Differential regulation of expression of the MHC class II molecules RT1.B and RT1.D on rat B lymphocytes: effects of interleukin-4, interleukin-13 and interferon-gamma

Morphine suppresses MHC-II expression on circulating B lymphocytes via activation of the HPA

Morphine has been shown to alter gene expression of the major histocompatibility complex, class II (MHC-II) in circulating rat immunocytes. Here, we demonstrate that a single morphine injection (10 mg/kg) reduces basal MHC-II protein expression on circulating B lymphocytes by 33%, while also impairing the ability of B lymphocytes to increase MHC-II upon interleukin-4 induction. As these data implicate opioids in the regulation of antigen presentation, studies were undertaken to examine the potential mechanisms through which morphine exerts this suppressive effect. Central injection studies utilized Tyr-D-Ala-Gly-(me) Phe-Gly-ol (DAMGO), an opioid receptor agonist, which mimicked morphine's effect on MHC-II, while D-Phe-Cys_Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP) pretreatment, prior to morphine, blocked the suppression of MHC-II. As central opioid receptor activation results in the activation of the hypothalamic-pituitary-adrenal axis, thereby, signaling increased circulating corticosterone levels, we examined whether MHC-II expression was suppressed after incubation with corticosterone at concentrations similar to those observed after morphine. Interestingly, corticosterone dramatically decreased basal MHC-II (88%) expression while completely preventing the induction of MHC-II. Additionally, MHC-II suppression was absent in morphine-treated adrenalectomized animals. Since prolonged morphine exposure has previously been shown to result in tolerance to both the steroidogenic and immunosuppressive effects of morphine, the effect of prolonged morphine exposure on MHC-II was also examined. Interestingly, MHC-II expression is no longer suppressed after chronic morphine, while morphine withdrawal results in both a renewed increase in circulating corticosterone levels and a renewed suppression of MHC-II in previously tolerant animals. Taken together, these data strongly implicate corticosterone in mediating the suppressive effects of morphine on circulating B-lymphocyte MHC-II expression.

IL-13 prolongs allograft survival: Association with inhibition of macrophage cytokine activation

Th2 cytokines, especially IL-4 and IL-10, may facilitate transplant tolerance induction but the role of IL-13, another Th2 cytokine, is not known. This study examined the effects of rat recombinant IL-13 (rIL-13) on alloimmune responses. In vitro effects of rIL-13 were compared in mixed lymphocyte cultures (MLC) on rat lymphocytes cultured with PVG stimulator cells. DA rats grafted with fully allogeneic PVG neonatal heart grafts were treated with 40,000 units of rIL-13 for 10 days and graft survival monitored by ECG. Cytokine mRNA expression in the graft and lymphoid tissues was studied by RT-PCR and alloantibody levels assayed. rIL-13 had no effect on MLC, unlike rIL-4 which enhanced proliferation and induced Th2 and inhibited Th1 cytokines in MLC. rIL-13 inhibited IL-12p35, IL-12p40 and TNF-alpha mRNA induction in dendritic cell cultures. Treatment with rIL-13 prolonged fully allogeneic PVG neonatal heart graft survival to 18-21 (13-27) days (median (range)); compared to 12 (9-15) days in untreated normal rejection (p<0.05) and 14 (10-24) days in sham treated controls (p<0.05). RT-PCR studies on graft tissue identified reduced mRNA expression for the dendritic cell/macrophage molecules iNOS, TNF-alpha and IL-12 compared to normal rejection. rIL-13 treatment did not increase Th2 cytokines as compared to normal rejection, or the Th2 dependent IgG1 alloantibody response, while IL-4 did. These studies demonstrated that rIL-13 can prolong allograft survival associated with inhibition of IL-12, TNF-alpha and iNOS mRNA induction, and suggest IL-13 could modify graft rejection by inhibition of dendritic cell and/or macrophage function.

Interleukin-12p70 Prolongs Allograft Survival by Induction of Interferon Gamma and Nitric Oxide Production

BACKGROUND

Interleukin (IL)-12p70, a heterodimeric cytokine has been considered central to induction of Th1 responses with the assistance of IL-18 and IL-27. It was predicted IL-12p70 treatment would promote allograft rejection. In these studies, IL-12p70 delayed rejection.

METHODS

We compared Piebald Virol Glaxo (PVG) neonatal heart graft survival in fully allogeneic Dark Agoutti (DA) rats treated with IL-12p70 alone or in combination with other cytokines. The mechanism by which IL-12p70 induced delayed rejection was examined by reverse transcription polymerase chain reaction of cytokine mRNA and studying the role of interferon (IFN)-gamma and inducible nitric oxide synthase (iNOS) that were induced by IL-12.

RESULTS

IL-12p70 treatment significantly delayed PVG neonatal heart graft rejection compared to normal rejection control and other control groups treated with supernatant from Chinese hamster ovary (CHO)-K1 cells transfected with IL-12p35, IL-12p40, or no cytokine gene. IL-12p70 had no effect on alloantibody response. IFN-gamma and iNOS mRNA expression was increased in heart graft and regional lymph node compared to normal rejection and other treatment groups, consistent with Th1 response induction. IL-12p35 mRNA expression decreased in IL-12p70 treated rats but there was no difference in IL-12p40, Th2, or Tr1 cytokine mRNA expression. Coadministration of an iNOS inhibitor, L-NIL, or a monoclonal antibody (mAb) that blocks IFN-gamma, inhibited IL-12p70's ability to prolong allograft survival; as did co-treatment with IL-4 but not IL-13.

CONCLUSIONS

IL-12p70 treatment may inhibit rejection by hyperinduction of Th1 responses, especially production of IFN-gamma and nitric oxide. These effects may be by enhancing regulatory T-cell responses or by the activation of iNOS in macrophages to produce excessive nitric oxide that in turn inhibits alloimmune responses.

Systemic Morphine Administration Suppresses Genes Involved in Antigen Presentation

Administration of opioids in both humans and animal models results in significant alterations in immune system responsiveness. Although the majority of studies have focused on phenotypic changes in immune cells after short- and long-term morphine administration, few studies have determined whether alterations in gene expression profiles accompany these effects. To address this question, rats were treated with either morphine (20 mg/kg) or saline, and changes in gene expression and function in blood leukocytes were examined. Within 2 h, morphine administration resulted in a decrease in blood leukocyte expression of the major histocompatibility complex class II (MHC II RT1.B beta) (-3.27-fold) and related molecules, including the MHC II invariant chain (-2.73-fold). Furthermore, these changes in gene expression were accompanied by a significant decrease in surface MHC II RT1.B beta protein expression, specifically on B lymphocytes. Morphine administration was also found to inhibit IL-4 induced up-regulation of MHC II RT1.B beta cell surface expression on B lymphocytes. This is the first demonstration that receptors involved in antigen presentation are modified after systemic morphine administration. We propose that the inability of B lymphocytes to up-regulate key immune proteins, such as the MHC II molecule, after exposure to antigen-induced cytokine production may account for the increase in the susceptibility to bacterial and viral infections such as HIV in both drug abusers and patients receiving morphine.

Ectopic expression of MHC class II genes (RT1.B(I) beta/alpha) in rat hepatocytes in vivo and in culture can be elicited by treatment with the pregnane X receptor agonists pregnenolone 16 alpha-carbonitrile and dexamethasone

The synthetic steroid, pregnenolone-16-alpha-carbonitrile (PCN), has served for decades as a probe for a postulated series of hepatic defenses activated under situations of environmental "stress". PCN, an antiglucocorticoid, and also such glucocorticoids as dexamethasone (Dex) appear to stimulate hepatic metabolism and elimination of xenobiotics by binding to the nuclear pregnane X receptor (PXR) which then interacts with a distinct DNA response element associated with induction of cytochrome P450 3A genes. To explore the full domain of genes controlled by PCN/PXR, we used differential display to detect rat liver mRNA species selectively induced by PCN or by Dex. Sequence analysis identified one of many PCN induced cDNA fragments as RT1.B(I)beta, a member of the major histocompatability class II (MHC) gene family usually found only in antigen presenting cells. Northern blot analysis of RNA from rat liver or from cultured hepatocytes confirmed that amounts of RT1.B(I)beta mRNA and also of its companion gene, RT1.B(I)alpha mRNA, became readily detectable within 3-6 hours following treatment with PCN or Dex, whereas no induction was observed in spleen RNA. Induction by PCN of RT1.B(I)beta immunoreactive protein was localized to the hepatocytes as judged by immunofluorescence. We conclude that ectopic expression of MHC II genes, an unprecedented effect of steroids or drugs, is rapidly evoked by PCN acting on the liver, directly. The concept of a set of genes coordinately controlled to maintain homeostasis in parenchymal tissues during toxic stress must now be extended to include the immune system.

Mercuric chloride enhances immunoglobulin E-dependent mediator release from human basophils

Mercuric chloride (HgCl2) is an industrial agent known to cause autoimmune disorders and induce IgE synthesis, which plays a crucial role in the manifestation of allergic diseases. In rodents, the immunomodulatory effects of HgCl2 have been shown to involve the enhancement of mast cell-derived IL-4 secretion, which facilitates both Th2-lymphocyte development and IgE production. In humans, rapid allergen-dependent release of IL-4 and the related cytokine IL-13 from histamine-containing cells occurs primarily in basophils, along with other proinflammatory mediators such as histamine and LTC4. In this study, we therefore investigated the effects of HgCl2 on the release of the above basophil mediators, either due to the compound alone or in conjunction with IgE-dependent stimulation. HgCl2 (10(-9) to 10(-6) M) did not induce mediator secretion alone but significantly enhanced the release of histamine, LTC4, IL-4, and IL-13 caused by anti-IgE. Higher concentrations of HgCl2 (10(-5) to 10(-3) M) strikingly reduced cell viability; however, toxicity varied depending on cell density and incubation time. Removal of HgCl2 following a short incubation with basophils did not reverse the potentiating effects on basophil mediator secretion to anti-IgE and the concentration of free mercury in the supernatants significantly diminished by up to 20% after incubation with the cells, indicating irreversible Hg binding to cells. By upregulating IgE-dependent human basophil mediator release, our results clearly indicate that HgCl2 potentially exacerbates allergic disorders and promotes a Th2-cytokine profile.

MHC class II-regulated central nervous system autoaggression and T cell responses in peripheral lymphoid tissues are dissociated in myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis

We dissected the requirements for disease induction of myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis in MHC (RT1 in rat) congenic rats with overlapping MOG peptides. Immunodominance with regard to peptide-specific T cell responses was purely MHC class II dependent, varied between different MHC haplotypes, and was linked to encephalitogenicity only in RT1.B(a)/D(a) rats. Peptides derived from the MOG sequence 91-114 were able to induce overt clinical signs of disease accompanied by demyelinated CNS lesions in the RT1.B(a)/D(a) and RT1(n) haplotypes. Notably, there was no detectable T cell response against this encephalitogenic MOG sequence in the RT1(n) haplotype in peripheral lymphoid tissue. However, CNS-infiltrating lymphoid cells displayed high IFN-gamma, TNF-alpha, and IL-4 mRNA expression suggesting a localization of peptide-specific reactivated T cells in this compartment. Despite the presence of MOG-specific T and B cell responses, no disease could be induced in resistant RT1(l) and RT1(u) haplotypes. Comparison of the number of different MOG peptides binding to MHC class II molecules from the different RT1 haplotypes suggested that susceptibility to MOG-experimental autoimmune encephalomyelitis correlated with promiscuous peptide binding to RT1.B and RT1.D molecules. This may suggest possibilities for a broader repertoire of peptide-specific T cells to participate in disease induction. We demonstrate a powerful MHC class II regulation of autoaggression in which MHC class II peptide binding and peripheral T cell immunodominance fail to predict autoantigenic peptides relevant for an autoaggressive response. Instead, target organ responses may be decisive and should be further explored.

Interleukin-4 and interleukin-13 act on glomerular visceral epithelial cells

In minimal change nephrosis (MCN), proteinuria is associated with structural changes of the glomerular visceral epithelial cells (GVEC). The occurrence of MCN has been associated with 2 lymphocyte-dependent conditions. To examine a direct role for type 2 cytokines in GVEC injury, the expression of interleukin (IL)-4/IL-13 receptors by GVEC and direct effects of IL-4 and IL-13 on GVEC were studied. Reverse transcription-PCR showed that isolated human and rat glomeruli and cultured human and rat GVEC expressed mRNA for IL-4Ralpha, IL-13Ralpha1, and IL-13Ralpha2. Protein expression of [L-4Ralpha and IL-13Ralpha2 by GVEC in human kidney biopsies and by cultured human GVEC was detected by immunohistochemistry. Western blotting demonstrated phosphorylation of STAT6 in cultured GVEC upon incubation with IL-4 or IL-13. This indicated signal transduction via the heterodimeric receptor complex IL-4R2, which is composed of the IL-4Ralpha and the IL-13Ralpha1. Direct effects on GVEC function were examined in monolayer experiments. IL-4 and IL-13 dose-dependently decreased transepithelial electrical resistance of monolayers of rat GVEC to approximately 30 and 40% of baseline values, respectively. The transepithelial electrical resistance decrease was associated with a significant increase in short-circuit current, whereas no changes were observed in the transmonolayer flux of the macromolecules horseradish peroxidase (molecular weight, 44 kD) and 14C-mannitol (molecular weight, 182 Da). No changes in cell structure were observed with electron microscopy. It is concluded that by binding to specific IL-4/ IL-13 receptors, IL-4 and IL-13 can exert specific effects on GVEC function, which could be of pathogenetic relevance for glomerular injury in MCN.

Rat interleukin-4 assays

The present article describes procedures to measure rat IL-4 protein. The RT-PCR technique has been successfully and widely used to measure IL-4 mRNA, but it does not determine IL-4 protein synthesis. Assays to measure rat IL-4 protein based on its biological activity were developed using the mAb OX-81, which inhibits rat IL-4 activity. Two bioassays were attempted based on the ability of IL-4 to induce the proliferation of T cell blasts and to increase MHC class II expression on resting B cells. A second mAb against rat IL-4 was used in a sandwich ELISA to detect rat IL-4. This ELISA is satisfactory although its sensitivity is not as high as that of the bioassay. According to our experience, the bioassay based on the induction of class II MHC molecules on B cells is the technique of choice for rat IL-4 determination because it proved specific, sensitive and reproducible.