α1-Antitrypsin, old dog, new tricks -: α1-Antitrypsin exerts in vitro anti-inflammatory activity in human monocytes by elevatin cAMP

Regulation of serine protease activity is considered to be the sole mechanism for the function of alpha(1)-antitrypsin (AAT). However, recent reports of the anti-inflammatory effects of AAT are hard to reconcile with this classical mechanism. We discovered that two key activities of AAT in vitro, namely inhibition of endotoxin-stimulated tumor necrosis factor-a and enhancement of interleukin-10 in human monocytes, are mediated by an elevation of cAMP and activation of cAMP-dependent protein kinase A. As expected with this type of mechanism, the AAT mediated rise in cAMP and the impact on endotoxin-stimulated tumor necrosis factor-a and interleukin-10 was enhanced when the catabolism of cAMP was blocked by the phosphodiesterase inhibitor rolipram. These effects were still observed with modified forms of AAT lacking protease inhibitor activity.