Non specific immunity and ketone bodies. II: in vitro studies on adherence and superoxide anion production in ovine neutrophils

The effects of the ketone bodies β-OH-butyrate and acetoacetate (2.4 or 4.8 mmol/1), administered singly or simultaneously in vitro, on adherence and superoxide anion (SO) production in ovine neutrophils were investigated by simultaneous assay in 96-well microplates. Because the acetoacetate used was a lithium salt, the effect of 2.4 and 4.8 mmol/1 lithium chloride was also tested. Neutrophils from eight non-lactating, non-pregnant ewes were used. SO release from neutrophils was found to be very low in basal conditions and was apparently not stimulated by contact with plastic. Administration of 10-7 mol/l phorbol myristate acetate (PMA) caused a rapid increase and release of SO production, but smaller than that induced by co-stimulation with plastic and 10-7 mol/l PMA. LiCl (2.4 and 4.8 mmol/l) significantly increased PMA-stimulated release, but inhibited plastic and PMA co-stimulated SO release. Administration of 2.4 mmol/l ketone bodies inhibited plastic and PMA-costimulated SO release, but the effect of acetoacetate could be due to the lithium component. Administration of 4.8 mmol/l ketone bodies had no effect. Adherence was significantly increased by contact with plastic, and moreover by 10-7 mol/l PMA. The effect was similar when PMA was acting alone or with plastic. Neither basal nor stimulated adherence were affected by 2.4 or 4.8 mmol/l ketone bodies. LiCl at a concentration of 4.8 mmol/l increased PMA and plastic co-stimulated adherence. The results suggest that, in sheep, only the ketone body β-OH butyrate at concentrations seen in mild ketosis, could decrease bactericidal activity, while adherence is not affected. In addition to other factors that could impair the efficiency of the immune system in ketotic ruminants, the reduced bactericidal activity may contribute to the higher occurrence of infectious disease in these animals.