Up-Regulation of IL-18 and IL-12 in the Ileum of Neonatal Rats with Necrotizing Enterocolitis

Abstract

Necrotizing enterocolitis (NEC) is a common and devastating gastrointestinal disease of premature infants. Because the proinflammatory cytokines IL-18, IL-12, and interferon (IFN)-␥ have been implicated in other diseases of the small intestine, we hypothesized that these cytokines would play an important role in NEC pathogenesis. NEC was induced in newborn rats via enteral feeding with rat milk substitute and asphyxia and cold stress (RMS). Dam-fed, asphyxia-and cold-stressed littermates were used as controls (DF). After 96 h, the distal ileum was removed from all animals and processed to determine expression and localization of IL-18, IL-12, and IFN-␥ using real-time reverse transcriptase PCR and immunohistology. IL-18 and IL-12 mRNA from the RMS group were increased (p Յ 0.05) compared with DF controls, and there was a correlation between increasing IL-18 and IL-12 mRNA levels and progression of tissue damage (r ϭ 0.629 and 0.588, respectively; p Յ 0.05). NEC is the most common gastrointestinal disease of premature infants (1). Its etiology, however, remains elusive (2). It has been suggested that the major risk factors for NECprematurity, formula feeding, intestinal ischemia/hypoxia, and bacterial colonization-promote an inflammatory cascade that results in the pathology associated with this disease (3, 4). The development of animal models has been vital to the understanding of NEC (5). The neonatal rat model, where NEC is induced in newborn rats by enteral feeding of artificial formula coupled with asphyxia and cold stress, is an established model for study of this disease (6 -11).The intestinal environment is capable of producing an array of cytokines important in the development and control of inflammatory responses (12, 13). Among these, proinflammatory IL-18 (14 -17), , and IFN-␥ (21, 22) have been implicated in inflammatory diseases of the small intestine. Individually, IL-18 and IL-12 can induce small amounts of IFN-␥ from T, natural killer (NK), and B cells. Together, IL-18 and IL-12 can work synergistically to induce greater quantities of IFN-␥ from these immunocompetent cells, and IL-18 and IL-12 can induce intestinal inflammation in the presence of IFN-␥ in mice (23). Both IL-18 and IL-12 are produced by MC, however, IL-18 is produced by IEC as well (12, 24 -26).Cytokine profiles in NEC are poorly defined and sometimes contradictory. IFN-␥ mRNA showed a slight trend toward up-regulation in rats with experimental NEC (10) and was increased in infants with NEC (27, 28

Necrotizing enterocolitis: A multifactorial disease with no cure

“…IL-18 is also essential to host defense against a variety of infections [119] and is potentially important in the development of NEC. Immunohistochemistry reveals the presence of IL-18 in intestinal epithelial and lamina propria cells which correlates with the degree of tissue damage in a neonatal rat NEC model [99] . Depending on the surrounding environment, IL-18 may play a destructive or protective role in NEC.…”

“…Several pro-inflammatory cytokines that mediate inflammatory cell recruitment through activation and amplification of the immune response in local host defense have been implicated in NEC including TNF-α, IL-1β, IL-6, IL-8, IL-12, and IL-18 [99][100][101] . Antiinflammatory cytokines modulate the host's inflammatory response and if they fail to achieve their goal, proinflammatory mediators can continue, resulting in tissue injury [4] .…”

“…Compared with other inflammatory bowel syndromes, TNF-α transcripts are lower in NEC [108] . Furthermore, studies indicate that the majority of TNF-α found in the gut lumen comes from Kupffer cells in the liver [99] . Taken together, these studies suggest that TNF-α plays a less significant role in the inflammatory cascade associated with NEC as compared with other intestinal inflammatory conditions.…”

“…IL-12 is a potentially important cytokine in the development of NEC. Halpern [99] localized IL-12 via immunohistochemistry to monocytes in the intestinal mucosa and lamina propria and correlated IL-12 positive cells with tissue damage in a neonatal rat model of NEC.…”

Unexpected Macrophage Activity Alters the Inflammatory Process in Necrotizing Enterocolitis

“…Prior studies have demonstrated conflicting results regarding the production of IL-12 in rats undergoing a NEC-inducing protocol when compared to dam fed controls. While Nadler et al showed decreased IL-12 mRNA expression in NEC animals [27], Halpern et al showed an increase in IL-12 mRNA in NEC animals and a correlation between the number of IL-12 positive cells and the degree of tissue destruction [28]. The positive correlation between the number of IL-12 positive cells and the amount of tissue damage present led many to draw the conclusion that IL-12 is involved with the initial stages of NEC and may contribute to the intestinal necrosis associated with NEC [24].…”