IFN-gamma modulates CD1d surface expression on intestinal epithelia

The dialogue between unconventional T cells and the microbiota

The mammalian immune system is equipped with unconventional T cells that respond to microbial molecules such as glycolipids and small-molecule metabolites, which are invisible to conventional CD4 and CD8 T cells. Unconventional T cells include invariant natural killer T (iNKT) cells and mucosa-associated invariant T (MAIT) cells, which are involved in a wide range of infectious and non-infectious diseases, such as cancer and autoimmunity. In addition, their high conservation across mammals, their restriction by non-polymorphic antigen-presenting molecules, and their immediate and robust responses make these 'innate' T cells appealing targets for the development of one-size-fits-all immunotherapies. In this review, we discuss how iNKT and MAIT cells directly and indirectly detect the presence of and respond to pathogenic and commensal microbes. We also explore the current understanding of the bidirectional relationship between the microbiota and innate T cells, and how this crosstalk shapes the immune response in disease.

Deficiency of PRKD2 triggers hyperinsulinemia and metabolic disorders

Hyperinsulinemia is the earliest symptom of insulin resistance (IR), but a causal relationship between the two remains to be established. Here we show that a protein kinase D2 (PRKD2) nonsense mutation (K410X) in two rhesus monkeys with extreme hyperinsulinemia along with IR and metabolic defects by using extreme phenotype sampling and deep sequencing analyses. This mutation reduces PRKD2 at both the mRNA and the protein levels. Taking advantage of a PRKD2-KO mouse model, we demonstrate that PRKD2 deletion triggers hyperinsulinemia which precedes to IR and metabolic disorders in the PRKD2 ablation mice. PRKD2 deficiency promotes β-cell insulin secretion by increasing the expression and activity of L-type Ca²⁺ channels and subsequently augmenting high glucose- and membrane depolarization-induced Ca²⁺ influx. Altogether, these results indicate that down-regulation of PRKD2 is involved in the pathogenesis of hyperinsulinemia which, in turn, results in IR and metabolic disorders.

Hyperinsulinemia can precede the development of insulin resistance. Here the authors identify a PKD2 mutation that leads to hyperinsulinemia and insulin resistance in Rhesus monkey and show that PKD2 deficiency promotes beta cell insulin secretion by activating L-type Ca2+ channels.

Cytokine responses and epithelial function in the intestinal mucosa

Inflammatory diseases of mucosal organs are significantly influenced by the microenvironment in which they reside. Cytokines found within this microenvironment contribute significantly to endpoint functions of the mucosa. Studies dating back to the 1990s have revealed that epithelial cells are both a source as well as a target for numerous cytokines and that such signaling can substantially influence the outcome of mucosal disease, such as inflammatory bowel disease. Here, we will review literature regarding intestinal epithelial cells as sources and responders to cytokines found in the intestinal milieu. These studies highlight the dynamic nature of these pathways and lend insight into the complexity of treating mucosal inflammation.

Activation of human T cells by CD1 and self-lipids

Over two decades ago, it was discovered that the human T-cell repertoire contains T cells that do not recognize peptide antigens in the context of MHC molecules but instead respond to lipid antigens presented by CD1 antigen-presenting molecules. The ability of T cells to 'see' lipid antigens bound to CD1 enables these lymphocytes to sense changes in the lipid composition of cells and tissues as a result of infections, inflammation, or malignancies. Although foreign lipid antigens have been shown to function as antigens for CD1-restricted T cells, many CD1-restricted T cells do not require foreign antigens for activation but instead can be activated by self-lipids presented by CD1. This review highlights recent developments in the field, including the identification of common mammalian lipids that function as autoantigens for αβ and γδ T cells, a novel mode of T-cell activation whereby CD1a itself rather than lipids serves as the autoantigen, and various mechanisms by which the activation of CD1-autoreactive T cells is regulated. As CD1 can induce T-cell effector functions in the absence of foreign antigens, multiple mechanisms are in place to regulate this self-reactivity, and stimulatory CD1-lipid complexes appear to be tightly controlled in space and time.

The role of pathway-selective insulin resistance and responsiveness in diabetic dyslipoproteinemia

PURPOSE OF REVIEW

Type 2 diabetes mellitus (T2DM) and related syndromes exhibit a deadly triad of dyslipoproteinemia, which leads to atherosclerosis, hyperglycemia, which causes microvascular disease, and hypertension. These features share a common, but unexplained, origin--namely, pathway-selective insulin resistance and responsiveness (SEIRR). Here, we review recent work on hepatic SEIRR indicating that deranged insulin signaling may have a remarkably simple molecular basis.

RECENT FINDINGS

Comprehensive examination of a set of 18 insulin targets revealed that T2DM liver in vivo exhibits a specific defect in the ability of the NAD(P)H oxidase 4 (NOX4) to inactivate protein tyrosine phosphatase gene family members after stimulation with insulin, and that impairment of this single molecule, NOX4, in cultured hepatocytes recapitulates all features of hepatic SEIRR in vivo. These features include insulin-stimulated generation of an unusual monophosphorylated form of AKT at Thr308 (pT308-AKT) with only weak phosphorylation at Ser473, impaired insulin-stimulated pathways for lowering plasma levels of lipids and glucose, but continued lipogenic pathways and robust extracellular signal-regulated kinase activation. This new study, in combination with important prior work, provides clues to several long-standing mysteries, such as how AKT might regulate lipid-lowering and glucose-lowering pathways that become insulin-resistant but also lipogenic pathways that remain insulin-responsive, as well as a potential role for NOX4 in insulin-stimulated generation of oxysterol ligands for LXR, a key lipogenic factor.

SUMMARY

These findings suggest a unified molecular explanation for fatty liver, atherogenic dyslipoproteinemia, hyperglycemia, and hence accelerated atherosclerosis and microvascular disease in T2DM, obesity, and related syndromes of positive caloric imbalance.

Functional haplotypes of Fc gamma (Fcγ) receptor (FcγRIIA and FcγRIIIB) predict risk to repeated episodes of severe malarial anemia and mortality in Kenyan children

Development of protective immunity against Plasmodium falciparum is partially mediated through binding of malaria-specific IgG to Fc gamma (γ) receptors. Variations in human FcγRIIA-H/R-131 and FcγRIIIB-NA1/NA2 affect differential binding of IgG sub-classes. Since variability in FcγR may play an important role in severe malarial anemia (SMA) pathogenesis by mediating phagocytosis of red blood cells and triggering cytokine production, the relationship between FcγRIIA-H/R131 and FcγRIIIB-NA1/NA2 haplotypes and susceptibility to SMA (Hb < 6.0 g/dL) was investigated in Kenyan children (n = 528) with acute malaria residing in a holoendemic P. falciparum transmission region. In addition, the association between carriage of the haplotypes and repeated episodes of SMA and all-cause mortality were investigated over a 3-year follow-up period. Since variability in FcγR can alter interferon (IFN)-γ production, a mediator of innate and adaptive immune responses, functional associations between the haplotypes and IFN-γ were also explored. During acute malaria, children with SMA had elevated peripheral IFN-γ levels (P = 0.006). Although multivariate logistic regression analyses (controlling for covariates) revealed no associations between the FcγR haplotypes and susceptibility to SMA during acute infection, the FcγRIIA-131H/FcγRIIIB-NA1 haplotype was associated with decreased peripheral IFN-γ (P = 0.046). Longitudinal analyses showed that carriage of the FcγRIIA-131H/FcγRIIIB-NA1 haplotype was associated with reduced risk of SMA (RR 0.65, 95% CI 0.46-0.90; P = 0.012) and all-cause mortality (P = 0.002). In contrast, carriers of the FcγRIIA-131H/FcγRIIIB-NA2 haplotype had increased susceptibility to SMA (RR 1.47, 95% CI 1.06-2.04; P = 0.020). Results here demonstrate that variation in the FcγR gene alters susceptibility to repeated episodes of SMA and mortality, as well as functional changes in IFN-γ production.

Regulation of immune responses to HPV infection and during HPV-directed immunotherapy

The recent development of vaccines prophylactic against human papillomavirus (HPV) infection has the potential to reduce the incidence of cervical cancer globally by up to 70% over the next 40 years, if universal immunization is adopted. As these prophylactic vaccines do not alter the natural history of established HPV infection, immunotherapies to treat persistent HPV infection and associated precancers would be of benefit to assist with cervical cancer control. Efforts to develop immuno-therapeutic vaccines have been hampered by the relative non-immunogenicity of HPV infection, by immunoregulatory processes in skin, and by subversion of immune response induction and immune effector functions by papillomavirus proteins. This review describes HPV-specific immune responses induced by viral proteins, their regulation by host and viral factors, and highlights some conclusions from our own recent research.

The Relation between Fructose-Induced Metabolic Syndrome and Altered Renal Haemodynamic and Excretory Function in the Rat

This paper explores the possible relationships between dietary fructose and altered neurohumoral regulation of renal haemodynamic and excretory function in this model of metabolic syndrome. Fructose consumption induces hyperinsulinemia, hypertriglyceridaemia, insulin resistance, and hypertension. The pathogenesis of fructose-induced hypertension is dubious and involves numerous pathways acting both singly and together. In addition, hyperinsulinemia and hypertension contribute significantly to progressive renal disease in fructose-fed rats. Moreover, increased activity of the renin-angiotensin and sympathetic nervous systems leading to downregulation of receptors may be responsible for the blunted vascular sensitivity to angiotensin II and catecholamines, respectively. Various approaches have been suggested to prevent the development of fructose-induced hypertension and/or metabolic alteration. In this paper, we address the role played by the renin-angiotensin and sympathetic nervous systems in the haemodynamic alterations that occur due to prolonged consumption of fructose.

Interferon-γ modulates intestinal epithelial cell function in-vitro through a TGFβ-dependent mechanism

INTRODUCTION

Interferon γ (IFNγ) has been originally identified by its anti-viral activity and has been demonstrated to act as potent modulator of the immune system with a range of target cells limited largely to immune cell populations. Although IFNγ has been shown to directly affect the barrier function of intestinal epithelial cells, only limited information is available about other functional effects of IFNγ on intestinal epithelial cells.

METHODS

The effects on intestinal epithelial cell migration were studied using a previously described in-vitro model of epithelial restitution in confluent IEC-6 cell monolayers. Intestinal epithelial cell proliferation rates were assessed in various human and rat intestinal and colon epithelial cell lines using colorimetric MTT assays. Apoptosis of IEC-6 cells exposed to IFNγ was assessed by flow cytometry. In addition, transforming growth factor β mRNA expression after IFNγ treatment of IEC-6 cells was assessed by Northern blot analysis.

RESULTS

IFNγ significantly stimulated intestinal epithelial cell migration in an in-vitro wounding model. Furthermore, IFNγ caused a significant dose-dependent inhibition of epithelial cell proliferation in non-transformed small intestinal IEC-6 cells and human colon cancer-derived HT-29 cells and no significant rates of apoptosis were detected in the exposed epithelial cells. The effect of IFNγ on epithelial cell migration and proliferation could be completely blocked by neutralizing antibodies against TGFβ indicating that these effects are mediated through a TGFβ dependent pathway. In addition, increased expression of TGFβ1 mRNA by IEC-6 cells after treatment with IFNγ supports the hypothesis that IFNγ modulates intestinal epithelial cell function through a TGFβ-dependent pathway.

CONCLUSION

These studies suggest that IFNγ produced by constituents of the mucosal immune system modulates epithelial cell functions with relevance for intestinal wound healing and may play a role in preserving the integrity of the intestinal epithelium following various forms of injuries.

Glutamatergic receptor activation in the rostral ventrolateral medulla mediates the sympathoexcitatory response to hyperinsulinemia

Hyperinsulinemia increases sympathetic nerve activity (SNA) and has been linked to cardiovascular morbidity in obesity. The rostral ventrolateral medulla (RVLM) plays a key role in the regulation of SNA and arterial blood pressure (ABP). Many sympathoexcitatory responses are mediated by glutamatergic receptor activation within the RVLM, and both the central renin-angiotensin and melanocortin systems are implicated in the sympathoexcitatory response to hyperinsulinemia. Therefore, we hypothesized that one or more of these neurotransmitters in the RVLM mediate the sympathoexcitatory response to insulin. Hyperinsulinemic-euglycemic clamps were performed in alpha-chloralose anesthetized, male Sprague-Dawley rats by infusion of insulin (3.75 mU/kg per minute, IV) and 50% dextrose solution for 120 minutes. Physiological increases in plasma insulin elevated lumbar SNA, with no change in renal SNA, ABP, or blood glucose. Microinjection of the ionotropic glutamate receptor antagonist kynurenic acid into the RVLM significantly reduced lumbar SNA and ABP. Selective blockade of NMDA but not non-NMDA glutamate receptors resulted in similar reductions of lumbar SNA. In marked contrast, microinjection of the angiotensin II type 1 receptor antagonist losartan or the melanocortin 3/4 antagonist SHU9119 had no effect on lumbar SNA or ABP. Western blot analysis showed that insulin receptor expression is significantly lower in the RVLM than the hypothalamus, and direct microinjection of insulin into the RVLM did not significantly increase lumbar SNA. These findings suggest that hyperinsulinemia increases lumbar SNA by activation of a glutamatergic NMDA-dependent projection to the RVLM.

Invariant NKT cells in hyperplastic skin induce a local immune suppressive environment by IFN-gamma production

NKT cells can promote or inhibit adaptive immune responses. Cutaneous immunity is tightly regulated by cooperation between innate and adaptive immune processes, but the role of NKT cells in regulating cutaneous immunity is largely unknown. In this study, we show, in a mouse model, that skin-infiltrating CD1d-restricted NKT cells in HPV16-E7 transgenic hyperplastic skin produce IFN-gamma, which can prevent rejection of HPV16-E7-expressing skin grafts. Suppression of graft rejection is associated with the accumulation of CD1d(hi)-expressing CD11c(+)F4/80(hi) myeloid cells in hyperplastic skin. Blockade of CD1d, removal of NKT cells, or local inhibition of IFN-gamma signaling is sufficient to restore immune-mediated graft rejection. Thus, inhibition of NKT cell recruitment or function may enable effective immunity against tumor and viral Ags expressed in epithelial cells.

A central role for transcription factor C/EBP-beta in regulating CD1d gene expression in human keratinocytes

CD1d is a nonclassical Ag-presenting molecule that presents glycolipid Ags to NKT cells that are involved in immune defense and tumor rejection. It also plays a role in immunoregulatory functions in the epidermis. The mechanisms controlling the expression of CD1d are not well understood. Therefore, we cloned the CD1d gene promoter and characterized its activities in primary human keratinocytes and other cell lines of epithelial origin. We found that a CCAAT box in the CD1d promoter is required for its expression in keratinocytes. We show here that transcription factor C/EBP-beta binds to the CCAAT box in the CD1d promoter in vitro and in vivo. Consistent with these observations, deletion of the gene encoding for C/EBP-beta caused a loss of CD1d expression. The in vivo regulation of CD1d has significant implications for the pathologic mechanisms of certain immunologic skin diseases in which NKT cells play a role, such as allergic contact dermatitis and psoriasis. Together, these data show a central role for C/EBP-beta in regulating CD1d transcription.

Enrichment of human CD4+ V(alpha)24/Vbeta11 invariant NKT cells in intrahepatic malignant tumors

Invariant NKT cells (iNKT cells) recognize glycolipid Ags via an invariant TCR alpha-chain and play a central role in various immune responses. Although human CD4(+) and CD4(-) iNKT cell subsets both produce Th1 cytokines, the CD4(+) subset displays an enhanced ability to secrete Th2 cytokines and shows regulatory activity. We performed an ex vivo analysis of blood, liver, and tumor iNKT cells from patients with hepatocellular carcinoma and metastases from uveal melanoma or colon carcinoma. Frequencies of Valpha24/Vbeta11 iNKT cells were increased in tumors, especially in patients with hepatocellular carcinoma. The proportions of CD4(+), double negative, and CD8alpha(+) iNKT cell subsets in the blood of patients were similar to those of healthy donors. However, we consistently found that the proportion of CD4(+) iNKT cells increased gradually from blood to liver to tumor. Furthermore, CD4(+) iNKT cell clones generated from healthy donors were functionally distinct from their CD4(-) counterparts, exhibiting higher Th2 cytokine production and lower cytolytic activity. Thus, in the tumor microenvironment the iNKT cell repertoire is modified by the enrichment of CD4(+) iNKT cells, a subset able to generate Th2 cytokines that can inhibit the expansion of tumor Ag-specific CD8(+) T cells. Because CD4(+) iNKT cells appear inefficient in tumor defense and may even favor tumor growth and recurrence, novel iNKT-targeted therapies should restore CD4(-) iNKT cells at the tumor site and specifically induce Th1 cytokine production from all iNKT cell subsets.

Activation of the JAK/STAT-1 signaling pathway by IFN-gamma can down-regulate functional expression of the MHC class I-related neonatal Fc receptor for IgG

Expression of many MHC genes is enhanced at the transcriptional or posttranscriptional level following exposure to the cytokine IFN-gamma. However, in this study we found that IFN-gamma down-regulated the constitutive expression of the neonatal Fc receptor (FcRn), an MHC class I-related molecule that functions to transport maternal IgG and protect IgG and albumin from degradation. Epithelial cell, macrophage-like THP-1 cell, and freshly isolated human PBMC exposure to IFN-gamma resulted in a significant decrease of FcRn expression as assessed by real-time RT-PCR and Western blotting. The down-regulation of FcRn was not caused by apoptosis or the instability of FcRn mRNA. Chromatin immunoprecipitation and gel mobility shift assays showed that STAT-1 bound to an IFN-gamma activation site in the human FcRn promoter region. Luciferase expression from an FcRn promoter-luciferase reporter gene construct was not altered in JAK1- and STAT-1-deficient cells following exposure to IFN-gamma, whereas expression of JAK1 or STAT-1 protein restored the IFN-gamma inhibitory effect on luciferase activity. The repressive effect of IFN-gamma on the FcRn promoter was selectively reversed or blocked by mutations of the core nucleotides in the IFN-gamma activation site sequence and by overexpression of the STAT-1 inhibitor PIAS1 or the dominant negative phospho-STAT-1 mutations at Tyr-701 and/or Ser-727 residues. Furthermore, STAT-1 might down-regulate FcRn transcription through sequestering the transcriptional coactivator CREB binding protein/p300. Functionally, IFN-gamma stimulation dampened bidirectional transport of IgG across a polarized Calu-3 lung epithelial monolayer. Taken together, our results indicate that the JAK/STAT-1 signaling pathway was necessary and sufficient to mediate the down-regulation of FcRn gene expression by IFN-gamma.

Expression of CD1d and ligand-induced cytokine production are tissue specific in mucosal epithelia of the human lower reproductive tract

Mucosal epithelia of the human lower reproductive tract (vagina, cervix, and penile urethra) are exposed to sexually transmitted microbes, including Chlamydia trachomatis. The in vivo susceptibility of each tissue type to infection with C. trachomatis is quite distinct. CD1d is expressed on the surface of antigen-presenting cells, including mucosal epithelial cells, and interacts specifically with invariant NKT cells. Invariant NKT cells play a role in both innate and adaptive immune responses to microbes. Here we assessed CD1d expression in normal reproductive tissues by using immunohistochemistry. Immortalized epithelial cell lines from the human lower reproductive tract (vagina, endocervix, and penile urethra) were examined for CD1d expression and for ligand-induced cytokine production induced by CD1d cross-linking. CD1d expression in normal tissue was strong in the vagina but weak in the endocervix and penile urethra. Gamma interferon exposure induced CD1d transcription in all of the cell types studied, with the strongest induction in vaginal cells. Flow cytometry revealed cell surface expression of CD1d in vaginal and penile urethral epithelial cells but not in endocervical cells. Ligation of surface-expressed CD1d by monoclonal antibody cross-linking promoted interleukin-12 (IL-12) and IL-15, but not IL-10, production in vaginal and penile urethral cells. No induction was demonstrated in endocervical cells. CD1d-mediated cytokine production in penile urethral cells was abrogated by C. trachomatis infection. Basal deficiency in CD1d-mediated immune responsiveness may result in susceptibility to sexually transmitted agents. Decreased CD1d-mediated signaling may help C. trachomatis evade detection by innate immune cells.

Roles of CD1d-restricted NKT cells in the intestine

Natural killer T (NKT) cells are a subset of lymphocytes that express cell surface molecules of both conventional T cells and natural killer cells and share the features of both innate and adaptive immune cells. NKT cells have been proposed to make both protective and pathogenic contributions to inflammatory bowel diseases (IBD). On the one hand, recent studies have shown that these cells are involved in the maintenance of mucosal homeostasis. On the other, NKT cells were shown to play a pathogenic role in human ulcerative colitis. Similar contrasting data have been generated in murine models of IBD. Whether the apparent differences in NKT response patterns depend on variations in NKT antigens and/or on the presence of specific subsets of mucosal NKT cells remains to be elucidated. In this article we review the current literature on intestinal NKT cells and their roles in IBD pathogenesis. Specifically, the nomenclature, NKT antigens, and immune mechanisms of NKT cells within the intestinal mucosa are discussed.

CD1 expression on antigen-presenting cells

CD1 proteins present self and microbial glycolipids to CD 1-restricted T cells, or in the case of CD1d, to NKT cells. The CD1 family in humans consists of group I proteins CDla, CDlb, CDlc, and CDle and the group II protein CDld. Rodents express only CDld, but as CD1d is broadly expressed and traffics to all endosomal compartments, this single CD1 family member is thereby able to acquire antigens in many subcellular compartments. A complete understanding of the CD 1 family requires an appreciation of which cells express CD1 and how CD1 contributes to the unique function of each cell type. While group I CD 1 expression is limited to thymocytes and professional APCs, CD1d has a wider tissue distribution and can be found on many nonhematopoietic cells. The expression and regulation of CD1 are presented here with particular emphasis on the function of CD1 in thymocytes, B cells, monocytes and macrophages, dendritic cells (DCs), and intestinal epithelial cells (IECs). Altered expression of CD 1 in cancer, autoimmunity, and infectious disease is well documented, and the implication of CD 1 expression in these diseases is discussed.

Expression of nonclassical class I molecules by intestinal epithelial cells

It is well recognized that the nature of the immune response is different in the intestinal tract than in peripheral lymphoid organs. The immunologic tone of the gut-associated lymphoid tissue is one of suppression rather than active immunity, distinguishing pathogens from normal flora. Failure to control mucosal immune responses may lead to inflammatory diseases such as Crohn's disease (CD) and ulcerative colitis (UC) and celiac disease. It has been suggested that this normally immunosuppressed state may relate to unique antigen-presenting cells and unique T-cell populations. The intestinal epithelial cell (IEC) has been proposed to act as a nonprofessional antigen-presenting cell (APC). Previous studies have suggested that antigens presented by IECs result in the activation a CD8(+) regulatory T-cell subset in a nonclassical MHC I molecule restricted manner. We therefore analyzed the expression of nonclassical MHC I molecules by normal IECs and compared this to those expressed by inflammatory bowel disease (IBD) IECs. Normal surface IEC from the colon and, to a much lesser extent, the small bowel express nonclassical MHC I molecules on their surface. In contrast, mRNA is expressed in all intestinal epithelial cells. Surface IEC express CD1d, MICA/B, and HLA-E protein. In contrast, crypt IECs express less or no nonclassical MHC I molecules but do express mRNA for these molecules. Furthermore, the regulation of expression of distinct nonclassical class I molecules is different depending on the molecule analyzed. Interestingly, IECs derived from patients with UC fail to express any nonclassical MHC I molecules (protein and HLA-E mRNA). IECs from CD patients express HLA-E and MICA/B comparable to that seen in normal controls but fail to express CD1d. Thus, in UC there may be a failure to activate any nonclassical MHC I molecule restricted regulatory T cells that may result in unopposed active inflammatory responses. In CD only the CD1d-regulated T cells would be affected.

Defective renal dopamine D1 receptor function contributes to hyperinsulinemia-mediated hypertension

Hyperinsulinemia is reported to play a role in hypertension, as abnormalities in blood pressure regulation and sodium handling exist in diabetes mellitus. Kidney dopamine promotes sodium excretion via the activation of renal D1 receptors. Because there is a close relationship between renal D1 receptor function and sodium excretion, it is hypothesized that a defect in this mechanism may contribute to decreased sodium excretion and hypertension during hyperinsulinemia. Renal D1 receptor function was studied in insulin-induced hypertension in male Sprague Dawley rats. Insulin pellets were implanted subcutaneously for controlled insulin release for three weeks; sham rats served as a control. Compared to control rats, insulin pellets increased plasma insulin levels by eight fold and decreased blood glucose by 40%. Insulin also caused a 22 mmHg increase in mean arterial blood pressure compared to control animals. The intravenous infusion of SKF-38393, a D1 receptor agonist, increased sodium excretion in control rats, but SKF-38393 failed to produce natriuresis in hyperinsulinemic animals. Renal proximal tubules from hyperinsulinemic rats had a reduced D1 receptor number, defective receptor-G protein coupling, and blunted SKF-38393 induced Na, K-ATPase inhibition. Insulin seems to reduce D1 receptor expression and coupling to the G-protein, leading to a reduced D1 receptor-mediated Na, K-ATPase inhibition, and a diminished natriuretic response to SKF-38393. These phenomena could account for sodium retention and hypertension associated with hyperinsulinemia.

The oligopeptide transporter hPepT1: gateway to the innate immune response

Bacterial products that are normally present in the lumen of the colon, such as N-formylated peptides and muramyl-dipeptide, are important for inducing the development of mucosal inflammation. The intestinal dipeptide transporter, hPepT1, which is expressed in inflamed but not in noninflamed colonic epithelial cells, mediates the transport of these bacterial products into the cytosol of colonic epithelial cells. The small bacterial peptides subsequently induce an inflammatory response, including the induction of MHC class I molecules expression and cytokines secretion, via the activation of nucleotide-binding site and leucine-rich repeat (NBS-LRR) proteins, for example NOD2, and activation of NF-kappaB. Subsequent secretion of chemoattractants by colonic epithelial cells induces the movement of neutrophils through the underlying matrix, as well as across the epithelium. These bacterial products can also reach the lamina propria through the paracellular pathway and across the basolateral membrane of epithelial cells. As a consequence, small formylated peptides can interact directly with immune cells through specific membrane receptors. Since immune cells, including macrophages, also express hPepT1, they can transport small bacterial peptides into the cytosol where these may interact with the NBS-LRR family of intracellular receptors. As in intestinal epithelial cells, the presence of these small bacterial peptides in immune cells may trigger immune response activation.

Alteration of intestinal epithelial function by intraepithelial lymphocyte homing

BACKGROUND

Intimate cross-talk may take place between intestinal epithelial cells and intraepithelial lymphocytes (IEL). The purpose of this study was to analyze the influence of lymphocyte migration into the epithelium on epithelial function, using an in vitro "IEL homing" model.

METHODS

Molecular expression on epithelial cells was analyzed by flow cytometry. The barrier function of the epithelial monolayer was assessed by transepithelial electrical resistance. Cytokine production was measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

(1) IEL homing into the epithelia induced significant phenotypic changes in epithelial cells; upregulation of MHC class I, and II, intercellular adhesion molecule (ICAM)-1, and CD44. IEL-derived interferon-gamma (IFN-gamma) could partially account for this alteration, as a neutralizing antibody (Ab) against IFN-gamma inhibited the upregulation of these molecules, except for CD44. (2) A marked fall in transepithelial electrical resistance was observed 4 h after IEL homing started, and Ab against IFN-gamma slightly inhibited this fall in resistance. (3) The production of interleukin (IL)-8 and IFN-gamma inducible protein-10 (IP-10), but not transforming growth factor (TGF)-beta1 or tumor necrosis factor (TNF)-alpha, in the epithelial monolayer was markedly induced after IEL homing in a basolaterally polarized fashion. IEL-conditioned media also induced the production of these cytokines in epithelial cells, thus suggesting that IEL-derived soluble factor(s) induce epithelial chemokine production.

CONCLUSIONS

Under inflammatory conditions, IEL obviously interact with epithelial cells and upregulate adhesion molecules, alter barrier function, and enhance chemokine production. Because such alterations may increase epithelial permeability to luminal antigens or accelerate the migration of other inflammatory cells, our results suggest that IEL have a critical role in mucosal immunity.

Evidence for a link between sphingolipid metabolism and expression of CD1d and MHC-class II: monocytes from Gaucher disease patients as a model

Gaucher disease (GD) is an autosomal recessive inherited defect of the lysosomal enzyme glucocerebrosidase (GluCerase) that leads to glucosylceramide (GluCer) accumulation. We previously demonstrated the existence of imbalances in certain lymphocyte populations in GD patients. We now show that GluCerase-deficient monocytes from GD patients or monocytes from healthy subjects treated with conduritol-B-epoxide (CBE), an irreversible inhibitor of GluCerase activity, display high levels of surface expression of the lipid-binding molecule CD1d. GluCerase-deficient monocytes from GD patients also showed increased surface expression of major histocompatibility complex (MHC)-class II, but not of other lysosomal trafficking molecules, such as CD63 and MHC-class I. However, CD1d and MHC-class II mRNA levels were not increased. GluCerase-deficient monocytes from GD patients undergoing enzyme replacement therapy also exhibited increased levels of CD1d and MHC-class II and imbalances in the percentage of CD4+, CD8+, and Valpha24+ T cells. Interestingly, follow-up studies revealed that enzyme replacement therapy induced a decrease in MHC-class II expression and partial correction of the CD4+ T cell imbalances. These results reveal a new link between sphingolipid accumulation in monocytes and the expression of certain MHC molecules that may result in imbalances of regulatory T cell subsets. These immunological anomalies may contribute to the clinical heterogeneity in GD patients.

Natural Killer T Cells in Mucosal Homeostasis

The mucosal-associated lymphoid tissues (MALT), including the gut-associated lymphoid tissues, are a tightly regulated environment. In fact, it might be stated that on the basis of studies from animal models of inflammatory bowel disease (IBD), the major means of peripheral regulation of immune responses in the intestine is not necessarily from processes such as deletion or anergy, but more likely from the controls imposed upon responses due to the activities of a variety of regulatory subsets of cells. One type of regulatory cellular subset that has recently gained attention is the subset of T cells that are associated with CD1d-restricted responses. Recently, CD1d-restricted T cells have been increasingly appreciated to play a significant role in mucosal tissues of the intestine and lung, for example. Insights from these studies have clearly elevated these cells to particular importance in the regulation of a variety of infectious and inflammatory conditions, such as those associated with idiopathic IBD. In this review, we focus on recent observations on the characteristics of CD1d-restricted pathways in mucosal compartments, after a brief introduction into the biology of CD1d and CD1d-restricted T cells.

Human CD1D gene has TATA boxless dual promoters: an SP1-binding element determines the function of the proximal promoter

CD1d presents lipid Ags to a specific population of NK T cells, which are involved in the host immune defense, suppression of autoimmunity, and the rejection of tumor cells. The transcriptional control mechanism that determines the regulation and the tissue distribution of CD1d remains largely unknown. After investigating 3.7 kb 5' upstream of the coding region, we found that human gene encoding CD1d molecule (CD1D) has TATA boxless dual promoters with multiple transcription initiation sites. The proximal promoter is located within the region of -106 to +24, and the distal promoter is located within the region of -665 to -202 with the A of the translational start codon defined as +1. The longest 5'-untranslated region derived from 5'-RACE and apparently generated by the distal promoter has 272 bp in length covering the genomic sequence of the proximal promoter. The region covering the proximal promoter gave a much higher luciferase activity in Jurkat cells than in K562 cells, whereas it was in reverse for the region covering the distal promoter, indicating a cell type sp. act. of the two promoters. Transcription factor SP1 plays a crucial role in the function of the proximal promoter. The analysis of the CD1D promoter region indicates that IFN-gamma, NF-IL-6, and T cell factor 1/lymphoid enhancer-binding factor 1 are most likely involved in the regulation of CD1d expression. The illustration of the dual CD1D gene promoters will help to reveal the regulatory factors that control CD1d expression and its tissue distribution for a better understanding of the cross-regulation between CD1d and NK T cells.

CD1: antigen presentation and T cell function

This review summarizes the major features of CD1 genes and proteins, the patterns of intracellular trafficking of CD1 molecules, and how they sample different intracellular compartments for self- and foreign lipids. We describe how lipid antigens bind to CD1 molecules with their alkyl chains buried in hydrophobic pockets and expose their polar lipid headgroup whose fine structure is recognized by the TCR of CD1-restricted T cells. CD1-restricted T cells carry out effector, helper, and adjuvant-like functions and interact with other cell types including macrophages, dendritic cells, NK cells, T cells, and B cells, thereby contributing to both innate and adaptive immune responses. Insights gained from mice and humans now delineate the extensive range of diseases in which CD1-restricted T cells play important roles and reveal differences in the role of CD1a, CD1b, and CD1c in contrast to CD1d. Invariant TCR alpha chains, self-lipid reactivity, and rapid effector responses empower a subset of CD1d-restricted T cells (NKT cells) to have unique effector functions without counterpart among MHC-restricted T cells. This review describes the function of CD1-restricted T cells in antimicrobial responses, antitumor immunity, and in regulating the balance between tolerance and autoimmunity.

Identification of three genomic haplotypes 5' to the human CD1D gene and their distribution in four ethnic groups

CD1d presents lipid antigen to a conserved population of natural killer (NK) T cells, which participate in host immune defense, tumor cell rejection and suppression of autoimmunity. The levels of human CD1d expression vary significantly between individuals. To understand such variation, we sequenced the region up to 1.7 kb 5' upstream of the translation start site and partially through exon 2 in 44 white Americans. We also studied two tagged single nucleotide polymorphisms (SNP) in 112 white Americans, 60 African-Americans, 88 Europeans, and 84 Chinese people from the region. Six SNP present in the region (-836C-->T, -773C-->T, -764C-->G, -713A-->T, -365A-->G and +363A-->G) were found to be in a complete linkage disequilibrium and comprised three haplotypes. Haplotype 1 had -836C, -773C, -764C, -713A, -365A and +363A. Haplotype 2 had -836C, -773T, -764C, -713A, -365A and +363A. Haplotype 3 had -836T, -773C, -764G, -713T, -365G and +363G. -773C-->T and -764C-->G can serve as the tagged SNP to differentiate the three haplotypes. The frequency of haplotype 1 was significantly higher in African Americans than in the other three ethnic groups, whereas the frequency of haplotype 3 was significantly higher in the Chinese people than those in the other three groups. The finding of the three haplotypes provides a genetic marker for CD1d and facilitates the study of the functional role of the genetic variations in human CD1d expression and regulation.

Interferon-gamma increases hPepT1-mediated uptake of di-tripeptides including the bacterial tripeptide fMLP in polarized intestinal epithelia

Interferon-gamma causes a global phenotypic switch in intestinal epithelial function, in which enterocytes become immune accessory cells. The phenotypic switch is characterized by a down-regulation of membrane transporters and up-regulation of immune accessory molecules in intestinal epithelial cells. However, the effect of interferon-gamma on the intestinal epithelia di-tripeptide hPepT1 transporter has not been investigated. In this study we demonstrate that 1) interferon-gamma increases di-tripeptide uptake in dose- and time-dependent manner in model intestinal epithelia (Caco-2 BBE cell monolayers), 2) the increase in di-tripeptides induced by interferon-gamma is hPepT1 mediated, 3) interferon-gamma does not affect the hPept1 expression at the mRNA and protein levels 4) interferon-gamma increases the intracellular pH and consequently enhances the H+-electrochemical gradient across apical plasma membrane in model intestinal epithelia (Caco2-BBE monolayers). We suggest that interferon-gamma could increase the hPepT1 mediated di-tripeptides uptake in inflamed epithelial cells. Under these conditions, interferon-gamma will increase the intracellular amount of such diverse prokaryotic and eucaryotic small di-tripeptides in inflamed epithelial cells. The intracellular accumulation of such di-tripeptides may be important in enterocytes becoming immune accessory cells.

Insulin-stimulated hydrogen peroxide increases guanylate cyclase activity in vascular smooth muscle

Insulin resistance is associated with vascular disease. Physiological concentrations of insulin inhibit cultured vascular smooth muscle cell (VSMC) contraction and migration by increasing nitric oxide (NO)-stimulated cGMP accumulation. The failure to do so in insulin-resistant states may aggravate vascular disease. We sought to determine the mechanism of insulin's increase in cGMP accumulation. Isobutylmethylxanthine, an inhibitor of phosphodiesterase activity, inhibited the decline in cGMP levels measured by immunoassay in cGMP-loaded cultured rat aortic VSMCs, but 1 nmol insulin did not. Thus, insulin's increase in cGMP accumulation is due to stimulated production, not inhibited hydrolysis and/or efflux. Insulin, which increases the NADH/NAD+ ratio in these cells, stimulated superoxide anion (O2-) accumulation measured by lucigenin luminescence to 256+/-25% (P<0.05) by a process that was blocked by the NADH oxidase inhibitor diphenyliodonium (DPI) and enhanced by the superoxide dismutase inhibitor diethyldithiocarbonate (DETCA). Insulin also stimulated hydrogen peroxide (H2O2) accumulation measured by horseradish peroxidase/luminol luminescence to 221+/-22% (P<0.05) by a DETCA-sensitive mechanism. H2O2 (100 micromol/L) in the absence of insulin increased NO-stimulated cGMP accumulation to 151+/-11% (P<0.05). Insulin alone increased NO-stimulated cGMP accumulation to 183+/-17% (P<0.05), and this was blocked by either DPI or DETCA. We conclude that insulin increases NADH oxidase-derived O2- production in cultured rat VSMCs. This did not cause the expected scavenging of NO resulting in the reduction of NO-stimulated guanylate cyclase activity, but enough O2- was metabolized to H2O2 to increase overall NO-stimulated cGMP production.

Intestinal heat shock protein 110 regulates expression of CD1d on intestinal epithelial cells

CD1d is expressed on the surface of professional and nonprofessional APCs, including intestinal epithelial cells (IECs), for a role in the presentation of glycolipid-based antigens to subsets of T cells. The mechanisms that regulate CD1d expression in any cell type are unknown. To investigate the possibility that expression of CD1d is influenced by exogenous factors present within the intestinal lumen, CD1d expression was analyzed in several IEC lines after culturing in the presence of lumenal contents (LC) of the normal human intestine. Exposure of the colon-derived cell lines T84, HT-29, and Caco-2 to soluble LC resulted in a marked induction of CD1d expression as determined by RT-PCR, confocal microscopy, cell surface ELISA, and Western blot analysis. Similarly, exposure of human IECs to LC isolated from mice bred in both specific pathogen-free and germfree conditions also resulted in the induction of CD1d expression, with the maximum CD1d-inducing activity observed in the small intestine. Biochemical and biophysical characterization of the human CD1d-inducing activity identified heat shock protein 110 (Hsp110) as a major functional component of the LC that contributes to CD1d surface regulation, and immunolocalization studies revealed Hsp110 expression in subsets of human IECs in vivo. These data support the presence of a novel autocrine pathway of CD1d regulation by Hsp110.

Oxidative stress in Dahl salt-sensitive hypertension

The role of oxidative stress in the long-term regulation of arterial pressure, renal hemodynamics, and renal damage was studied in Dahl salt-sensitive rats. Twenty-eight Dahl S/Rapp strain rats, equipped with indwelling arterial and venous catheters, were subjected to a 3-week intravenous infusion of either low Na (0.9 mmol/d) or high Na (20.6 mmol/d) or the superoxide dismutase mimetic, 4-hydroxyl-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol), at 125 micromol x kg(-1) x h(-1) plus low Na or high Na. After 21 days, mean arterial pressure was 140+/-3 mm Hg in the high-Na group, 118+/-1 mm Hg (P<0.05) in the high-Na/Tempol group, and unchanged in the low-Na/Tempol and low-Na groups. Tempol did not change renal blood flow, glomerular filtration rate, or glomerular cross-sectional area in rats subjected to the high-Na intake but did decrease urinary protein excretion, the percentage of sclerotic glomeruli, and the kidney weight to body weight ratio. In 15 additional Dahl S rats subjected to high or low Na intake for 3 weeks, renal cortical and medullary O2*- release increased significantly in the high-Na group when compared with the low-Na group. Tempol decreased both renal cortical and medullary O2*- release in the high- and low-Na rats, but the decrease in O2*- release was greater in high-Na rats. The data suggest that oxidative stress contributes to Dahl salt-sensitive hypertension and the accompanying renal damage.

Insulin-stimulated cyclic guanosine monophosphate inhibits vascular smooth muscle cell migration by inhibiting Ca/calmodulin-dependent protein kinase II

BACKGROUND

Insulin resistance is associated with vascular disease. Physiological concentrations of insulin inhibit cultured vascular smooth muscle cell (VSMC) migration in the presence of nitric oxide, and the failure to do so in insulin-resistant states may aggravate vascular disease. We sought to determine the molecular mechanisms by which insulin inhibits VSMC migration.

METHODS AND RESULTS

Insulin at 1 nmol/L stimulated cGMP production in cultured rat VSMCs that were induced to express inducible nitric oxide synthase (iNOS). VSMC migration was measured in a wound-closure assay, and the platelet-derived growth factor-AB (PDGF-AB)-stimulated component of VSMC migration after wounding was inhibited by insulin, 8-Br-cGMP, and 1-[N-0-bis(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine (KN-62), a selective inhibitor of calcium/calmodulin-dependent protein kinase II (CaM kinase II). Wounding alone or incubating cells with only PDGF-AB stimulated CaM kinase II activity in an insulin- and 8-Br-cGMP-inhibitable manner. Transfecting VSMCs with a constitutively active CaM kinase II mutant blocked the inhibition by insulin of both wound-induced and wound plus PDGF-AB-induced VSMC migration. High intracellular Ca2+ ([Ca]i)-stimulated CaM kinase II activity was inhibited by 8-Br-cGMP by an okadaic acid-sensitive mechanism.

CONCLUSIONS

We conclude that in cultured rat VSMCs expressing iNOS, insulin, via stimulation of cGMP production, inhibits both wound alone-induced and the PDGF-AB-stimulated component of VSMC migration by inhibiting CaM kinase II activity. cGMP inhibits CaM kinase II at a post-[Ca]i step by a protein phosphatase-dependent mechanism.

Nitric oxide opposes glucose-induced hypertension by suppressing sympathetic activity

We have reported that glucose infusion in L-NAME-treated rats increased arterial pressure more than the additive responses to glucose and L-NAME alone. This suggested that nitric oxide synthesis inhibition potentiated the hypertensive response to chronic glucose infusion, and the heart rate data suggested an important role for the sympathetic nervous system. This study tested the role of the sympathetic nervous system by infusing glucose for 7 days in 4 groups of rats: L-NAME (L), L-NAME plus alpha- and beta-adrenergic receptor blockade (LB), vehicle, or vehicle plus adrenergic receptor blockade (blockers). Mean arterial pressure (MAP, 24 hours per day) increased significantly in both the vehicle and blockers groups, confirming our previous reports. Likewise, MAP increased significantly more during glucose infusion in the L rats, from 120+/-3 mm Hg to 158+/-4 mm Hg by day 7, which was >3 times the increase in the vehicle rats. Heart rate also increased significantly in the L rats, from 391+/-4 to 426+/-8 bpm, and that increase was prevented completely in the LB rats. However, although the increase in MAP in the LB rats was significantly less than in the L rats, the hypertension was not prevented completely. The explanation for that partial inhibition is not clear, but the overall effectiveness of adrenergic receptor blockade to attenuate the potentiated hypertensive and tachycardic responses to glucose infusion in the L-NAME-treated rats versus the normal rats suggests that nitric oxide may help protect against hypertension during glucose infusion through suppression of sympathetic activity.

Interferon-gamma-secreting T cells localize to the epithelium in coeliac disease

Increased levels of interferon-gamma (IFN-gamma) transcripts have previously been found in duodenal biopsy specimens from patients with untreated coeliac disease (CD). Such samples and duodenal control mucosa were therefore studied to locate and phenotype cells spontaneously secreting IFN-gamma. Specimens were collected from consecutively recruited patients with untreated (seven), treated (four) or refractory (three) CD and from five histologically normal controls. Morphological and immunohistochemical examinations were performed, and epithelial and lamina propria cell suspensions were prepared from parallel samples. Unstimulated viable cells secreting IFN-gamma were identified and phenotyped with a new fluorescence-activated cell sorter-based assay, and IFN-gamma messenger RNA (mRNA) was analysed in snap-frozen aliquots of the same suspensions. Untreated CD cases had the highest fraction of IFN-gamma+ cells in the epithelial compartment (median 2.6%, range 1.6-6.2%) and, less strikingly, in the lamina propria compartment (1.6%, range 0.3-3.6%), followed by refractory (1.4%, 1.0-1.9%; and 0.3%, 0.0-1.2%) and treated (0.8%, 0.5-0.9%; and 0.7%, 0.2-1.1%) disease and finally the controls (0.5%, 0.3-0.9%; and 0.2%, 0.1-0.7%). IFN-gamma mRNA data supported these findings. IFN-gamma+ intraepithelial lymphocytes were mostly CD3+ and CD8+, whereas many positive lamina propria cells were CD8-. We conclude that isolated T cells spontaneously secreting IFN-gamma localize preferentially in the epithelium of patients with classical and refractory CD.

Expression profiling of B cell chronic lymphocytic leukemia suggests deficient CD1-mediated immunity, polarized cytokine response, altered adhesion and increased intracellular protein transport and processing of leukemic cells

We used oligonucleotide microarrays to profile the expression of chronic lymphocytic leukemia (CLL) B cells from eight patients compared with CD5-expressing normal B cells from four donors and with pooled normal circulating B cells. Of 6790 genes examined, we identified 87 genes that were differentially expressed at least two-fold between CLL and the normal B cells. CLL cells significantly down-regulated transcripts from CD1c and CD1d genes, which encode proteins known to present lipid antigen and mediate innate and adaptive immunity. The expression pattern was also consistent with reduced signaling by interferon gamma but increased response to interleukin 4 in leukemic cells. CLL cells increased the expression of several collagen-associated extracellular matrix and adhesion molecules, up-regulated many genes involved in intracellular protein transport and processing, while downregulating genes involved in proliferation and metabolism. Based on the expression pattern, we propose that CLL-B cells prolong their survival through increased interaction with survival factors such as IL-4, and through various mechanisms of evading the immune response, such as turning off the expression of CD1c and CD1d, reducing immunogenic response to interferon gamma, inactivating T cell in B-T interaction and increasing the expression of immunoglobulin receptors which neutralize antibody-dependent cell-mediated cytotoxicity.

Colonic epithelial hPepT1 expression occurs in inflammatory bowel disease: transport of bacterial peptides influences expression of MHC class 1 molecules

BACKGROUND & AIMS

hPepT1 is an intestinal epithelial apical membrane transporter responsible for uptake of di/tripeptides (including bacterial derived proinflammatory n-formyl peptides). hPepT1 expression normally has a strict axial gradient-highest in the proximal small intestine with no expression in the colon.

METHODS

Small intestinal-like cells (Caco2-BBE), and colonic-like cells (HT29-Cl.19A), and colonic mucosa from diseased and control patients were used in the present study.

RESULTS

hPepT1 expression occurs aberrantly in the colon with chronic ulcerative colitis (6 patients) and Crohn's disease (4 patients), but not in normal colon (4 patients) or colon with microscopic colitis (4 patients). To model expression of hPepT1 by colonic-like cells in inflamed states, we stably transfected HT29-Cl.19A cells with a modified hPepT1 tagged on the N-terminus with green fluorescence protein. Analysis of transfected cells revealed that: GFP-hPepT1 protein, like the natural protein, is targeted to the apical plasma membrane. In addition, the tagged protein retains the capability of di/tripeptide absorption, and the expression of the tagged protein by HT29-Cl.19A cells permits absorption of N-formyl-methionyl-leucyl-phenylalanine (fMLP), as occurs in hPepT1 expressing Caco2-BBE cells. fMLP uptake by colonic cells expressing GFP-hPepT1 specifically enhances major histocompatibility complex class I surface expression.

CONCLUSIONS

These data collectively indicate that, in some states of chronic inflammation, hPepT1 may be anomolously expressed in the colon. Further, transport of fMLP by hPepT1 potentially stimulates expression of key accessory immune molecule, MHC-1.

Human CD1d functions as a transplantation antigen and a restriction element in mice

To study the potential functions of human CD1d (hCD1d), we developed transgenic (Tg) mice that ectopically express hCD1d under the control of H-2K(b) promoter. High levels of hCD1d expression were detected in all Tg tissues tested. Skin grafts from the K(b)/hCD1d Tg mice were rapidly rejected by MHC-matched non-Tg recipient mice, suggesting that hCD1d can act as transplantation Ags. Furthermore, we were able to elicit hCD1d-restricted CD8(+) CTLs from mice immunized with K(b)/hCD1d Tg splenocytes. These CTLs express TCR rearrangements that are distinct from invariant TCR of NK T cells, and secrete significant amounts of IFN-gamma upon Ag stimulation. Analysis with various hCD1d-expressing targets and use of Ag presentation inhibitors indicated the recognition of hCD1d by CTLs did not involve species or tissue-specific ligands nor require the processing pathways of endosomes or proteasomes. Additionally, the reactivity of hCD1d-specific CTLs was not affected by acid stripping followed by brefeldin A treatment, suggesting that CTLs may recognize a ligand/hCD1d complex that is resistant to acid denaturation, or empty hCD1d molecules. Our results show that hCD1d can function as an alloantigen for CD8(+) CTLs. The hCD1d Tg mice provide a versatile model for the study of hCD1d-restricted cytolytic responses to microbial Ags.

Long-term glucose infusion increases arterial pressure in dogs with cyclooxygenase-2 inhibition

A series of studies has shown that long-term infusion of insulin and glucose does not increase mean arterial pressure (MAP) in dogs, but we have shown that the same infusion protocol or infusion of glucose alone increases arterial pressure in rats. This study tested the hypothesis that infusing glucose alone in dogs, with all insulin derived from endogenous secretion, would increase arterial pressure. Because fructose feeding in dogs also has been shown not to cause hypertension and because we have shown that prostaglandin production increases during insulin and glucose infusion, this study also tested whether prostaglandins prevent the pressor response in dogs. Dogs were instrumented and assigned in random crossover design to long-term cyclooxygenase-2 (COX-2) inhibition. After baseline measurements, glucose was infused in all dogs for 6 days ( approximately 500 g/d IV). Plasma insulin increased 3- to 4-fold and blood glucose increased significantly in both groups. The MAP (measured 24 h/d) response in control dogs was variable but on average tended to increase, although not significantly. In the dogs with COX-2 inhibition, however, MAP increased significantly to a peak of 9+/-2 mm Hg and an average of 6+/-1 mm Hg above control. There was significant sodium and volume retention during glucose infusion and a significant increase in glomerular filtration rate, but there were no between-group differences. Plasma renin activity increased only in the control group. This is the first study to report a long-term pressor response with glucose infusion and hyperinsulinemia in dogs, and it suggests that the inability to detect this relationship previously was due to prostaglandins.

Regulated production of interferon-inducible T-cell chemoattractants by human intestinal epithelial cells

BACKGROUND & AIMS

Human intestinal epithelial cells inducibly express neutrophil and monocyte chemoattractants, yet little is known about the regulated production of T-cell chemoattractants by the intestinal epithelium. IP-10, Mig, and I-TAC are 3 CXC chemokines that are known to act as CD4(+) T-cell chemoattractants.

METHODS

We studied constitutive chemokine expression in human colon, and defined the regulated expression of these chemokines by reverse-transcription polymerase chain reaction, enzyme-linked immunosorbent assay, and immunohistology using cultured human intestinal epithelial cell lines and a novel adaptation of an in vivo human intestinal xenograft model.

RESULTS

IP-10 and Mig were constitutively expressed by normal human colon epithelium, and their cognate receptor, CXCR3, was expressed by mucosal mononuclear cells. Interferon (IFN)-gamma stimulation increased mRNA expression and the polarized basolateral secretion of these chemokines by human colon epithelial cell lines; infection with enteroinvasive bacteria, or stimulation with the proinflammatory cytokines tumor necrosis factor alpha and interleukin 1alpha, strongly potentiated IFN-gamma-induced epithelial cell IP-10, Mig, and I-TAC production. Epithelial cell mRNA and protein expression of IP-10, Mig, and I-TAC were rapidly up-regulated in human intestinal xenografts in response to stimulation with IFN-gamma alone or in combination with IL-1.

CONCLUSIONS

The constitutive and regulated production of the IFN-gamma-inducible chemokines IP-10, Mig, and I-TAC by human intestinal epithelium, and the expression of their cognate receptor, CXCR3, by mucosal mononuclear cells, suggest that the intestinal epithelium can play a role in modulating physiologic and pathologic T cell-mediated mucosal inflammation.

Patients with inflammatory bowel disease (IBD) reveal increased induction capacity of intracellular interferon-gamma (IFN-gamma) in peripheral CD8+ lymphocytes co-cultured with intestinal epithelial cells

Intestinal epithelial cells seem to play a key role during IBD. The network of cellular interactions between epithelial cells and lamina propria mononuclear cells is still incompletely understood. In the following co-culture model we investigated the influence of intestinal epithelial cells on cytokine expression of T cytotoxic and T helper cells from patients with IBD and healthy controls. Peripheral blood mononuclear cells (PBMC) were purified by a Ficoll-Hypaque gradient followed by co-incubation with epithelial cells in multiwell cell culture insert plates in direct contact as well as separated by transwell filters. We used Caco-2 cells as well as freshly isolated colonic epithelia obtained from surgical specimens. Three-colour immunofluorescence flow cytometry was performed after collection, stimulation and staining of PBMC with anti-CD4, anti-CD8, anti-IFN-gamma and anti-IL-4. Patients with IBD (Crohn's disease (CD), n = 12; ulcerative colitis (UC), n = 16) and healthy controls (n = 10) were included in the study. After 24 h of co-incubation with Caco-2 cells we found a significant increase of IFN-gamma-producing CD8+ lymphocytes in patients with IBD. In contrast, healthy controls did not respond to the epithelial stimulus. No significant differences could be found between CD and UC or active and inactive disease. A significant increase of IFN-gamma+/CD8+ lymphocytes in patients with UC was also seen after direct co-incubation with primary cultures of colonic crypt cells. The observed epithelial-lymphocyte interaction seems to be MHC I-restricted. No significant epithelial cell-mediated effects on cytokine expression were detected in the PBMC CD4+ subsets. Patients with IBD-even in an inactive state of disease-exert an increased capacity for IFN-gamma induction in CD8+ lymphocytes mediated by intestinal epithelial cells. This mechanism may be important during chronic intestinal inflammation, as in the case of altered mucosal barrier function epithelial cells may become targets for IFN-gamma-producing CD8+ lymphocytes.

Adhesion molecules expressed on homing lymphocytes in model intestinal epithelia

BACKGROUND & AIMS

The development of intestinal intraepithelial lymphocytes (IELs) requires the movement of lymphocytes into the epithelial compartment (i.e., IEL homing). The rules governing and the biologic consequences of IEL homing are poorly understood. The aims of this study were to examine the adhesion molecules involved in IEL homing and the phenotypic alteration of lymphocytes as a consequence of homing.

METHODS

We previously developed an in vitro IEL homing model consisting of human IEL cell lines and a polarized monolayer of human intestinal epithelial T84 cells. Homing capacity of lymphocytes was assessed by measuring their migration into epithelial monolayers, and phenotypic analysis was performed by flow cytometry.

RESULTS

In this model, approximately 30% of lymphocytes moved into the epithelial monolayer, regardless of the lymphocyte concentration. Flow cytometric screening of adhesion molecules revealed that homed lymphocytes expressed high levels of integrin alphaXbeta2 and alphaEbeta7 and low levels of alpha4beta7 compared with non-homed lymphocytes. In addition, subpopulations sorted as alphaXbeta2(high) or alphaEbeta7(high) independently showed greater homing capacities. After homing, alphaEbeta7 and intercellular adhesion molecule 1 (ICAM-1) on homed lymphocytes were significantly up-regulated, which was consistent with their high expression observed on freshly isolated human IELs. The up-regulation of alphaEbeta7 (but not ICAM-1) was completely dependent on epithelial-derived transforming growth factor beta1 (TGF-beta1). The expression of alphaXbeta2 was observed on a small population of freshly isolated human IELs, and was markedly induced by stimulation. Also, epithelial-derived TGF-beta1 down-regulated the alphaXbeta2 expression (an event likely to occur after homing).

CONCLUSIONS

Our findings indicate a relationship between IEL alphaXbeta2 and alphaEbeta7 expression and homing into intestinal epithelia. We also show that phenotypic alteration of IELs is induced by close interaction with intestinal epithelia as a consequence of homing.

Inhibition of nitric oxide synthesis potentiates hypertension during chronic glucose infusion in rats

Endothelial dysfunction has been proposed to contribute to impaired blood flow control or hypertension in many conditions characterized by hyperinsulinemia or hyperglycemia. However, most studies have focused on whether endothelial dysfunction is present in the established phases of these various hypertensive states, and there is little known concerning the role of the endothelium in the initial stages. This study tested whether nitric oxide production, before endothelial dysfunction develops, plays an important role in counteracting the hypertensive response to chronic glucose infusion. Glucose was infused (18.6 mg/kg per minute IV) for 7 days in 8 normal rats (G) and in 9 rats with a long-term background intravenous infusion of N(G)-nitro-L-arginine methyl ester (L-NAME) at 10 microg/kg per minute (G+L). Mean arterial pressure (MAP), measured 24 hours per day, increased an average of approximately 11 mm Hg in the G rats. L-NAME treatment increased MAP an average of 28+/-2 mm Hg in the G+L rats, and glucose infusion raised MAP >30 mm Hg above that, averaging 155+/-8 mm Hg by day 6. In addition, heart rate increased from an average of 389+/-8 bpm to 441+/-16 bpm by day 6, whereas there was no significant change in the G rats. Glomerular filtration rate decreased significantly with L-NAME treatment and decreased in both groups by day 3 of glucose infusion, reaching lower levels in the G+L rats. These results show that NO is required to minimize the increase in MAP during glucose infusion and suggest that renal and neural mechanisms may be important in mediating that effect.

Fixing the intestinal mucosa in the bone marrow transplant patient: lessons from other intestinal immunodeficiencies and inflammatory disorders

Gastrointestinal inflammation is common following bone marrow transplantation. Key pathogenetic events, such as major histocompatibility complex (MHC) expression on intestinal epithelial cells and local production of cytokines in the gastrointestinal mucosa, are common features of many gastrointestinal inflammatory disorders. Drawing from clinical experience of the treatment of other disorders associated with gastrointestinal inflammation, such as ulcerative colitis and Crohn's disease, a number of therapeutic alternatives may be relevant for the bone marrow transplant patient with significant graft-vs.-host disease (GvHD). Options to consider include therapeutics that alter inflammatory cell migration, anti-inflammatory cytokines, direct neutralization of proinflammatory cytokines, and cytokines that promote epithelial restitution in the gastrointestinal mucosa. In addition, a variety of nutritional and other novel treatments are available, which may improve epithelial function or which have anti-inflammatory actions. Prospective studies of combined nutrient and cytokine-modulating treatments for the bone marrow transplant patient are warranted.

Ligation of intestinal epithelial CD1d induces bioactive IL-10: critical role of the cytoplasmic tail in autocrine signaling

The intestinal epithelium is anatomically positioned to serve as the critical interface between the lumen and the mucosal immune system. In addition to MHC class I and II antigens, intestinal epithelia constitutively express the nonclassical MHC molecule CD1d, a transmembrane molecule with a short cytoplasmic tail expressed as a beta(2)-microglobulin-associated 48-kDa glycoprotein and novel beta(2)-microglobulin-independent 37-kDa nonglycosylated protein on intestinal epithelia. At present, it is not known whether extracellular ligands can signal intestinal epithelial CD1d. To define signaling of CD1d cytoplasmic tail, retrovirus-mediated gene transfer was used to generate stable cell lines expressing wild-type CD1d or a chimeric molecule (extracellular CD1d and cytoplasmic CD1a), and surface CD1d was triggered by antibody crosslinking. Although wild-type CD1d was readily activated (tyrosine phosphorylation), no demonstrable signal was evident in cell lines expressing the chimeric molecule. Subsequent studies revealed that anti-CD1d crosslinking specifically induces epithelial IL-10 mRNA and protein and is blocked by the tyrosine kinase inhibitor genistein. Further studies addressing epithelial-derived IL-10 revealed that anti-CD1d crosslinking attenuates IFN-gamma signaling and that such attenuation is reversed by addition of functionally inhibitory IL-10 antibodies. These results define signaling through surface CD1d, and, importantly, they demonstrate that this pathway may serve to dampen epithelial proinflammatory signals.

The nonclassical class I molecule CD1d associates with the novel CD8 ligand gp180 on intestinal epithelial cells

Previous studies have shown that normal intestinal epithelial cells (IECs) are able to selectively activate CD8(+) T cells with suppressor activity, inducing proliferation associated with the activation of both the CD8-associated kinase p56(lck) and the T cell receptor (TCR)-associated kinase p59(fyn). This process appears to relate in part to a 180-kDa IEC surface glycoprotein, gp180, which binds to CD8 and activates CD8-associated p56(lck). However, purified gp180 alone is unable to induce T cell proliferation and does not activate p59(fyn). Because the class Ib molecule CD1d is expressed by IECs and monoclonal antibodies (mAbs) against CD1d inhibit IEC-induced proliferation of CD8(+) T cells, co-immunoprecipitation and enzyme-linked immunosorbent assay studies were performed, which demonstrated an association of gp180 and CD1d on the IEC surface. Interestingly, the activation of p59(fyn) in IEC-T cell co-cultures was blocked by the anti-CD1d mAb D5 but not by the anti-gp180 mAb B9. Conversely, treatment of IECs with mAb B9 inhibited IEC-induced activation of p56(lck) but not p59(fyn). More directly, a human CD1d cDNA (FO-1 D5) transfectant was able to activate p59(fyn) but not p56(lck). These data suggest that the CD1d-gp180 complex on the surface of IECs can be recognized by the TCR-CD8 co-receptor, resulting in the activation of CD8(+) T cells.

Biochemical characterization of CD1d expression in the absence of beta2-microglobulin

CD1d is a major histocompatibility complex class I-like molecule that exhibits a distinct antigen processing pathway that functions in the presentation of hydrophobic antigens to T cells. CD1d has been previously shown to be expressed on the cell surface of human intestinal epithelial cell lines in vivo and a transfected cell line in vitro independently of beta2-microglobulin (beta2m). To define the relationship between CD1d and beta2m and characterize the biochemical structure of CD1d in the absence of beta2m, we have used a newly generated series of CD1d transfectants and CD1d-specific antibodies. These studies show that in the absence of beta2m, CD1d is expressed on the cell surface as a 45-kDa glycoprotein that is sensitive to endoglycosidase-H and is reduced to 37-kDa after N-glycanase digestion. In contrast, in the presence of beta2m, CD1d is expressed on the cell surface as a 48-kDa endoglycosidase-H-resistant glycoprotein. Pulse-chase metabolic labeling studies demonstrate that acquisition of endoglycosidase-H resistance of CD1d is observed in the presence of beta2m but not in the absence of beta2m even after a 24-h chase period. Thus, CD1d is able to be transported to the cell surface independently of beta2m; however, in the absence of beta2m, the glycosylation pattern of CD1d is altered and consistent with an immature glycoprotein.

Immunolocalization of CD1d in human intestinal epithelial cells and identification of a beta2-microglobulin-associated form

In order to better understand the role of intestinal CD1d, we sought to define the cellular localization and further characterize the biochemical structure of CD1d in human intestinal epithelial cells (IEC). Using a CD1d-specific rabbit anti-gst-CD1d antibody, immunoprecipitation of radiolabeled cell surface proteins detected a previously identified 37 kDa protein as well as a 48-50 kDa protein which were confirmed by Western blotting with a CD1d-specific mAb, D5. Immunoprecipitation of protein lysates with the CD1d-specific mAb, D5 and 51.1.3, and the beta2-microglobulin (beta2m)-specific mAb, BBM.1, followed by N-glycanase digestion and Western blotting with the D5 mAb showed that the 48-50 kDa protein was a beta2m-associated, CD1d glycoprotein. CD1d was immunolocalized to the apical and lateral regions of native small and large intestinal IEC as defined by confocal laser microscopy using the D5 mAb and the rabbit anti-gst-CD1d antibody. In addition, a large apical intracellular pool of CD1d was identified. Identical observations were made with polarized T84 cells. Selective biotin labeling of apical and basolateral cell surfaces followed by immunoprecipitation with the D5 mAb, N-glycanase digestion and avidin blotting confirmed the presence of glycosylated CD1d on both cell surfaces and immunolocalization of the 37 kDa non-glycosylated form of CD1d to the apical cell surface. These studies show that CD1d is located in an ideal position for luminal antigen sampling and presentation to subjacent intraepithelial lymphocytes.

Role of neuronal nitric oxide synthase in Dahl salt-sensitive hypertension

The goal of this study was to determine the role of neuronal nitric oxide synthase (nNOS) in the arterial pressure, renal hemodynamic, and renal excretory changes that occur in Dahl salt-resistant (DR) and salt-sensitive (DS) rats during changes in Na intake. Fifty-three DR and DS rats/Rapp strain of 7 to 8 weeks of age with indwelling arterial and venous catheters were subjected to low (0.87 mmol/d) or high (20.6 mmol/d) Na intake beginning 2 days before the start of the control period. Measurements were made during a 5-day control period followed by a 5-day period of nNOS inhibition with intravenous 7-nitroindazole (7NI, 1.67 mg. kg-1. h-1) or vehicle infusion. After 5 days of 7NI, mean arterial pressure increased to 120+/-6% control in the DR-high Na, 7NI rats compared with 98+/-1% control (P<0.05) in the DR-high Na alone rats. After 5 days of 7NI, DS-high Na rats, which had a control arterial pressure 31 mm Hg higher than the comparable DR rats, increased their arterial pressure to 114+/-3% control, which was not significantly different from the DS-high Na alone pressure of 110+/-2% control. No significant changes occurred in glomerular filtration rate, effective renal plasma flow, urinary Na excretion, or urine volume because of 7NI. However, plasma renin activity decreased significantly in DR and DS rats on low Na intake with 7NI infusion. The data demonstrate that the highly salt-resistant DR rat became salt-sensitive during nNOS inhibition with 7NI. However, the arterial pressure of the DS rat was not affected by 7NI. This suggests that nitric oxide produced by nNOS in the DR rat normally helps to prevent salt-sensitive hypertension and that low functional levels of nNOS in the DS rat may contribute to its salt-sensitivity.