6 gene expression responses to LPS may be insufficient in senior horses. While investigation of the effect of BCS on monocyte functions and whole blood pro-inflammatory LPS-responses was not a major goal of this work, it appears that adiposity may play a role in innate immune cell function, as significant differences between the age groups were often not apparent until the models were adjusted for BCS.
Copyright © 2022 Elsevier B.V. All rights reserved.
Publication Date: 2022-07-12 PubMed ID: 35863208DOI: 10.1016/j.vetimm.2022.110459Google Scholar: Lookup
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Summary
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The research investigates how aging impacts the functionality of immune cells in horses, specifically focusing on the ability of aged monocytes to engulf bacteria and respond to bacteria-derived lipopolysaccharide. The study also examines how age affects the blood’s overall inflammatory response to lipopolysaccharide.
Study Objective and Design
- The primary aim of the research was to study the effects of aging on horse monocyte immune functions. Such studies are currently scarce.
- Two specific aspects of monocyte functionality were investigated: their ability to engulf the bacteria E. coli (known as phagocytosis), and their responses to lipopolysaccharide (a cell surface component of some bacteria) in terms of producing pro-inflammatory cytokines, which are chemical messengers of the immune system.
- A secondary aim was to compare the systemic inflammatory response of the blood to lipopolysaccharide in a laboratory setting (ex vivo) between young and old horses.
- The study enrolled seven healthy adult horses (aged between 4-6 years) and seven senior horses (over 20 years old).
Methodology
- Cytokine response to lipopolysaccharide and phagocytic capacity were measured in isolated monocytes using flow cytometry, a method to analyze physical and chemical features of cells.
- Gene expression for various pro-inflammatory cytokines was measured after exposure to varying doses of lipopolysaccharide for different durations. The different cytokines assessed included tumor necrosis factor alpha (TNFα), various interleukins (IL-1β, IL-6, IL-8, IL-18), and specific chemokines (CCL-5, CCL-2).
- Two sets of statistical models were employed – one adjusted for body condition scores (an indicator of the horses’ overall adiposity or body fat levels), and one unadjusted.
Results and Conclusions
- Phagocytic capacity and inflammatory reactivity of monocytes were affected by age. A lower number of monocytes in the senior group were able to engulf E. coli, whereas they responded more strongly to lipopolysaccharide in terms of interleukin-1β production.
- In the senior group, responses to lipopolysaccharide in the form of interleukin-8 and interleukin-6 production were lower than in the young group, suggesting potential impairment in their systemic inflammatory responses.
- The investigators observed body condition scores affected the results. The difference between young and old horses was sometimes only apparent when adjusting for variations in body condition scores – indicating body fat levels may influence immune functions.
- These findings shed light on age-related changes in the immune response of horses, particularly for innate immune cells. This may have potential implications for how senior horses respond to bacterial infections and inflammation.
Cite This Article
APA
Herbst AC, Reedy SE, Page AE, Horohov DW, Adams AA.
(2022).
Effect of aging on monocyte phagocytic and inflammatory functions, and on the ex vivo inflammatory responses to lipopolysaccharide, in horses.
Vet Immunol Immunopathol, 250, 110459.
https://doi.org/10.1016/j.vetimm.2022.110459 Publication
Researcher Affiliations
- M. H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA. Electronic address: alisa.herbst@gmx.net.
- M. H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA.
- M. H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA.
- M. H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA.
- MARS EQUESTRIAN™ Research Fellow, M. H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA.
MeSH Terms
- Aging
- Animals
- Cytokines
- Escherichia coli
- Horses
- Interleukin-6 / metabolism
- Interleukin-8 / genetics
- Leukocytes, Mononuclear / metabolism
- Lipopolysaccharides / pharmacology
- Monocytes
- Tumor Necrosis Factor-alpha / genetics
Citations
This article has been cited 2 times.- DeNotta S, McFarlane D. Immunosenescence and inflammaging in the aged horse. Immun Ageing 2023 Jan 6;20(1):2.
- Asahi Y, Arai T, Tanaka Y. Changes in plasma metabolite concentrations and enzyme activities in aging riding horses. Front Vet Sci 2024;11:1345548.
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