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This in vitro study examined the ability of important immune modulators β-hydroxybutyrate (BHB), cortisol, prolactin, isoproterenol and insulin to influence the responsiveness of peripheral blood mononuclear cells (PBMC) from multiparous dairy cows 29 ± 2 days before and 14 ± 3 days after calving. The activation and proliferation of PBMC in response to the mitogen phytohemagglutinin was estimated by the oxygen consumption rate after 24 hr and the MTT (3-4,5-dimethylthiazol-2-yl-2,5diphenyl tetrazolium bromide) method after 72 hr respectively. In early lactation, the presence of 2 compared to 0.5 mmol/L BHB reduced PBMC activation (p < 0.05) and proliferation (p < 0.10), and the presence of 0.7 compared to 0.2 ng/ml insulin enhanced (p < 0.10) PBMC proliferation. In dry cows, the presence of low concentrations of BHB and insulin and both concentrations of prolactin (20 vs. 300 ng/ml) and isoproterenol (70 vs. 130 ng/L) enhanced activation (p < 0.10), but not proliferation (p ≥ 0.10) compared to cultures with no modulator addition. The presence or absence of high or low concentrations of hydrocortisone (20 vs. 45 nmol/L) did not (p ≥ 0.10) influence the activation and proliferation of PBMC from dry and early lactating cows. It is tempting to speculate that in antepartum PBMC the modulators represented an energy source or positive extrinsic signals to use nutrients for the activation process. On the other hand, PBMC from postpartum cows are known to be exposed to a metabolic challenging endocrine background. Under such conditions, high BHB concentrations and high insulin concentrations seem to act as negative and positive signals for PBMC, respectively, to utilize nutrients for activation and proliferation.
Wang et al. (Fri,) studied this question.