The rationale of α1-antitrypsin (AAT) augmentation therapy to treat progressive emphysema in AAT-deficient patients is based on inhibition of neutrophil elastase; however, the benefit of this treatment remains unclear. Here we show that clinical grade AAT (with elastase inhibitory activity) and a recombinant form of AAT (rAAT) without anti-elastase activity reduces lung inflammatory responses to LPS in elastase-deficient mice. WT and elastase-deficient mice treated with either native AAT or rAAT exhibited significant reductions in infiltrating neutrophils (23% and 68%), lavage fluid levels of TNF-α (70% and 80%), and the neutrophil chemokine KC (CXCL1) (64% and 90%), respectively. Lung parenchyma TNF-α, DNA damage-inducible transcript 3 and X-box binding protein-1 mRNA levels were reduced in both mouse strains treated with AAT; significantly lower levels of these genes, as well as IL-1β gene expression, were observed in lungs of AAT-deficient patients treated with AAT therapy compared with untreated patients. In vitro, LPS-induced cytokines from WT and elastase-deficient mouse neutrophils, as well as neutrophils of healthy humans, were similarly reduced by AAT or rAAT; human neutrophils adhering to endothelial cells were decreased by 60–80% (P< 0.001) with either AAT or rAAT. In mouse pancreatic islet macrophages, LPS-induced surface expression of MHC II, Toll-like receptor-2 and -4 were markedly lower (80%,P< 0.001) when exposed to either AAT or rAAT. Consistently, in vivo and in vitro, rAAT reduced inflammatory responses at concentrations 40- to 100-fold lower than native plasma-derived AAT. These data provide evidence that the anti-inflammatory and immunomodulatory properties of AAT can be independent of elastase inhibition.

Neutrophils are the predominant immune cells in human blood possessing heterogeneity, plasticity and functional diversity. The activation and recruitment of neutrophils into inflamed tissue in response to stimuli are tightly regulated processes. Alpha1-Antitrypsin (AAT), an acute phase protein, is one of the potent regulators of neutrophil activation via both -protease inhibitory and non-inhibitory functions. This review summarizes our current understanding of the effects of AAT on neutrophils, illustrating the interplay between AAT and the key effector functions of neutrophils.

Alpha-1 antitrypsin (A1AT) is an acute-phase protein, and is best known as an inhibitor of the serine proteases, specifically, neutrophil elastase, proteinase 3, and cathepsin G. The discovery of the connection between inherited A1AT deficiency and emphysema resulted in the concept of a proteinase–antiproteinase imbalance to explain the pathogenic mechanisms of chronic obstructive pulmonary disease, as well as the concomitant development of augmentation therapy with plasma-purified human A1AT. This proteinase–antiproteinase imbalance concept has been difficult to prove, as no single mechanism can account for the complex pathology of chronic obstructive pulmonary disease. New studies have begun to characterize A1AT as an antiinflammatory and an immunoregulatory protein, independent of its antiprotease activity. We recently found that A1AT binds to free fatty acids, and it is this form of A1AT that induces the expression and release of angiopoietin-like protein 4, a protein associated with dyslipidemia and inflammation. This latter finding further strengthens the idea that describing A1AT therapy as antiserine protease is perhaps an oversimplification. The preliminary findings suggest that A1AT could be used for the management of diseases not necessarily related to inherited A1ATD, and points toward a need for more detailed investigations into the relationships between the concentration, structure, and function of A1AT protein.