The roles and diversity of alarmins in the mucosae

Alarmins, a group of molecules that function to signal cell stress or death, are a key regulator of the immune response to localized insults. A tissue type often exposed to challenging conditions is the mucosa. As mucosal tissues commonly serve as a barrier between the host and the external environment, they are frequently exposed to cellular stress in the form of commensal and pathogenic microbes. Furthermore, certain mucosae are also responsible for the uptake of nutrients and other small molecules, and, thus, need to maintain a proper and tightly-regulated level of baseline selective permeability. This dual function requires constant communication between the epithelium and supporting cells formed by the local mucosal immune system, with alarmins playing a key role in this crosstalk. In this chapter, we focus on the two largest and most well-studied mucosal tissue-containing organs: the lung and the gastrointestinal (GI) tract, and present the state-of-the-art knowledge on the regulatory role of alarmins in the proper function or dysfunction of these organs.