Phosphodiesterase 4 inhibition of β2-integrin adhesion caused by leukotriene B4 and TNF-α in human neutrophils

Phosphodiesterase (PDE)4 inhibition attenuates neutrophilic inflammation in chronic obstructive pulmonary disease. The objective of the present study was to examine the efficacy and mechanism by which PDE4 inhibition blocks adhesion of beta(2)-integrin to an endothelial counterligand. Neutrophils (polymorphonuclear leukocytes (PMNs)) were isolated from humans receiving no medication. Adhesion was analysed by myeloperoxidase activity. The effects of cilomilast +/- salmeterol on the following were determined: 1) surface CD11b expression; 2) adhesion; 3) intracellular cyclic adenosine monophosphate (cAMP) concentration; and 4) extracellular signal-regulated kinase (ERK)-1/2-mediated group IVA-phospholipase A(2) (gIVA-PLA(2)) phosphorylation caused by leukotriene (LT)B-4 or tumour necrosis factor (TNF)-alpha activation. Either cilomilast or rolipram +/- salmeterol caused concentration-related blockade of LTB4-induced adhesion to counterligand, but had no effect on TNF-alpha-activated PMNs. A comparable increase in intracellular cAMP concentration for PMNs activated with LTB4 and TNF-alpha was caused by 1 mu M cilomilast and 0.1 mu M salmeterol. Upregulation of surface CD11b expression and ERK-1/2 phosphorylation were blocked by cilomilast or rolipram +/- salmeterol for PMNs activated by LTB4, but not for cells stimulated by TNF-alpha. Cilomilast +/- salmeterol also blocked gIVA-PLA(2) phosphorylation caused by LTB4 but not TNF-alpha. In conclusion, the current study demonstrates that both leukotriene B-4 and tumour necrosis factor-alpha upregulate cyclic adenosine monophosphate. However, cyclic adenosine monophosphate does not block beta(2)-integrin adhesion caused by tumour necrosis factor-a. It was concluded that tumour necrosis factor-a prevents inhibition of extracellular signal-regulated kinase-1/2-mediated group IVA-phospholipase A(2) activation, which is essential for beta(2)-integrin adhesion in polymorphonuclear leukocytes.