Characterisation of alpha-1 antitrypsin protein expression and secretion in natural killer cells from healthy volunteers and alpha-1 antitrypsin deficiency patients

Introduction: Alpha-1 antitrypsin (AAT) protein is the most abundant protease inhibitor in serum, but it also presents immunomodulator and anti-inflammatory activity. AAT expression is codified by the SERPINA1 gene. Mutations in this gene lead to AAT deficiency (AATD), a highly underdiagnosed respiratory condition. AAT is mainly produced by hepatocytes and, in smaller quantities, by neutrophils, monocytes, or alpha and beta-pancreatic cells, among others. Natural killer cells (NK) are a type of lymphocyte of the innate immune system. Their main function is to kill infected cells and help regulate immune response by cytokine secretion. The present study aims to characterise NK cells regarding AAT expression, due to the implication of both cells and protein, in the immune system response and regulation. Methods: NK cells were isolated from whole blood by immunomagnetic negative selection from five healthy donors and seven AATD patients. Total RNA and proteins were isolated from NK cells and AAT expression was assayed by RT-qPCR and Western Blotting. To determine AAT secretion, NK cells were cultured for 72 hours and AAT levels were determined from culture supernatants by ELISA. Results:SERPINA1 gene expression was detectable by RT-qPCR, showing similar expression levels to the GAPDH constitutive gene. AAT protein was detected by western blot in cell lysates and by ELISA in culture supernatants. Conclusion: For the first time, we have shown that AAT is expressed and secreted by NK cells derived from healthy individuals and AATD patients. Funded by 2016 Sociedad Valenciana de Neumología grant, SEPAR grant, GVA grant ACIF/2019/231