Non-classical monocytes contribute to innate immune training in cattle

Area of Science:

• Immunology
• Cell Biology
• Veterinary Science

Background:

• Innate immune training enhances immune cell responses to secondary pathogen encounters.
• Beta-glucans (βG), derived from Saccharomyces cerevisiae cell walls, are known inducers of trained immunity.
• Understanding trained immunity in bovine monocytes is crucial for animal health.

Purpose of the Study:

• To investigate if βG induces innate immune training in bovine monocytes in vitro.
• To determine the role of different monocyte subpopulations in βG-induced trained immunity.
• To explore conditions influencing monocyte training, such as M1 polarization.

Main Methods:

• Bovine monocytes were isolated and stimulated with βG.
• Trained immunity was assessed by measuring TNF secretion after secondary stimulation with Escherichia coli LPS.
• Monocytes were sorted into classical, intermediate, and non-classical subpopulations for individual and mixed population analysis.

Main Results:

• Isolated classical and intermediate monocytes, or single populations of all three subsets, could not be trained by βG.
• Macrophages derived from plastic-adherent mononuclear cells showed trained function.
• βG successfully induced trained immunity in mixed monocyte populations containing all three subsets, particularly non-classical monocytes.
• Training efficacy was linked to conditions promoting M1 macrophage polarization.

Conclusions:

• Innate immune training in bovine monocytes is dependent on the presence of non-classical monocytes within a mixed population.
• This finding highlights a specific role for non-classical monocytes in mediating trained immunity in cattle.
• The study provides new insights into the mechanisms of trained immunity in the bovine immune system.