Hereditary angioedema (HAE) due to C1-inhibitor (C1-INH) deficiency (C1-INH-HAE) is a rare, potentially life-threatening disorder characterized by recurrent swelling episodes in subcutaneous and/or submucosal tissues, which are often preceded by prodromal symptoms [
1,
2]. Forty-two to 58% of C1-INH-HAE patients have erythema marginatum (EM) as the only objective prodromal symptom of the HAE attacks [
3,
4]. Mutations in the
SERPING1 gene results in decreased C1-INH function (type 1 low C1-INH, type 2 normal or increased C1-INH protein level) [
5]. C1-INH is involved in the regulation of the complement, kallikrein-kinin, coagulation, and fibrinolytic plasma enzyme systems. The impairment of C1-INH function together with certain trigger factors can activate these cascade systems. The activation of the kallikrein-kinin system (KKS) results in cleavage of bradykinin (BK) from high molecular weight kininogen by plasma kallikrein (PKa). The release of BK increases vascular permeability, which causes angioedema by interacting with BK receptor B2 on the endothelium [
6]. A number of articles have been published to explore the pathophysiology of C1-INH-HAE, focusing on the role of plasma enzyme systems and endothelial cells [
7‐
9]. Increased white blood cell (WBC) count was observed during HAE attacks without apparent inflammatory signs. It was hypothesized that this is a consequence of hemoconcentration due to increased plasma extravasation of fluid into the extracellular space [
10‐
12]. Zotter et al
. observed that all hematologic values are increased during attacks and the elevation of WBC count is significantly greater (~ 1.5-fold) than expected based on hemoconcentration alone, and it involves specifically the peripheral blood neutrophil granulocytes (NGs) [
13]. A further study showed that neutrophil granulocyte count (NGC) is higher in C1-INH-HAE patients during symptom-free periods than in healthy controls, and this difference is further emphasized during HAE attacks. Moreover, NGs were shown to be activated during edematous episodes [
14]. It was proposed that release of NGs into the circulation contributes to the progression of HAE attacks, which may be precipitated by these cells themselves. NGs may contribute to the dysregulation of KKS, since this system can also be activated on the surface of neutrophils [
15]. NGs are capable of producing cytokines and certain enzymes, and cytokines and chemokines produced by other cell types affect their functions. NGs produce neutrophil elastase (NE), myeloperoxidase (MPO), and proteinase 3 (PRTN3) in their azurophilic granules [
16]. During activation of NGs, NE released from these cells may modify the C1-INH molecule and thereby further attenuate its already impaired function [
17,
18]. MPO is a local mediator of tissue damage and the resulting inflammation in various inflammatory diseases [
19,
20]. The primary biological function of PRTN3 depends on its proteolytic activity, which is the degradation of extracellular proteins at inflammation sites [
21]. The activation of NGs may lead to the formation of neutrophil extracellular traps (NETs) during which NGs release their DNA content and citrullinated histones decorated with the proteins from azurophilic granules (e.g., NE and MPO), specific granules, tertiary granules, and the cytoplasm to bind pathogens and also provide a negatively charged surface for the activation of the KKS and the complement systems [
22‐
26].
Moreover, activated endothelial cells and platelets may assist to the formation of NETs and the activation of NGs by producing pro-inflammatory cytokines. TNF alpha (TNFα), IL-8, and leukotriene B4 (LTB4) produced by NGs have autocrine effect on NG function itself [
27,
28]. TNFα is a cytokine involved in acute phase reactions and systemic inflammation. It is a potent chemoattractant for NGs, inducing their migration to the tissues by promoting the expression of adhesion molecules on endothelial cells [
29]. Furthermore, TNFα can induce IL-8 production from a variety of cells (e.g., endothelial cells, macrophages, neutrophils, and epithelial cells) [
28]. IL-8 is a neutrophil chemotactic factor which induces chemotaxis, primarily of NGs to the site of infection [
28,
30]. LTB4 also acts on NGs to elicit their chemotaxis and integrin-mediated adhesion to the vascular endothelium, thereby allowing them to bind to and cross into the tissue, and induces the formation of reactive oxygen species and the release of lysosomal enzymes [
31].
There is limited data on levels of peripheral blood NGs and their function in C1-INH-HAE patients. Moreover, there is very limited data on the activation of these cells during HAE attack, or their activation during EM. The latter has not been investigated until now.
The objectives of our study were (1) to confirm our previous results, on higher NGC in patients compared with healthy controls, and elevated NGC in patients during attacks, as compared with symptom-free periods; (2) to find a molecular pattern among neutrophil chemoattractants and activation markers, which may explain the distinct behavior of NGs in HAE patients; and (3) to map the neutrophil function during EM and the kinetic changes during an HAE attack, followed from the beginning until its spontaneous termination.