Primary Murine Epithelial Cells Research Articles

54 Impact of Carbon Nanoparticle–Triggered Gammaherpesvirus Reactivation on Lung Immunity and Diseases

Abstract Inhalation of environmental particles and herpesvirus infection are ubiquitous in our society. Herpesviruses persist lifelong in the host in a latent state, which can be exited by stress-induced reactivation with production of lytic virus. Our previous investigations show that pulmonary exposure to carbon nanoparticles (CNP) triggers reactivation of latent murine gammaherpesvirus 68 (MHV-68) in mouse lungs, mainly localizing to CD11b+ infiltrating macrophages and dependent on p38 MAPK signaling. Furthermore, we observed that a two-time repeated CNP administration to latently infected mice resulted in alveolar damage leading to progressive emphysema. However, the underlying adverse mechanisms causing alveolar damage and the corresponding cell communication upon CNP exposure in latently infected lungs is still unclear. To investigate this, we developed a 3D lung organoid culture from primary murine epithelial cells in combination with persistently MHV-68 infected macrophages. This model enables us to detect reactivation and cytokine release upon CNP exposure, and to gain insights into the cellular communication of epithelial cells and macrophages, to understand the mechanisms underlying reactivation-triggered damage. In parallel, adverse effects of this second hit scenario on the alveolar epithelium and subsequent disease development get investigated in vivo. Latently infected mice are exposed to CNP up to 5 times, and virus reactivation and further epithelial damage is analyzed. By uncovering molecular mechanisms underlying the adverse effects and elucidating the communication occurring in vitro and in vivo we want to identify potential targets to prevent exacerbation of lung diseases caused by these two omnipresent factors, herpesvirus infection and ambient particle exposure.

Epithelial Cells Are Sensitive Detectors of Bacterial Pore-forming Toxins

Epithelial cells act as an interface between human mucosal surfaces and the surrounding environment. As a result, they are responsible for the initiation of local immune responses, which may be crucial for prevention of invasive infection. Here we show that epithelial cells detect the presence of bacterial pore-forming toxins (including pneumolysin from Streptococcus pneumoniae, alpha-hemolysin from Staphylococcus aureus, streptolysin O from Streptococcus pyogenes, and anthrolysin O from Bacillus anthracis) at nanomolar concentrations, far below those required to cause cytolysis. Phosphorylation of p38 MAPK appears to be a conserved response of epithelial cells to subcytolytic concentrations of bacterial poreforming toxins, and this activity is inhibited by the addition of high molecular weight osmolytes to the extracellular medium. By sensing osmotic stress caused by the insertion of a sublethal number of pores into their membranes, epithelial cells may act as an early warning system to commence an immune response, while the local density of toxin-producing bacteria remains low. Osmosensing may thus represent a novel innate immune response to a common bacterial virulence strategy.