Effect of isoproterenol and dexamethasone on the lipopolysaccharide induced expression of CD11b on bovine neutrophils

The present experiments investigate the changes in expression of CD11b on bovine neutrophils and its modulation by isopropylnoradrenaline (IPN, isoproterenol), dexamethasone (DX), phenylephrine (α-agonist) and clenbuterol (β-agonist). Both IPN and DX caused a dose-dependent inhibition of LPS-induced CD11b expression. A combination of IPN and DX elicited a synergistical decrease of the CD11b expression. Clenbuterol mimicked the effect of IPN, whereas phenylephrine did not. The effect of IPN and DX could at least partly be mediated through a decreased TNF-α production by monocytes since tumor necrosis factor-α (TNF-α) is shown to mediate a dose-dependent CD11b up-regulation. Stimulation of stress hormone receptors partly immuno-suppresses neutrophil functions by inhibition of CD11b expression on the neutrophil surface upon LPS stimulation. This inhibition is probably related to a decrease in TNF-α production. A similar mechanism of immuno-suppression could contribute to the higher susceptibility of cattle to Gram-negative bacterial infections of the udder and lung during periods of stress.