Cigarette smoke effects on innate immune mechanisms in the nasal mucosa. Potential effects on the microbiome

It is well established that exposure to cigarette smoke (CS), through active smoking and through exposure to secondhand smoke, has immunosuppressive effects, yet how this might affect the microbiome is not known. In this manuscript we focus on the effects of CS on innate host defense response, with particular emphasis on the role of epithelial cells and mucosal immune responses in the nose and the potential effects on the microbiome. The studies described here briefly summarize the effects of CS on specific innate immune cells, such as neutrophils, macrophages/monocytes, natural killer cells, and dendritic cells. A detailed description of how CS affects epithelial cells and why we consider this to be a central defect in the overall immunosuppressive effects of CS in the lung is provided. We summarize data on the role of the "epimmunome" in the context of CS exposure, including the effects on soluble mediator production, such as cytokines, chemokines, and antimicrobial defense mediators. Separate emphasis is put on the expression of ligands on epithelial cells, which directly interact with receptors on immune cells, and the effects of CS on these interactions. We introduce the nose and nasal mucosa as a model to study the effects of CS exposure on host defense responses and changes in the microbiome in humans in vivo. Understanding the dynamics of a healthy microbiome and how CS affects this balance is important to uncovering the mechanisms of CS-induced disease.