Irma Saulle ^1* Fiona Limanaqi ¹ Micaela Garziano ¹ Maria Luisa Murno ¹ Valentina Artusa ¹ Sergio Strizzi ¹ Matteo Giovarelli ¹ Carsten Schulte ¹ Jacopo Aiello ¹ Mario Clerici ^1,2 Claudia Vanetti ¹ Mara Biasin ^1*

• ¹ University of Milan, Milan, Italy
• ² Fondazione Don Carlo Gnocchi Onlus (IRCCS), Milan, Lombardy, Italy

Endoplasmic reticulum aminopeptidases 1 (ERAP1) and 2 (ERAP2) modulate a plethora of physiological processes for the maintenance of homeostasis in different cellular subsets at both intra and extracellular level. In this frame, the extracellular supplementation of recombinant human (rh) ERAP1 and ERAP2 (300ng/ml) was used to mimic the effect of stressor-induced secretion of ERAPs on neutrophils isolated from 5 healthy subjects. Following 3h or 24h-exposure we observed that rhERAPs: i) were internalized by neutrophils; ii) triggered their activation as witnessed by increased percentage of MAC-1 + CD66b + expressing neutrophils, cytokine expression/release (IL-1, IL-8, CCL2, TNF, IFN, MIP-1) and granule enzyme secretion (myeloperoxidase, Elastase); iii) increased neutrophil migration capacity; iv) increased autophagy and phagocytosis activity; v) reduced ROS accumulation and did not influence oxygen consumption rate.Our study provides novel insights into the biological role of ERAPs, and indicates that extracellular ERAPs, contribute to shaping neutrophil homeostasis by promoting survival and tolerance in response to stress-related inflammation. This information could contribute to a better understanding of the biological bases governing immune responses, and to designing ERAP-based therapeutic protocols to control neutrophil-associated human diseases.