TP A7: The effect of neutrophil extracellular traps (NETs) on human neutrophils in vitro

Polymorphonuclear Neutrophil Granulocytes (PMNs) are part of the first line of defense of the innate immune system. During an inflammatory response, PMNs rapidly migrate to the site of inflammation and launch their defensive repertoire. This comprises the recruitment of further PMNs via the secretion of chemokines, phagocytosis of pathogens, and the secretion of several antimicrobial factors i.e., myeloperoxidase (MPO) and reactive oxygen species (ROS) into the inflammatory environment, in a process called degranulation [1]. Furthermore, during an inflammatory response PMNs are able to undergo a process called NETosis. During NETosis, PMNs externalize the so called Neutrophil Extracellular Traps (NETs), to capture and kill pathogens [2]. NETs are composed of decondensed chromatin fibers, which are covered with antimicrobial factors e.g. MPO, and histones [3].

However, several NET-bound proteins are known autoantigens. Thus, NETosis is linked to autoimmune diseases i.e., ANCA-associated vasculitis, systemic lupus erythematosus or rheumatoid arthritis. During these diseases, PMNs have an increased rate of activation and NETs persist in the affected tissues. Persisting NETs are suspected to serve as autoantigen-deposit sites which can be internalized by antigen-presenting cells [4]. Presentation of these NET-associated antigens to autoantigen-specific T-cells can lead to autoimmunity.

Due to the fact that PMNs themselves are able to act as antigen-presenting cells (APCs) [5], this project aims to investigate, whether neutrophils can present NET-associated autoantigens for the activation of T-cells. Since neutrophils are rapidly recruited to sites of inflammatory events, the project has the objective to shed light on early events leading to the development of autoimmunity against NET-associated autoantigens. As a first step the expression of MHC class II and co-stimulatory molecules on PMNs will be assessed after co-incubation with isolated NETs. Next the ability of NET-exposed PMNs to present model antigens such as tetanus toxoid to T-cells will be investigated. In the third step, we are going to assess the ability of PMNs to present NET-associated antigens to T-cells from patients with autoimmune diseases.

[1] Mortaz E, Alipoor SD, Adcock IM, Mumby S and Koenderman L (2018) Update on Neutrophil Function in Severe Inflammation. Front. Immunol. 9:2171.
[2] Brinkmann, V., U. Reichard, C. Goosmann, B. Fauler, Y. Uhlemann, D.S. Weiss, Y. Weinrauch, and A. Zychlinsky. 2004. Neutrophil extracellulartraps kill bacteria. Science. 303:1532–1535.
[3] Brinkmann V, Zychlinsky A. Neutrophil extracellular traps: is immunity the second function of chromatin? J Cell Biol (2012) 198(5):773–83.
[4] Papayannopoulos V. (2017) Neutrophil extracellular traps in immunity and disease. Nature Reviews Immunology volume 18, pages 134–147
[5] Park HY, Jin J, Song MG, Park JI and Kwak JY. (2007) Expression of dendritic cell markers on cultured neutrophils and its modulation by anti-apoptotic and pro-apoptotic compounds Exp. Mol. Med. Vol. 39(4), 439-449