Oxidative burst and Dectin-1-triggered phagocytosis affected by norepinephrine and endocannabinoids: implications for fungal clearance under stress

Abstract

A prolonged stress burden is known to hamper the efficiency of both the innate and the adaptive immune systems and to attenuate the stress responses by the catecholaminergic and endocannabinoid (EC) systems. Key mechanisms of innate immunity are the eradication of pathogens through phagocytosis and the respiratory burst. We tested the concentration-dependent, spontaneous and stimulated (via TNFα and N-formylmethionine-leucyl-phenylalanine) release of reactive oxygen species (ROS) by human polymorphonuclear leukocytes (PMNs) in vitro in response to norepinephrine (NE) and AM1241, a pharmacological ligand for the EC receptor CB2. We evaluated phagocytosis of Dectin-1 ligating zymosan particles and tested the cytokine response against Candida antigen in an in vitro cytokine release assay. Increasing concentrations of NE did not affect phagocytosis, yet stimulated ROS release was attenuated gradually reaching maximum suppression at 500 nM. Adrenergic receptor (AR) mechanisms using non-AR-selective (labetalol) as well as specific α-(prazosin) and β-(propranolol) receptor antagonists were tested. Results show that only labetalol and propranolol were able to recuperate cytotoxicity in the presence of NE, evidencing a β-receptor-mediated effect. The CB2 agonist, AM1241, inhibited phagocytosis at 10 µM and spontaneous peroxide release by PMNs. Use of the inverse CB2 receptor agonist SR144528 led to partial recuperation of ROS production, confirming the functional role of CB2. Additionally, AM1241 delayed early activation of monocytes and induced suppression of IL-2 and IL-6 levels in response to Candida via lower activity of mammalian target of rapamycin (mTOR). These findings provide new insights into key mechanisms of innate immunity under stressful conditions where ligands to the sympatho-adrenergic and EC system are released.

Stress Related Shift Toward Inflammaging in Cosmonauts After Long-Duration Space Flight

“…It appears that EC release is stimulated by conditions in space and not by the acute stress exerted during landing, which is well in line with the knowledge that acute and chronic stresses exert very different effects on the immune system (Moynihan, 2003). Correspondingly, our data show similarities to previously reported results, where the ECS was responsible for the modulation of constant baseline ROS release (without stimulus) in neutrophils and did not alter ROS production after stimulation with fMLP and TNF (Buchheim et al, 2018).…”

“…The ECS is an important stress response system and has multiple roles in a myriad of physiological processes of stress (Chouker et al, 2010; Dlugos et al, 2012; Hauer et al, 2013; Neumeister et al, 2015), metabolism (Campolongo et al, 2009), sleep and activity patterns (Richard et al, 2009; Feuerecker et al, 2012). Most importantly, endocannabinoids are potent immune modulators (Sardinha et al, 2014; Buchheim et al, 2018). They act via the endocannabinoid receptors (CB) 1 and 2, which are not only expressed in the central and peripheral nervous systems (CB1), but also on the surface of many leukocytes (CB2).…”

“…Moreover, IL-1β levels were significantly elevated in flight but dropped rapidly post-flight, indicating that the measured overshoot response was not biased simply due to higher plasma concentrations of the cytokine. Previously, we have shown that under ECS activation the fungal antigen response is abrogated (Buchheim et al, 2018). Here, we observe that plasma cytokine concentrations do not necessarily correlate with the cytokine response after antigen stimulation.…”

“…Short-term exposure to altered gravity, such as during a parabolic flight, induces the increased release of compounds of the ECS such as anandamide/N-arachidonylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) in blood (Chouker et al, 2010). Recently, the capability of the ECS to alter immune function is studied intensively and it was shown that endocannabinoids (EC) can exert a strong suppression of innate and adaptive immune responses (Buchheim et al, 2018). The effects of long-term spaceflight on EC blood levels and their participation in the adaptation process aboard are unknown.…”

Immune System Dysregulation During Spaceflight: Potential Countermeasures for Deep Space Exploration Missions

“…In murine macrophages, NE and E progress the development of a M2 regulatory phenotype in LPS co-culture via β-AR signaling, leading to an anti-inflammatory Th2 reaction ( 119 ). Since the ROS metabolism in response to different stimuli is key to survival, it is worth noting that stimulated H 2 O 2 release in granulocytes was significantly inhibited by NE in a dose-dependent manner ( 120 ) and that β-AR activation by NE was the primary mechanism to inhibit the fLMP-induced respiratory burst response in vitro . Gene expression data indicates that β1 receptor subtypes might play a pivotal role.…”