Interferon-Alpha Promotes Th1 Response and Epithelial Apoptosis via Inflammasome Activation in Human Intestinal Mucosa

Abstract

Backgound & AimsSeveral lines of investigation suggest that interferon (IFN) alpha can alter human intestinal mucosa homeostasis. These include the endogenous production of IFN alpha in celiac disease or inflammatory bowel diseases, as well as the occurrence of intestinal side effects of exogenous IFN alpha used as a therapeutic tool. Here, we present an ex vivo translational approach to investigate the effects of IFN alpha on the human normal intestinal mucosa, as well as its underlying mechanisms.MethodsHuman normal colonic mucosa explants were cultured in the presence or absence of IFN alpha 2a. Epithelial homeostasis was assessed using the immunohistochemical marker of apoptosis M30. The Wnt inhibitor Dickkopf-Homolog-1 (DKK1) was assayed in the supernatants by enzyme-linked immunosorbent assay. Activation of the inflammasome (caspase-1/interleukin [IL]18) and of a Th1 response was determined by in situ detection of active caspase-1, as well as by measurement of mature IL18 production and the prototype Th1 cytokine IFN gamma by enzyme-linked immunosorbent assay. In addition, mechanistic studies were performed using the specific caspase-1 inhibitor Tyr-Val-Ala-Asp(OMe)-fluoromethylketone (YVAD-FMK), IL18-binding protein, neutralizing anti–IFN gamma, and anti-DKK1 antibodies.ResultsIFN alpha 2a elicited a rapid (24 hours) disruption of surface and crypt colonic epithelial cells via apoptosis that was variable in intensity among the 20 individuals studied. This apoptotic effect was dependent on the initiation of an IFN gamma response elicited by resident T box expressed in T cells–positive lamina propria cells. Both apoptosis and Th1 response were subordinated to active caspase-1 and IL18 production. Finally, neutralization of IFN gamma–induced DKK1 partially protected against IFN alpha–induced epithelial apoptosis.ConclusionsBy using an ex vivo model, we show an interindividual heterogeneity of IFN alpha effects. We show that IFN alpha is able to disrupt both epithelial and immune homeostasis in the human intestine, by activation of an innate immunity platform, the inflammasome, which drives a Th1 response and leads to epithelial barrier disruption.

Reovirus-Induced Apoptosis in the Intestine Limits Establishment of Enteric Infection

“…Within reovirus-infected cells, NF-B and IRF-3 are required for maximum levels of apoptosis (25,(44)(45)(46). It is possible that cytokines induced by NF-B and IRF-3, including type I interferons, activate death pathways in adjacent, uninfected cells (47)(48)(49)(50). In addition, triggering enterocyte death would restrict viral replication and limit the amount of antigen observed by immunohistochemical staining.…”

The double stranded RNA analog poly-IC elicits both robust IFN-λ production and oncolytic activity in human gastrointestinal cancer cells

“…The gastrointestinal epithelial lining is the first line of defense against potentially noxious agents including bacteria, bacterial products and viruses. Based on both primary cultures of normal human intestinal epithelial cells [ 1 ] and on ex vivo explant cultures of human normal colonic mucosa we have contributed to the emergence of the concept of innate immune functions as well as immunomodulatory functions of the human intestinal mucosa epithelium [ 2 – 5 ].…”

A Perfect Match: Explant and Organoid Systems Help Study Cytokines in Sickness and Health

“…In this issue of Cellular and Molecular Gastroenterology and Hepatology , Jarry et al 1 showed that one of the type I interferons, interferon α (IFN-α), induces apoptosis and promotes intestinal epithelial barrier disruption by activating the inflammasome. The investigators used a 3-dimensional model of human normal colonic mucosa explant culture, an ex vivo system that not only maintains the architecture of the tissue but also contains various mucosal resident cells that can interact to trigger an innate immune response.…”

“…The human normal colonic explant culture allowed Jarry et al 1 to investigate how IFN-α affects intestinal mucosa homeostasis through a cross-talk between epithelial and immune cells and describe the mechanisms involved. The possibility of a direct effect of IFN-α in the human colonic epithelium, however, cannot be discarded completely.…”

“…The epithelial response to chronic inflammation has been assessed by exposing mouse colonic organoids to IL1β, IL6, tumor necrosis factor α, LPS, and flagellin for 60 weeks, resulting in persistent nuclear factor-κB activation and epithelial cell transformation 5 . The possibility of investigating interactions between different mucosal cells is an important characteristic of the explant culture used by Jarry et al, 1 while questions that require a still complex, but more isolated, epithelial-focused system benefit from organoids. Therefore, associating both explant and organoid models can help elucidate the molecular and cellular mechanisms involved in the interplay between the GI epithelium and immune cells, by determining the precise roles of intermediate cytokines in the maintenance and disturbance of tissue homeostasis.…”