# Metabolic phenotype of bovine blood-derived neutrophils is altered in milk

## TL;DR

Bovine neutrophils in milk show altered metabolism and function depending on whether the udder is healthy or inflamed.

## Contribution

The study reveals distinct metabolic and functional differences between blood- and milk-derived neutrophils in healthy and inflamed udders.

## Key findings

- Milk-derived neutrophils show divergent expression of MHC class II and CD25 compared to blood-derived neutrophils.
- Reactive oxygen species production and apoptosis differ between neutrophils from healthy and inflamed udders.
- Metabolic phenotype changes in milk neutrophils correlate with the health status of mammary gland quarters.

## Abstract

In a healthy udder, immune cells from the peripheral bloodstream migrate into mammary tissue in low numbers to provide baseline immune surveillance, without triggering inflammation. In bovine intramammary inflammation, on the other hand, high amounts of leukocytes are recruited, causing severe inflammation. We were interested in leukocyte subpopulations and functional differences between blood- and milk-derived neutrophils from healthy and inflamed udder quarters. In this context, we found a distinct leukocyte subpopulation profile dependent on the health status of mammary gland quarters, with a predominant T cells population in heathy mammary gland quarters and a shift to macrophages and granulocytes in inflammation. Further, we detected divergent expression of major histocompatibility complex class II and interleukin 2 receptor CD25 on the surface of milk- and blood-derived neutrophils, pointing to antigen presentation and immune modulatory properties. Moreover, we observed differences in production of reactive oxygen species, deviant early and late apoptosis and functional changes in these cells, pointing to an altered metabolic phenotype in milk cells dependent on the health status of mammary gland quarters. These findings provide insights into the functional adaptations of neutrophils in different environments, highlighting the importance of metabolic alterations for immune cell function.