Acute-phase protein α1-anti-trypsin: diverting injurious innate and adaptive immune responses from non-authentic threats

Clin Exp Immunol. 2015 Feb;179(2):161-72. doi: 10.1111/cei.12476.


One would assume that the anti-inflammatory activity of α1-anti-trypsin (AAT) is the result of inhibiting neutrophil enzymes. However, AAT exhibits tolerogenic activities that are difficult to explain by serine-protease inhibition or by reduced inflammatory parameters. Targets outside the serine-protease family have been identified, supporting the notion that elastase inhibition, the only functional factory release criteria for clinical-grade AAT, is over-emphasized. Non-obvious developments in the understanding of AAT biology disqualify it from being a straightforward anti-inflammatory agent: AAT does not block dendritic cell activities, nor does it promote viral and tumour susceptibilities, stunt B lymphocyte responses or render treated patients susceptible to infections; accordingly, outcomes of elevated AAT do not overlap those attained by immunosuppression. Aside from the acute-phase response, AAT rises during the third trimester of pregnancy and also in advanced age. At the molecular level, AAT docks onto cholesterol-rich lipid-rafts and circulating lipid particles, directly binds interleukin (IL)-8, ADAM metallopeptidase domain 17 (ADAM17) and danger-associated molecular pattern (DAMP) molecules, and its activity is lost to smoke, high glucose levels and bacterial proteases, introducing a novel entity - 'relative AAT deficiency'. Unlike immunosuppression, AAT appears to help the immune system to distinguish between desired responses against authentic threats, and unwanted responses fuelled by a positive feedback loop perpetuated by, and at the expense of, inflamed injured innocent bystander cells. With a remarkable clinical safety record, AAT treatment is currently tested in clinical trials for its potential benefit in a variety of categorically distinct pathologies that share at least one common driving force: cell injury.

Keywords: acute-phase proteins; diabetes; transplantation.

Publication types

  • Review

MeSH terms

  • ADAM Proteins / antagonists & inhibitors
  • ADAM Proteins / immunology
  • ADAM17 Protein
  • Adaptive Immunity*
  • B-Lymphocytes / immunology*
  • B-Lymphocytes / pathology
  • Dendritic Cells / immunology*
  • Dendritic Cells / pathology
  • Female
  • Humans
  • Immune Tolerance / drug effects
  • Immunity, Innate*
  • Immunosuppression Therapy / methods*
  • Pregnancy
  • alpha 1-Antitrypsin / immunology
  • alpha 1-Antitrypsin / therapeutic use*


  • SERPINA1 protein, human
  • alpha 1-Antitrypsin
  • ADAM Proteins
  • ADAM17 Protein
  • ADAM17 protein, human