In many animal species, anti-inflammatory immune cells are normal residents of lean adipose depots and produce a barrier of related cytokines that protect against metabolic syndrome. Our objective was to determine if similar immune cells reside in mid-jejunum mesenteric adipose tissue (MAT) of randomly selected lean Holstein Friesian cows from an abattoir. Body condition scores were determined before slaughter (mean BCS = 2.74). Stromal cell fractions (SCF) were prepared from washed, minced MAT digested with type I collagenase. Following digestion and cleaning of the sample, cells were stained with bovine immune cell marker specific monoclonal antibodies expressed on macrophages, dendritic cells, T lymphocytes and T regulatory lymphocytes (T regs). Background controls consisted of cells stained with irrelevant, isotype-matched control antibodies. SCF composition was analyzed across 10,000 cells/sample using a Becton Dickson FACS Calibur Flow Cytometer. Marker specific fluorescence was compared with background fluorescence in controls by ANOVA. Marker expression is summarized in the table below. Results from this work indicate that populations of innate (macrophage and dendritic cells) and adaptive (lymphocytes and T regs) immune response cells do in fact reside in MAT of lean cows (Table 1). Furthermore, expression of MHC class II in the context of dendritic cells or macrophages and T lymphocytes suggests adaptive immune responses do occur in MAT. Subpopulations of FoxP3⁺ regulatory T lymphocytes were the dominant effector lymphocyte, implying that anti-inflammatory functions could contribute to MAT homeostasis in lean cows and potentially protect against development of metabolic disease. Table 1. Presence of immune cells mesenteric adipose tissue (MAT) of Holstein Friesian cows

Presumptive cell type		Marker	Percent of SCF
Macrophages		CD11b (n=9)	8.71 ± 0.75*
		CD172 (n=8)	12.57 ± 1.20*
		CD11b/CD172 (n=8)	6.74 ± 0.84*
		CD3/CD11b (n=4)	2.48 ± 0.62
Dendritic cells		MHC II (n=5)	10.62 ± 0.86*
		CD11c (n=9)	9.43 ± 0.57*
		MHC II/CD11c (n=5)	2.59 ± 0.52
		CD11c/CD3 (n=4)	1.76 ± 0.44
T lymphocytes		CD3 (n=17)	8.99 ± 0.33*
		CD8 (n=4)	3.58 ± 0.89
		CD3/CD8 (n=4)	1.07 ± 0.27
T regulatory lymphocytes		FoxP3 (n=6)	8.00 ± 0.56*
		CD4/FOXP3(n=6)	0.04 ± 0.12

*Expression greater than background (P ≤ 0.05).