Methyl donor supply to heat stress-challenged polymorphonuclear leukocytes from lactating Holstein cows enhances 1-carbon metabolism, immune response, and cytoprotective gene network abundance

[EN] Mechanisms controlling immune function of dairy cows are dysregulated during heat stress (HS). Methyl donor supply-methionine (Met) and choline (Chop-positively modulates innate immune function, particularly antioxidant systems of polymorphonuclear leukocytes (PMN). The objective of this study was to investigate the effect of Met and Chol supply in vitro on mRNA abundance of genes related to 1-carbon metabolism, inflammation, and immune function in short-term cultures of PMN isolated from mid-lactating Holstein cows in response to heat challenge. Blood PMN were isolated from 5 Holstein cows (153 +/- 5 d postpartum, 34.63 +/- 2.73 kg/d of milk production; mean +/- SD). The PMN were incubated for 2 h at thermal-neutral (37 degrees C; TN) or heat stress (42 degrees C; HS) temperatures with 3 levels of Chol (0, 400, or 800 mu g/mL) or 3 ratios of Lys:Met (Met; 3.6:1, 2.9:1, or 2.4:1). Supernatant concentrations of IL-1 beta, IL-6, and tumor necrosis factor-alpha were measured via bovine-specific ELISA. Fold-changes in mRNA abundance were calculated separately for Chol and Met treatments to obtain the fold-change response at 42 degrees C (HS) relative to 37 degrees C (TN). Data were subjected to ANOVA using PROC MIXED in SAS (SAS Institute Inc., Cary, NC). Orthogonal contrasts were used to determine the linear or quadratic effect of Met and Chol for mRNA fold-change and supernatant cytokine concentrations. Compared with PMN receiving 0 mu g of Chol/mL, heat-stressed PMN supplemented with Chol at 400 or 800 mu g/mL had greater fold-change in abundance of CBS, CSAD, GSS, GSR, and GPX1. Among genes associated with inflammation and immune function, fold-change in abundance of TLR2, TLR4, IRAK1, IL1B, and IL10 increased with 400 and 800 mu g of Chol/mL compared with PMN receiving 0 mu g of Chol/mL. Fold-change in abundance of SAHH decreased linearly at increasing levels of Met supply. A linear effect was detected for MPO, NFKB1, and SOD1 due to greater fold-change in abu