Voesenek, C. J. | Search bioRxiv

bioRxiv2021

Street RABV induces the cholinergic anti-inflammatory pathway in human monocyte-derived macrophages by binding to nAChr-a7, and upregulates the M2-c marker CD163

Rabies virus (RABV) is able to reach the central nervous system (CNS) without triggering a strong immune response, using multiple mechanisms to evade and suppress the host immune system. After infection via a bite or scratch from a rabid animal, RABV comes into contact with macrophages, which are the first antigen-presenting cells (APCs) that are recruited to the area and play an essential role in the onset of a specific immune response. It is poorly understood how RABV affects macrophages, and if the interaction contributes to the observed immune suppression. This study was undertaken to characterize the interactions between RABV and human monocyte-derived macrophages (MDMs). We showed that street RABV does not replicate in human MDMs. Using a recombinant trimeric RABV glycoprotein (RABV-tG) we showed binding to the nicotinic acetylcholine receptor alpha 7 (nAChr [a]7) on MDMs, and confirmed the specificity using the nAChr [a]7 antagonist alpha-bungarotoxin ([a]-BTX). We found that this binding induced the cholinergic anti-inflammatory pathway (CAP), characterized by a significant decrease in tumor necrosis factor [a] (TNF-[a]) upon LPS challenge. Using confocal microscopy we found that induction of the CAP is associated with significant cytoplasmic retention of nuclear factor {kappa}B (NF-{kappa}B). Co-cultures of human MDMs exposed to street RABV and autologous T cells further revealed that the observed suppression of MDMs affects their function as T cell activators as well, as we found a significant decrease in proliferation of CD8+ T cells. Lastly, using flow cytometric analysis we observed a significant increase in expression of CD163, hinting that street RABV is able to polarize macrophages towards a M2-c anti-inflammatory phenotype. Taken together, these results show that street RABV is capable of inducing an anti-inflammatory state in human macrophages, which affects T cell proliferation. Author summaryRabies virus (RABV) is transmitted by a bite or a scratch from an infected animal. Infection leads to a lethal encephalitis and once clinical symptoms occur, there is no effective treatment available. The virus is able to travel from the initial site of infection to the central nervous system without triggering a strong immune response, using multiple mechanisms to evade and suppress the immune system. Up to present it is unclear when and where this immunosuppression is initiated, and if local immune cells are involved as well. Understanding the complete mechanisms of immunosuppression by RABV is essential for the development and improvement of effective post-exposure treatments. In this paper we studied if RABV is able to suppress human primary macrophages as these will be the first antigen-presenting cells that are recruited to the site of infection, and are known to be important in initiating an efficient immune response. We show that RABV is able to bind, but not infect, human macrophages. Binding induces an anti-inflammatory pathway, which leads to limited T cell proliferation and directs macrophages towards and anti-inflammatory state. These results show that RABV-macrophage interactions might indeed be one of the early steps in the onset of RABV-induced immunosuppression.

immunology↗

bioRxiv2019

Reorientation and propulsion in fast-starting zebrafish larvae: an inverse dynamics analysis

Most fish species use fast starts to escape from predators. Zebrafish larvae perform effective fast starts immediately after hatching. They use a C-start, where the body curls into a C-shape, and then unfolds to accelerate. These escape responses need to fulfil a number of functional demands, under the constraints of the fluid environment and the larvas body shape. Primarily, the larvae need to generate sufficient escape speed in a wide range of possible directions, in a short-enough time. In this study, we examined how the larvae meet these demands. We filmed fast starts of zebrafish larvae with a unique five-camera setup with high spatiotemporal resolution. From these videos, we reconstructed the three-dimensional swimming motion with an automated method and from these data calculated resultant hydrodynamic forces and, for the first time, 3D torques. We show that zebrafish larvae reorient mostly in the first stage of the start by producing a strong yaw torque, often without using the pectoral fins. This reorientation is expressed as the body angle, a measure that represents the rotation of the complete body, rather than the commonly used head angle. The fish accelerates its centre of mass mostly in stage 2 by generating a considerable force peak while the fish \"unfolds\". The escape direction of the fish correlates strongly with the amount of body curvature in stage 1, while the escape speed correlates strongly with the duration of the start. This may allow the fish to independently control the direction and speed of the escape.\n\nSummary statementFish larvae can independently adjust the direction and speed of their fast start escape response, a manoeuvre crucial for survival.

biophysics↗