Macrophages monitor tissue osmolarity and induce inflammatory response through NLRP3 and NLRC4 inflammasome activation

Interstitial osmolality is a key homeostatic variable that varies depending on the tissue microenvironment. Mammalian cells have effective mechanisms to cope with osmotic stress by engaging various adaptation responses. Hyperosmolality due to high dietary salt intake has been linked to pathological inflammatory conditions. Little is known about the mechanisms of sensing the hyperosmotic stress by the innate immune system. Here we report that caspase-1 is activated in macrophages under hypertonic conditions. Mice with high dietary salt intake display enhanced induction of Th17 response upon immunization, and this effect is abolished in caspase-1-deficient mice. Our findings identify an unknown function of the inflammasome as a sensor of hyperosmotic stress, which is crucial for the induction of inflammatory Th17 response. The inflammasomes are multiprotein structures that trigger inflammation in response to diverse stress conditions. Here, Ip and Medzhitov show that the NLRP3 and NLRC4 inflammasomes in macrophages act as sensors of hyperosmotic stress and participate in salt-induced inflammatory responses.