The transition from acute to chronic inflammation

IL-33/regulatory T cell axis triggers the development of a tumor-promoting immune environment in chronic inflammation

Chronic inflammation's tumor-promoting potential is well-recognized; however, the mechanism underlying the development of this immune environment is unknown. Studying the transition from acute, tumor-suppressive to chronic, tumor-promoting allergic contact dermatitis (ACD) revealed how tumor-promoting chronic inflammation develops. Epidermis-derived interleukin (IL)-33 up-regulation and its induction of regulatory T cell (Treg) accumulation in the skin preceded the transition from acute to chronic ACD and triggered the tumor-promoting immune environment in chronic ACD. Mice lacking IL-33 were protected from chronic ACD and its skin cancer sequela compared with wild-type controls (P = 0.0002). IL-33's direct signaling onto Tregs was required for the development of the tumor-promoting immune environment in the skin. IL-33-Treg signaling was also required for chronic colitis and its associated colorectal cancer development in a colitis model (P < 0.0001). Significantly increased IL-33 and Tregs marked the perilesional skin and colon in patients with cancer-prone chronic inflammatory diseases. Our findings elucidate the role of the IL-33/Treg axis in creating a tumor-promoting immune environment in chronic inflammatory diseases and suggest therapeutic targets for cancer prevention and treatment in high-risk patients.

Specialized pro-resolving lipid mediators in the inflammatory response: An update

A new genus of specialized pro-resolving mediators (SPM) which include several families of distinct local mediators (lipoxins, resolvins, protectins, and maresins) are actively involved in the clearance and regulation of inflammatory exudates to permit restoration of tissue homeostasis. Classic lipid mediators that are temporally regulated are formed from arachidonic acid, and novel local mediators were uncovered that are biosynthesized from ω-3 poly-unsaturated fatty acids, such as eicosapentaenoic acid, docosapentaenoic acid and docosahexaenoic acid. The biosynthetic pathways for resolvins are constituted by fatty acid lipoxygenases and cyclooxygenase-2 via transcellular interactions established by innate immune effector cells which migrate from the vasculature to inflamed tissue sites. SPM provide local control over the execution of an inflammatory response towards resolution, and include recently recognized actions of SPM such as tissue protection and host defense. The structural families of the SPM do not resemble classic eicosanoids (PG or LT) and are novel structures that function uniquely via pro-resolving cellular and molecular targets. The extravasation of inflammatory cells expressing SPM biosynthetic routes are matched by the temporal provision of essential fatty acids from circulation needed as substrate for the formation of SPM. The present review provides an update and overview of the biosynthetic pathways and actions of SPM, and examines resolution as an integrated component of the inflammatory response and its return to homeostasis via biochemically active resolution mechanisms.

The six-day-old rat air pouch model of inflammation: characterization of the inflammatory response to carrageenan

Inflammation was induced in the 6-day-old rat air pouch by injection of carrageenan. The model was characterized in terms of exudate volume, leucocyte influx, cell free protein, prostaglandin E2 levels, and granuloma formation. The time course of all these inflammatory markers, except prostaglandin E2, showed a 3-hr lag followed by a rapid increase to 8 hr. Thereafter, the rate of increase was much slower to 48 hr. Differential cell counts indicated a predominantly polymorphonuclear cell response (75%) during the first 48 hr. Prostaglandin E2 levels increased rapidly after a 3-hr lag, to a maximum of 440 +/- 140 ng/mL at 15 hr and thereafter quickly declined to 140 +/- 60 ng/mL at 21 hr. Prostaglandin E2 levels were the most sensitive inflammatory marker to (S+)-ibuprofen and were reduced dose dependently in the range 0.05 to 1 mg/kg. We have demonstrated the time course for duration of NSAID-induced reduction of prostaglandin E2 levels during inflammation in an individual animal. Rac-ibuprofen (0.1-1 mg/kg) reduced leucocyte influx at 3 and 5 hr, after which drug effects gradually diminished by 24 hr. Rac-ibuprofen at 1 mg/kg significantly reduced the volume of air pouch exudate recovered at 24 hr but had no effect on protein levels.