Role of Eosinophils in Inflammatory Bowel and Gastrointestinal Diseases

Abstract

Inflammatory bowel diseases (IBD) are characterized by the invasion of leukocytes into the intestinal mucosa. However, a mixed inflammatory picture is observed that includes neutrophils, lymphocytes, monocytes, and eosinophils. To this day, the role of eosinophils in health and in disease remains unclear. Investigations into their function stem primarily from allergic diseases, asthma, and parasitic infections. This makes it even more difficult to discern a role for the fascinating eosinophil in IBDs because, unlike the lung or the skin, eosinophils reside in normal intestinal mucosa and increase in disease states; consequently, an intricate system must regulate their migration and numbers. These granulocytes are equipped with the machinery to participate in gastrointestinal (GI) inflammation and in the susceptible microenvironment, they may initiate or perpetuate an inflammatory response. A significant body of literature characterizes eosinophils present in the GI microenvironment where they have the potential to interact with other resident cells, thus promoting intestinal remodeling, mucus production, epithelial barrier, cytokine production, angiogenesis, and neuropeptide release. A number of lines of evidence support both potential beneficial and deleterious roles of eosinophils in the gut. Although studies from the gut and other mucosal organs suggest eosinophils affect mucosal GI inflammation, definitive roles for eosinophils in IBDs await discovery.

Escherichia coli strain Nissle 1917 ameliorates experimental colitis by modulating intestinal permeability, the inflammatory response and clinical signs in a faecal transplantation model

“…Eosinophils are pro-inflammatory leukocytes classically known to be associated with the Th2 cytokine profile (T-cells expressing IL-4, IL-5, IL-10 and IL-13) and which are resident in the gastrointestinal lamina propria of healthy subjects (Woodruff et al, 2011). They are recruited by chemokines that act on CCR3, especially eotaxin, and are able to secrete toxic inflammatory mediators, such as EPO, which is stored within vesicles (Al-Haddad & Riddell, 2005;Woodruff et al, 2011).…”

“…They are recruited by chemokines that act on CCR3, especially eotaxin, and are able to secrete toxic inflammatory mediators, such as EPO, which is stored within vesicles (Al-Haddad & Riddell, 2005;Woodruff et al, 2011). Eosinophils are thought to play a major pro-inflammatory role in IBD and contribute to diarrhoea, tissue destruction and fibrosis formation (Vieira et al, 2009;Albert et al, 2011).…”

Atopy and the gastrointestinal tract – a review of a common association in unexplained gastrointestinal disease

“…Although a role for IgEmediated FA remains to be conclusively shown in IBD, intestinal responses with aspects reminiscent of the allergic LPR may be seen in IBD, particularly with respect to the presence of mucosal eosinophils. There are conflicting data regarding whether mucosal eosinophils are associated with increased disease severity, tissue restitution or favorable treatment outcomes in IBD [56]. However, studies evaluating eosinophil granule proteins, indicative of eosinophil degranulation/activation, show that these proteins are increased in blood, inflammatory lesions and feces in active IBD [57][58][59][60][61].…”

CCR3 Blockade Attenuates Eosinophilic Ileitis and Associated Remodeling

“…IBD-associated fibrosis is a multifactorial process, 1,6 and although animal models indicate a role for eosinophils in acute colonic inflammation, little is known regarding the role of eosinophils in chronic ongoing ileitis or in intestinal remodeling, such as is found in patients with Crohn's disease. In this regard, eosinophils remain sources of mediators associated with fibrosis and are commonly detected in inflamed and fibrotic tissues in diseases at other sites, as well as in the gastrointestinal tract.…”