Helminth regulation of host IL-4Rα/Stat6 signaling: Mechanism underlying NOS-2 inhibition byTrichinella spiralis

Abstract

Gastrointestinal nematode infection is known to alter host T cell activation and has been used to study immune and inflammatory reactions in which nitric oxide (NO) is a versatile player. We previously demonstrated that Trichinella spiralis infection inhibits host inducible NO synthase (NOS-2) expression. We now demonstrate that (i) an IL-4 receptor ␣-subunit (IL-4R␣)͞Stat6-dependent but T cell-independent pathway is the key for the nematodeinduced host NOS-2 inhibition; (ii) endogenous IL-4 and IL-13, the only known IL-4R␣ ligands, are not required for activating the pathway; and (iii) treatment of RAW264.7 cells with parasitecultured medium inhibits NOS-2 expression but not cyclooxygenase 2 expression. We propose that a yet-unidentified substance is released by the nematode during the host-parasite interaction.inflammation ͉ nematode ͉ immunoregulation ͉ nitric oxide ͉ endotoxin G astrointestinal nematode infection has served as a well established model to study parasite-induced host T cell activation and cytokine regulation (1, 2). Interaction within the cytokine network plays a key role in the control of immunity and inf lammation that mediates host protective responses (3, 4). Recently, nitric oxide (NO) has been recognized as one of the most versatile players in the immune system based on several findings. (i) Producing or responding to NO is a major feature of macrophages and many other immunesystem cells. (ii) All isoforms of NO synthase (NOS) are expressed in the immune system, and induction of inducible NOS (NOS-2) has been implicated in a variety of immunologic inf lammatory conditions. (iii) NOS-2 expression is upregulated by T helper 1 (Th1) cytokines and inhibited by Th2 cytokines. In addition, the effects of NO are not restricted to any single cytokine receptor. Thus, NO plays a very diverse role in the immune system. (iv) Activation of NOS-2 results in the production of a high concentration of NO. Highly diffusible ⅐ NO is rapidly oxidized to reactive nitrogen species that are detrimental in several immunopathologic processes [see reviews (5-7) for further information].We have previously demonstrated that Trichinella spiralis infection induces down-regulation of NOS-2 expression (8), which has the following characteristics. (i) Local jejunal infection by T. spiralis systemically inhibits NOS-2 gene transcription, protein expression, and enzyme activity in the ileum, jejunum, colon, kidney, lung, and uterus. (ii) The effect of inhibition is potent and can override endotoxin-induced NOS-2 expression. (iii) The inhibition does not extend to the expression of other isoforms of NOS; to paxillin, a housekeeper protein; or to cyclooxygenase 2 (COX-2), another protein induced by proinflammatory cytokines. (iv) The inhibition is not associated with a chemically induced intestinal inflammatory response. (v) The inhibition is unlikely related to the formation of specific antiparasite antibodies. (vi) The inhibition may involve substances other than stress-induced corticosteroids.The objective of the current...

Proteomic Modification by Nitric Oxide

“…More recently, our study with a variety of genetically modified mice has shed new light on our path to identify this selective NOS-2 inhibitor. We have demonstrated (10,27) that inhibition of NOS-2 expression by T. sprialis infection is dependent on the signaling pathway that includes the interleukin (IL)-4 receptor α subunit, receptor-associated kinases, Janus tyrosine kinase, and Stat6 in the suppression of NOS-2. It is surprising that activation of the IL4Rα/ Stat6 pathway is T-cell-independent, and is not affected by lack of endogenous IL-4.…”

“…So far, two major categories of NOS-2 inhibitors have been developed: 1) L-arginine analogues, which show limited isoform selectivity and affect the substrate for all NOS enzyme (24,25), and 2) guanidine inhibitor (aminoguanidine), which has some selectivity towards NOS-2 inhibition, but has low efficacy and causes severe side effects (25,26). The recent discovery made by us indicates that an alternative approach is possible (10,27). We have found NOS-2 expression can be selectively down regulated by Trichinella spiralis (T. spiralis, a helminth) infection (10,27).…”

“…The recent discovery made by us indicates that an alternative approach is possible (10,27). We have found NOS-2 expression can be selectively down regulated by Trichinella spiralis (T. spiralis, a helminth) infection (10,27). The features of this inhibition include the following: a) Systemic: local jejunal infection by T. spiralis induces systemic inhibition of NOS-2 expression in the ileum, colon, kidney, lung and uterus; b) mRNA level inhibition: inhibition of NOS-2 expression appears to be regulated at gene transcriptional level.…”

Helminth Infection and Type 1 Diabetes

“…Eggs hatch inside the female uterus and new larvae migrate through blood vessels to the striated muscles, where new cysts are formed. During this process, products excreted/secreted (ES) by T. spiralis induce profound effects on the host immune system, deviating Th1 responses to Th2 by inducing dendritic cells (DCs) and macrophages to acquire an immature, tolerogenic phenotype [34][35][36][37]. In addition to Th2 biasing, T. spiralis induces secretion of IL-10 and TGF-β by both innate and adaptive immune populations, contributing to regulation and containment of host tissue inflammation and fostering tissue repair [34,38].…”

In vivo inhibition of inducible nitric oxide synthase by aminoguanidine influences free radicals production and macrophage activity in Trichinella spiralis infected low responders (C57BL/6) and high responders (BALB/c) mice

“…Modulation of free radicals production by AG treatment is a good tool for studying the role of these substances during trichinellosis, because only iNOSderived NO can play role in infected host organisms besides potential side-effects of AG administration are negligible (Misko et al, 1993). It is known that iNOS activity is changing during T. spiralis infection (Bian et al, 2001;Bian et al, 2005), so the inhibition of this enzyme by AG affects cytotoxic activity of macrophages, which could play role during infection. Our previous study showed that also macrophages play important role during intestinal phase of infection as well as revealed some new information about the role of free radicals during T. spiralis infection (Kołodziej-Sobocińska et al, 2006a,b) and reinfection (Kołodziej-Sobocińska et al, 2007).…”