Mesenteric fat in Crohn's disease: a pathogenetic hallmark or an innocent bystander?

n the first half of the 20th century, white adipose tissue (WAT) was mainly viewed as an isolated tissue protecting the organism from heat loss and a passive energy storage compartment.Similarly to other species such as Drososophila melanogaster, it is now well recognised that mammalian fat tissue is not solely a reservoir for excess nutrients but also an active and dynamic organ involved in the development of metabolic syndromes and the regulation of immunity and inflammation.The older anatomical literature repeatedly mentions a close association between adipose tissue and lymphoid organs in various mammals including humans, suggesting a potential role of WAT in the host immune response.Several recent studies indicate that adipocytes could function as macrophage-like cells 1 as they express receptors related to the innate immune system and secrete major mediators of inflammation, such as tumour necrosis factor alpha (TNFa).Consistent with this hypothesis, 2 the biology of adipocytes is particularly implicated in chronic diseases, such as obesity 3 and atherosclerosis. 4 This review will focus on the normal and pathophysiological functions of mesenteric WAT (mWAT), which may play an important role in the inflammatory and fibrotic processes in Crohn's disease, a frequent and complex form of inflammatory bowel disease (IBD). ENDOCRINE AND IMMUNE FEATURES OF ADIPOCYTES cLong considered as the ''anatomists' Cinderella'', 5 mWAT is now recognised as a multifunctional organ.Notably located around organs such as the gut or the lungs, adipocytes may have evolved strategies to drive immune responses to microbial invaders by expressing different innate immune sensors.In addition its function as a storage organ, WAT plays a major endocrine and immune role by expressing several hormones and various mediators (fig 1).To clarify the nomenclature, we will refer to the hormones and immunomodulatory molecules derived from adipocytes as adipormones and adipocytokines, respectively.