Identification and upregulation of galactose/N-acetylgalactosamine macrophage lectin in rat cardiac allografts with arteriosclerosis

Sweet preferences of MGL: carbohydrate specificity and function

C-type lectins play important roles in both innate and adaptive immune responses. In contrast to the mannose- or fucose-specific C-type lectins DC-SIGN and mannose receptor, the galactose-type lectins, of which only macrophage galactose-type lectin (MGL) is found within the immune system, are less well known. MGL is selectively expressed by immature dendritic cells and macrophages with elevated levels on tolerogenic or alternatively activated subsets. Human MGL has an exclusive specificity for rare terminal GalNAc structures, which are revealed on the tumor-associated mucin MUC1 and CD45 on effector T cells. These findings implicate MGL in the homeostatic control of adaptive immunity. We discuss here the functional similarities and differences between MGL orthologs and compare MGL to its closest homolog, the liver-specific asialoglycoprotein receptor (ASGP-R).

LPS suppresses expression of asialoglycoprotein-binding protein through TLR4 in thioglycolate-elicited peritoneal macrophages

Macrophages are known to express various types of endocytosis receptors that mediate the removal of foreign pathogens. Macrophage asialoglycoprotein-binding protein (M-ASGP-BP) is a Gal/GalNAc-specific lectin, which functions as an endocytosis receptor. We found here that LPS is able to down-regulate the mRNA expression of M-ASGP-BP in a time-dependent manner using thioglycolate-elicited rat and mouse peritoneal macrophages. However, LPS does not modulate the mRNA expression of M-ASGP-BP from macrophages of C3H/HeN mice, which have a point mutation of TLR4, the primary LPS receptor. Furthermore, an inhibitor of NF-kappaB was observed to efficiently block the suppressive effect of LPS on M-ASGP-BP as well as to inhibit the phosphorylated IkappaB. These results demonstrate that the mRNA expression of M-ASGP-BP is down-regulated by the LPS-mediated TLR4 pathway involving NF-kappaB activation, suggesting that engagement of M-ASGP-BP by LPS may yield a negative signal that interferes with the LPS-induced positive signals mediated by proinflammatory cytokines.

Redistributions of macrophages expressing the macrophage galactose-type C-type lectin (MGL) during antigen-induced chronic granulation tissue formation

Cell surface lectins are known to regulate trafficking of cells in the immune system, yet the role of macrophage galactose-type C-type lectin 1 and 2 (MGL1/2) is poorly understood. In this study, antigen-specific chronic inflammation was induced in a subcutaneous air pouch model in mice, and distribution of cells expressing MGL1/2 was investigated. Azobenzenearsonate-conjugated acetylated BSA, used as an antigen, was introduced into an air pouch of immunized mice, and tissue formation and distribution of MGL1/2-positive cells in the sub-dermal regions was examined. Thickness of the inflammatory tissue and number of MGL1/2-positive cells simultaneously reached the maximum at day 4 and returned to the control level at day 6 or 8. When additional antigenic challenges were given, a chronic granulation tissue, which had two distinct layers, was generated. In the chronic tissue, CD11b-positive/MGL1/2-negative cells were abundant in the area close to the antigenic stimulus, while the area far from the antigenic stimulus was dominated by MGL1/2-positive/CD11b-negative or -low cells. Flow cytometric analyses of isolated cells from the granulation tissue revealed that MGL1/2-positive cells expressed MHC class II at high levels, CD11b at low levels but no CD11c. MGL1/2-positive and -negative fractions were separated from cells in the granulation tissue and a higher level of IL-1alpha messenger RNA than negative populations was detected in the MGL1/2-positive fraction by the semi-quantitative reverse transcription-PCR method. IL-1alpha production by MGL1/2-positive cells was also immunohistochemically detected. Results suggest that MGL1/2-positive cells represent a distinct sub-population of macrophages, having unique functions in the generation and maintenance of granulation tissue induced by antigenic stimuli.

Generation of mice deficient for macrophage galactose- and N-acetylgalactosamine-specific lectin: limited role in lymphoid and erythroid homeostasis and evidence for multiple lectins

Macrophage receptors function in pattern recognition for the induction of innate immunity, in cellular communication to mediate the regulation of adaptive immune responses, and in the clearance of some glycosylated cells or glycoproteins from the circulation. They also function in homeostasis by initiating the engulfment of apoptotic cells. Evidence has suggested that macrophage receptors function to recognize cells that are destined for programmed cell death but not yet overtly apoptotic. We have examined the function of a macrophage receptor specific for unsialylated glycoproteins, known as the mouse macrophage galactose- and N-acetylgalactosamine-specific lectin (mMGL) (Ii et al., J. Biol. Chem. 265:11295-11298, 1990; Sato et al., J. Biochem. [Tokyo] 111:331-336, 1992; Yamamoto et al., Biochemistry 33:8159-8166, 1994). With targeted disruption, we tested whether mMGL is necessary for macrophage function, controlled thymic development, the loss of activated CD8 T cells, and the turnover of red blood cells. Evidence indicates that mMGL may play a nonessential role in several of these macrophage functions. Experiments are presented that indicate the existence of another galactose- and N-acetylgalactosamine-recognizing lectin distinct from mMGL. This may explain the absence of a strong phenotype in mMGL-deficient mice.

Heart transplantation changes the expression of distinct gene families

We took advantage of the combination of a rat heart transplantation model with a modified differential display RT-PCR method to identify transcriptome changes in the right atria from transplanted compared with native hearts. Based on sequence homology search, the 37 cDNAs differentially displayed both 2 and 7 days posttransplantation were categorized into 7 unknown transcripts, 16 expressed sequence tags (ESTs), and 14 partially or completely characterized genes. The last group cDNAs, validated by relative RT-PCR, belonged to diverse gene families involved in specific metabolisms, protein synthesis, cell signaling, and transcription. Furthermore, we identified differential transcripts corresponding to denervation and fetal gene reexpression. We found coordinate downregulation of genes involved in energy metabolism and protein synthesis regulation, similar to that reported for senescent skeletal muscle. From these transcriptome changes, we propose that heart transplants and senescent muscles share common molecular mechanisms.

Hepatocyte growth factor prevents the development of chronic allograft nephropathy in rats

Long-term renal isografts in humans and laboratory animals exhibit features similar to those of chronic allograft nephropathy (CAN), indicating that antigen-independent factors, such as acute renal ischemia, are likely to be involved in the development of CAN. Hepatocyte growth factor (HGF) has been demonstrated to play a renotropic role in renal regeneration and protection from acute ischemic injury. This study was thus conducted to investigate the effect of HGF on the development of CAN, using an established rat model. HGF was administered daily (100 microg/d, intravenously) for 4 wk after engraftment. Control animals received saline solution. Allografts from control animals exhibited early evidence of severe structural collapse and necrotic cell death in the proximal tubules and outer medulla, with mononuclear cell infiltration, within 1 wk after engraftment. This was followed by sequential upregulation of adhesion molecules and cytokines, accompanied by dense macrophage infiltration. Fibrogenic events, as indicated by marked increases in transforming growth factor-beta1 expression and the accumulation of smooth muscle alpha-actin, occurred during the same period. Control animals ultimately developed features typical of CAN, with functional deterioration and severe histologic changes; a survival rate of 50.6% by 32 wk was observed. In contrast, remarkably little early injury and no late fibrogenic events were observed for the HGF-treated group. All treated animals survived, with well preserved graft function, during the 32-wk follow-up period. These results indicate that renal protection and recovery from early allograft injury with HGF treatment greatly contribute to a reduction of susceptibility to the subsequent development of CAN in a rat model. The potential application of HGF in the prevention of CAN warrants further attention.

Mast cells in acute and chronic rejection of rat cardiac allografts--a major source of basic fibroblast growth factor

BACKGROUND

Studies of cardiac allograft arteriosclerosis, i.e., chronic rejection, have largely focused on mononuclear inflammatory cell infiltrates in the vascular wall and periphery of the occluded vessels. The purpose of this study was to investigate the role of mast cells in the development of acute and chronic rejection in rat cardiac allografts.

METHODS

In the acute rejection model, transplant recipients were not treated with immunosuppressants, and the grafts were removed 5 days after transplantation at the time of severe acute rejection. In the chronic rejection model, the recipients were administered triple-drug immunosuppression, and the grafts were removed 90 days after transplantation.

RESULTS

During acute rejection, the number of mast cells was not increased, but the localization pattern differed from that of syngeneic grafts. In acute rejection, mast cells were located in the perivascular region of the allografts, but in syngeneic grafts, mast cells had a more interstitial location. In the chronic rejection model, the cardiac allografts with severe intimal thickening showed large numbers of mast cells at perivascular sites of occluded intramyocardial vessels and in the interstitium. Linear regression analysis revealed a significant correlation between the numbers of perivascular and interstitial mast cells and the intensity of intimal thickening. The majority of mast cells showed positive immunoreactivity to basic fibroblast growth factor (bFGF). Macrophage bFGF expression was not so prominent, but macrophages were more frequent in numbers. Tumor necrosis factor-alpha expression was detected mainly in macrophages and in only a few mast cells. When the intensity of arteriosclerosis was decreased by an increase in the intensity of immunosuppression, the numbers of intragraft mast cells and other mononuclear cells, and also the production of their respective cytokines, bFGF and tumor necrosis factor-alpha, gradually diminished.

CONCLUSIONS

Taken together, our data show that the intensity of intramyocardial mast cell infiltration was associated with the intensity of chronic inflammation and allograft arteriosclerotic changes, but not with acute rejection, and that mast cells, in addition to macrophages, are a major source of myocardial bFGF. The results also demonstrate that when the T-cell activation pathway is blocked using cyclosporin, the number of mast cells is decreased. Cyclosporin may have affected the cytokine production that interfered with both the mast cell-dependent initiation and the leukocyte- and mast cell-dependent amplification and progression of the immune responses influenced by mast cell-leukocyte cytokine cascades. bFGF produced by mast cells may contribute to enhanced inflammation, neovascularization, and fibrosis during cardiac allograft arteriosclerosis.

Expression of macrophage asialoglycoprotein-binding protein is induced through MAPK classical pathway

Macrophage asialoglycoprotein-binding protein (M-ASGP-BP) is a Gal/GalNAc-specific lectin, which functions as an endocytosis receptor. We found that the expression of M-ASGP-BP mRNA in bone marrow cells was induced during the differentiation into macrophages. To investigate the mechanism by which M-ASGP-BP mRNA expression is induced, we used U937 cells as a model. Treatment of U937 cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) resulted in M-ASGP-BP mRNA expression within 6 h. This induction was completely inhibited by PKC inhibitors, calphostin C, and staurosporine. Furthermore, MAP kinase inhibitors PD98059, but not SB202190, blocked M-ASGP-BP mRNA expression. These data indicate that M-ASGP-BP mRNA expression occurs through the activation of PKC and the MAPK classical pathway in the course of cell differentiation into macrophages.

Role of the macrophage galactose lectin in the uptake of desialylated LDL

Desialylated low density lipoprotein (LDL) is rapidly taken up and accumulated by both peripheral blood monocytes and cells isolated from human arterial intima consisting predominantly of smooth muscle cells. It is shown that thioglycollate (TG)-elicited mouse macrophages and mouse peritoneal macrophages stimulated with lipopolysaccharide (LPS) show increased expression of a membrane-bound, galactose-specific lectin that could be responsible for this uptake. In LPS-stimulated macrophages accumulation of desialylated LDL is increased ca. 2.6-fold. Accumulation of acetylated LDL in the same cells is reduced, suggesting that the galactose-specific lectin might be responsible for the uptake of desialylated LDL. Transfection of cells with the mouse macrophage Gal/GalNAc-specific lectin (MMGL) increased their capacity to take up asialofetuin (ASF) and, to a smaller extent, desialylated LDL. The uptake of desialylated LDL was small, most likely due to the high k(d) of MMGL for biantennary oligosaccharides as found on LDL, and low concentration of LDL achieved in tissue culture experiments. The data suggest that the expression of galactose-specific lectins can be elevated under inflammatory conditions, and that these receptors could contribute to foam cell formation under conditions of high desialylated LDL concentration, as might be found in arterial intima.

Epitope mapping of monoclonal antibodies specific for a macrophage lectin: a calcium-dependent epitope is in the carbohydrate recognition domain

Mouse macrophage galactose/N-acetylgalactosamine-specific calcium-type lectin (mMGL) has a calcium-dependent conformational epitope which is a ligand-induced binding site. A monoclonal antibody (mAb) specific for this epitope (LOM-11) stabilize lectin activity. We performed mapping for this conformational epitope using trypsin fragments that contain a carbohydrate recognition domain (CRD) and chimeric recombinant proteins between mMGL and a human counterpart of this molecule. Binding site for the mAb LOM-11 was mapped within the C-terminal 59 amino acids of CRD. Binding sites for all four mAbs that block carbohydrate ligand binding were also mapped in the C-terminal half of CRD. These results indicated that the calcium-dependent site potentially involved in protein-protein interaction, regulatory or for coordinated binding, is mapped within CRD in addition to the independent carbohydrate binding site, and that both of the distinct sites may have spatial proximity.

Identification of a stress-induced protein during human trophoblast differentiation by differential display analysis

Differentiation of human placental trophoblast is characterized by a process during which mononuclear villous cytotrophoblasts fuse to form a multinucleate syncytium. This event is associated with dramatic changes in gene expression. In the present study, we have applied a sensitive approach-differential display analysis-to evaluate changes in gene expression during in vitro forskolin-induced differentiation of a model of human trophoblast, the choriocarcinoma BeWo. We identified seven genes that were up-regulated; their expression and function have not previously been reported in trophoblast. Four up-regulated genes were novel upon comparison of their sequences to the GenBank database. The other three genes encode human cytochrome p450 IIC, inosine monophosphate dehydrogenase type II, and reducing agent and tunicamycin-responsive protein (RTP). Northern blot analysis revealed that RTP mRNA expression was induced to 3-fold in BeWo after 24-h incubation with forskolin and increased up to 11-fold by 72 h of forskolin treatment. The expression pattern of RTP was further investigated by in situ hybridization on second trimester and term placenta tissues. RTP mRNA was predominantly expressed in syncytiotrophoblasts in both second trimester and term placentae. The expression of RTP gene in BeWo cells was protein kinase C dependent. This is the first description of RTP gene expression in placenta and the first study elucidating the signaling pathway involved in the regulation of RTP gene expression. These results suggest that RTP may play a role in trophoblast cell proliferation and differentiation.

Interaction of human macrophage C-type lectin with O-linked N-acetylgalactosamine residues on mucin glycopeptides

A fluorescein-labeled synthetic peptide, PTTTPITTTTK, was converted into O-glycosylated glycopeptides with various numbers of attached N-acetyl-D-galactosamines (GalNAcs) by in vitro glycosylation with UDP-GalNAc and a microsomal fraction of LS174T human colon carcinoma cells. Glycopeptides with 1, 3, 5, and 6 GalNAc residues (G1, G3, G5, and G6) were obtained, and their sizes were confirmed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Their sequences were determined by a peptide sequencer to be PTTTGalNAcPITTTTK for G1, PTGalNAcTTPITGalNAcTGalNAcTTK for G3, PTTGalNAcTGalNAcPITGalNAcTGalNAcTGalNAcTK for G5, and PTGalNAcTGalNAcTGalNAcPITGalNAcTGalNAcTGalNAcTK for G6. A calcium-type human macrophage lectin (HML) was prepared in a recombinant form, and its interaction with these glycopeptides was investigated by surface plasmon resonance (SPR) spectroscopy and fluorescence polarization. The affinity of recombinant HML (rHML) for immobilized glycopeptides increased, as revealed by SPR, in parallel with the number of GalNAc. The highest affinity was obtained when the G6-peptide was immobilized at high density. Fluorescence polarization equilibrium-binding assays also revealed that the affinity of rHML for soluble gly-copeptides increased, depending on the number of attached GalNAcs. Carbohydrate recognition domain (CRD) fragments of HML were prepared, and their affinity for these four glycopeptides was also determined, this affinity was apparently lower than that of rHML. Affinity constants of rHML for the G3- and G5-peptides were 11- and 38-fold higher, respectively, than for the G1-peptide, whereas those of CRD fragments were only 2- and 6-fold higher, respectively. A chemical cross-linking study revealed that rHML but not recombinant CRD forms trimers in an aqueous solution. Thus, preferential binding of densely glycosylated O-linked glycopeptides should be due to the trimer formation of rHML.

Assessment of peripheral tolerance in anti-CD4 treated C57BL/6 mouse heart transplants recipients

The study was designed to compare second heart and skin grafts and in vitro assays as a means of assessing peripheral tolerance in C57BL/6 mice. Vascularized heterotopic BALB/c hearts were placed in C57BL/6 recipients treated with anti-CD4, GK1.5 (1 mg total per 20 g mouse i.p. on days 0, 1, 2, 3). Those mice in which hearts survived for >60 days were challenged with donor and third-party (CBA) skin grafts or with second heart grafts, of donor or third-party origin, attached to the carotid artery and jugular vein. In vitro alloreactivity was assessed by mixed lymphocyte reactions (MLR) and cell mediated lympholysis (CML) using recipient spleen cells. Parenchymal damage, cellular infiltration and vascular disease were assessed from the histology of long-term allografts and isografts. Allografts in untreated recipients were rapidly rejected while isografts survived > 100 days. Primary allografts in anti-CD4 treated recipients also survived > 100 days, as did donor strain secondary heart transplants given at >60 days after the first graft. Third-party hearts were rapidly rejected, as were donor and third-party skin grafts placed on recipients with long-term allografts. These recipients showed low MLR response to both donor and third-party stimulators and donor-specific suppression of CML at 60 days post graft. Long-surviving heart allografts all showed evidence of parenchymal damage and vascular intimal thickening. Thus in the BALB/c to C57BL/6 donor-recipient strain combination, hearts, but not skin grafts, could be used to demonstrate peripheral tolerance, which seemed to be both organ and major histocompatibility complex (MHC) specific. Despite long survival, BALB/c hearts all showed evidence of parenchymal damage and vascular intimal thickening, a sign of chronic rejection.

Identification of differentially expressed mRNAs in human fetal liver across gestation

Differential gene expression, with its precise start and stop times, is believed to be critical for the programmed development of new cells and tissues. Within the developing fetus, one tissue of particular interest is fetal liver. This organ undergoes rapid changes in the pathway toward liver development in utero since it is also the major site of hematopoiesis, until bone marrow hematopoiesis predominates. Believing that patterns would emerge from the bi-weekly large-scale inspection of expressed genes in the fetal liver, we employed differential display reverse transcription-polymerase chain reaction (DDRT-PCR) as ourprimary inspection tool. Using DDRT-PCR, we isolated cDNAs differentially expressed throughout fetal liver development and in adult liver. We displayed approximately 25 000 cDNAs from 10 and 24 week fetal liver and adult liver. From this initial screen, we determined that approximately 0.1-1% of the mRNA population undergoes expression changes. We extracted, purified and sequenced 25 differentially displayed cDNA bands. Fourteen cDNAs had similarities to known genes, while 11 cDNAs were not similar to any characterized gene. The differentially expressed cDNAs from known genes present in fetal liver include alpha-fetoprotein, stem cell factor, erythroid alpha-spectrin, 2,3-bisphosphoglycerate mutase, insulin-like growth factor-2, porphobilinogen deaminase and Mac30. The differentially expressed cDNAs present in adult liver but not in 10 week fetal liver were nicotinamide deaminase, human fibrinogen-related protein and alpha-acid glycoprotein. The majority of differentially expressed genes found during this effort appear to be turned on during organogenesis, however, some genes were found that are apparently turned off completely.

Differential immediate early gene expression in conditional hepatitis B virus pX-transforming versus nontransforming hepatocyte cell lines

We report construction and characterization of tetracycline-controlled hepatitis B virus pX-expressing hepatocyte (AML12) cell lines. These cell lines were constructed in AML12 clonal isolates (clones 3 and 4), which express constitutively the tetracycline-controlled transactivator. Since pX is implicated in HCC, this immortalized hepatocyte model system was used to investigate the mechanism of pX in transformation. Clonal isolates of 3pX and 4pX lineages display conditional synthesis of pX mRNA and protein and a 2-fold increase in growth saturation density following tetracycline removal, implicating pX in monolayer overgrowth. Interestingly, only 3pX clones display pX-dependent anchorage independence. Clone 3 lineages express hepatocyte nuclear factor-1alpha and hepatocyte-specific marker genes; clone 4 lineages express hepatocyte nuclear factor-1beta and reduced levels of hepatocyte-specific marker genes, suggesting the importance of the differentiated hepatocyte in pX-mediated oncogenic transformation. Importantly, 3pX and 4pX lineages display differential expression of immediate early genes c-fos and ATF3. The pX-transforming 3pX lineage displays early, pX-dependent induction of ATF3 and prolonged induction of c-fos. The nontransforming 4pX cells display an absence of pX-dependent ATF3 induction and transient induction of c-fos. Our results support the direct link of pX expression to oncogenic transformation in 3pX lineage clones and underscore the advantage of this conditional cellular model system for studying mechanisms of pX-mediated oncogenesis.

Revolution through genomics in investigative and discovery toxicology

The remarkable technologic and methodologic advances spurred on by the Human Genome Project are being applied throughout the life sciences. In the field of toxicology, high-resolution assays now make it possible to discover virtually all the differences in gene expression brought on by exposure to a particular xenobiotic. There are 2 principal approaches used to build a catalog of changes in gene expression: hybridization microarrays and gel-based methods, such as differential display and AFLP-based mRNA finger-printing. The power of such approaches is exemplified by the identification of more than 300 genes that differ in expression level by at least 2-fold in response to the nongenotoxic rodent liver carcinogen phenobarbital.

Coordinated binding of sugar, calcium, and antibody to macrophage C-type lectin

Mouse macrophage galactose/N-acetylgalactosamine-specific C-type lectin (MMGL) is a type II transmembrane glycoprotein belonging to the C-type lectin family. Our development of monoclonal antibodies led us to discover that a calcium-dependent conformational change is detected by an antibody (termed mAb LOM-11) and that the antibody's binding to the respective site locks the lectin in an active conformation. These findings correspond to the divalent cation-mediated regulatory mechanisms in a family of cell adhesion molecule integrins that have gained much attention. We now provide direct evidence that mAb LOM-11 increases the affinity of the lectin for calcium ions as a mechanism for the conformational lock using a soluble recombinant form of MMGL (rML) produced in bacteria. Furthermore, we discovered by using an enzyme-linked immunosorbent assay that specific monosaccharides induced a binding site for mAb LOM-11 on the immobilized rML under low calcium environments. We also demonstrated that cell surface MMGL on a transfectant cell line underwent a conformational change upon addition of calcium or ligands, as detected by the binding of mAb LOM-11. These properties are reminiscent of ligand-induced binding sites defined for integrins. The present results suggest a possibility that the mAb LOM-11 binding site on the lectin may be a site at which protein-protein interaction helps to fine tune the specificity of the C-type lectins by means of coordinated recognition mechanisms.

Cloning of a novel C-type lectin expressed by murine macrophages

We report the cloning of a novel macrophage-restricted C-type lectin by differential display polymerase chain reaction. This molecule, named mouse macrophage C-type lectin, is a 219-amino acid, type II transmembrane protein with a single extracellular C-type lectin domain. Northern blot analysis indicates that it is expressed in cell lines and normal mouse tissues in a macrophage-restricted manner. The cDNA and genomic sequences of mouse macrophage C-type lectin indicate that it is related to the Group II animal C-type lectins. The mcl gene locus has been mapped between the genes for the interleukin-17 receptor and CD4 on mouse chromosome 6, the same chromosome as the mouse natural killer cell gene complex.

IL-1 beta alters the expression of the receptor tyrosine kinase gene r-EphA3 in neonatal rat cardiomyocytes

To identify proinflammatory cytokine responsive genes in the myocardium, we used differential display to study RNA isolated from neonatal rat cardiac myocytes treated with tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta). Sequence analysis of differential display products confirmed by reverse Northern blots revealed one clone as the partial sequence of an Eph-related receptor tyrosine kinase (r-EphA3). In cardiac myocytes, 36-h exposure to TNF-alpha and IL-1 beta reduced r-EphA3 transcripts to 59.9% (P < 0.01) of control levels; this effect was largely dependent on IL-1 beta. Western blot analysis showed that changes in r-EphA3 protein levels reflect that seen for transcripts. Cardiac nonmyocytes expressed substantially lower levels of r-EphA3. Full-length r-EphA3 cDNA clone (3,077 base pair) yielded an amino acid sequence with 90-98% homology to the Eph receptor human EphA3, chick EphA3, and mouse EphA3. In the adult rat, r-EphA3 transcripts were most abundant in the heart, brain, and lung. These results suggest that IL-1 beta may exert its effect on cardiac myocytes at least in part by altering r-EphA3 expression.

Effects of leflunomide and deoxyspergualin in the guinea pig-->rat cardiac model of delayed xenograft rejection: suppression of B cell and C-C chemokine responses but not induction of macrophage lectin

BACKGROUND

If complement (C) activation is prevented or the host is C depleted, discordant vascularized xenografts undergo delayed xenograft rejection (DXR), characterized by graft infiltration by macrophages (MO) and natural killer (NK) cells, endothelial cell activation, and widespread fibrin deposition. Given a lack of effect of T cell-directed therapies on development of DXR, we evaluated two novel agents, 15-deoxyspergualin (DSG) and leflunomide (LEF), with reported anti-B-cell and/or anti-MO actions.

METHODS

DSG and LEF were administered to C-depleted, splenectomized rat recipients of guinea pig cardiac xenografts, and their effects on graft survival and production of anti-guinea pig antibodies were determined. Serial intragraft events were studied by immunohistology using monoclonal antibodies to rat leukocytes, cytokines, and novel proteins, including rat MO lectin, which in other systems is important to MO binding, activation, and target cell killing.

RESULTS

Median graft survival was 62 hr in cobra venom factor (CVF)-treated controls versus 108 hr (DSG), 129 hr (LEF), and 120 hr (DSG and LEF; all groups P<0.01 vs. CVF alone). LEF and DSG each decreased (immunoglobulin M [IgM]) or abrogated (IgG) posttransplant production of anti-guinea pig antibodies. Immunohistologic studies showed that each agent also inhibited graft infiltration by NK and T cells, and expression of various cytokines, including the chemokine monocyte chemoattractant protein-1 (MCP-1), but did not affect the tempo or extent of MO infiltration. Consistent with this, the rapid induction of MO lectin postxenografting, and induction of MO lectin by rat MO exposed to guinea pig cells in vitro, were unaffected by therapy with DSG and/or LEF.

CONCLUSIONS

LEF or DSG along with CVF can result in the longest prolongation of xenograft survival yet reported in this model, in conjunction with a dampening of host mononuclear cell responses, including suppression of B cell activation. However, the persistent influx of MO in this model, despite lack of C-, Fc receptor- or apparent chemokine-dependent mechanisms, suggests the presence of additional mechanisms for cell recruitment and activation. It was of importance that, in this regard, although MO depletion is technically difficult and can lead to undesired effects, the demonstration of rapid MO lectin induction postxenografting indicates opportunities for blockade of MO recruitment and functions during DXR by use of anti-MO lectin monoclonal antibodies or administration of competing sugars.

Effect of chemical structure of hydrogels on the adhesion and phenotypic characteristics of human monocytes such as expression of galectins and other carbohydrate-binding sites

The reactivity of diverse immune aspects to the presence of synthetic polymers represents one of the most important aspects of implantable device biocompatibility. In this report, we show the effect of the chemical structure of a synthetic polymer support on monocyte adhesion and selected phenotypic characteristics in vitro as a model for the initial steps of non-self-recognition of an implant. The extent of monocyte adhesion was significantly influenced by the support chemistry. The highest level of monocyte adhesion was observed on a surface copolymer of 2-hydroxyethyl methacrylate with dimethyl aminoethyl methacrylate relative to results of experiments in which poly(2-hydroxyethyl methacrylate) or the copolymer of 2-hydroxyethyl methacrylate with the sodium salt of methacrylic acid was used. Cell adhesion to the polymers tested and to glass was accompanied by enhanced expression of the carbohydrate-binding sites tested for asialoglycoprotein beta-galactosides such as galectins, beta-N-acetylgalactosamine, alpha-mannoside, specific lectin for heparin as well as the lymphokine-macrophage migration inhibitory factor in the monocytes tested. These results suggest the importance of monocyte adhesion to the biomaterial surface for their development into macrophages and further non-self-recognition of the implanted device.

Animal lectins

Protein and lipid glycosylation is no longer considered as a topic whose appeal is restricted to a limited number of analytical experts perseveringly pursuing the comprehensive cataloguing of structural variants. It is in fact arousing curiosity in various areas of basic and applied bioscience. Well founded by the conspicuous coding potential of the sugar part of cellular glycoconjugates which surpasses the storage capacity of oligonucleotide- or oligopeptide-based code systems, recognition of distinct oligosaccharide ligands by endogenous receptors, i.e. lectins and sugar-binding enzymes or antibodies, is increasingly being discovered to play salient roles in animal physiology. Having inevitably started with a descriptive stage, research on animal lectins has now undubitably reached maturity. Besides listing the current categories for lectin classification and providing presentations of the individual families and their presently delineated physiological significance, this review places special emphasis on tracing common structural and functional themes which appear to reverberate in nominally separated lectin and animal categories as well as lines of research which may come to fruition for medical sciences.

The interaction of agouti signal protein and melanocyte stimulating hormone to regulate melanin formation in mammals

Important regulatory controls of melanogenesis that operate at the subcellular level to modulate the structural and/or the functional nature of the melanins and melanin granules produced in melanocytes are reviewed. Melanocyte stimulating hormone and agouti signal protein have antagonistic roles and possibly opposing mechanisms of action in the melanocyte. In the mouse, melanocyte stimulating hormone promotes melanogenic enzyme function and elicits increases in the amount of eumelanins produced, while agouti signal protein reduces total melanin production and elicits the synthesis of pheomelanin rather than eumelanin. We are now beginning to understand the complex controls involved in regulating this switch at the molecular and biochemical levels. The quality and quantity of melanins produced by melanocytes have important physiological consequences for melanocyte function and undoubtedly play important roles in the various functions of the melanins per se, including hair and skin coloration and photoprotection.

Delayed xenograft rejection

Despite considerable progress in understanding the mechanisms of discordant xenograft rejection, and overcoming hyperacute rejection through targeting of complement or antibody, vascularized xenografts are typically rejected within days. Here, Fritz Bach and colleagues discuss the importance of endothelial cell activation, platelet aggregation and other aspects of thrombosis, as well as the contribution of host natural killer cell and monocyte activation in overcoming this next barrier to prolonged xenograft survival.

Allograft inflammatory factory-1. A cytokine-responsive macrophage molecule expressed in transplanted human hearts

Allograft inflammatory factor-1 (AIF-1), a cytokine-responsive macrophage molecule, was originally identified and cloned from rat cardiac allografts with chronic cardiac rejection. We performed the present study to determine whether AIF-1 was also involved in the inflammatory response associated with human cardiac transplant rejection. AIF-1 gene transcripts were identified by the reverse-transcriptase polymerase chain reaction in endomyocardial biopsy specimens from human heart transplants and in macrophage cell lines. In the 441-base pair coding region of the human and rat cDNAs, the nucleotide sequences were 86% identical and the deduced amino acid sequences were 90% identical. Consistent with our studies in the rat. AIF-1 was selectively expressed in human macrophage-like cell lines, and immunostaining in human heart allografts localized the AIF-1 gene product to a subset of CD68+ macrophages in the interstitial and perivascular spaces. The parallels between rat and human AIF-1 expression suggest that AIF-1 may have a common effect on the function of activated macrophages in cardiac allografts.

Desialylated LDL uptake in human and mouse macrophages can be mediated by a lectin receptor

We have compared the uptake of desialylated low density lipoprotein (LDL) with other modified forms of LDL in mouse peritoneal macrophages and PMA-activated human U937 monocytes. Neuraminidase-treated LDL (NT-LDL) caused significant cholesterol ester accumulation in both cell types, although the efficiency relative to loading with acetylated LDL (AcLDL) was markedly different, suggesting a very different complement of receptors in the cells. We therefore determined the effect of PMA-activation on lipoprotein receptor expression in U937 cells and found that while scavenger receptor concentration was elevated after PMA-activation, there was no significant change in the expression of the LDL receptor. Receptor specificity of NT-LDL uptake was examined by competition experiments using the degradation assay. This showed that 125I-labelled NT-LDL uptake in U937 cells could largely be accounted for by the persistent expression of the LDL receptor in these cells. In contrast, in mouse peritoneal macrophages where LDL receptor expression is very low, 125I-labelled NT-LDL degradation was also effectively competed by asialofetuin. Surprisingly, 125I-labelled NT-LDL degradation was also effectively competed by AcLDL. Measurement of sialic acid content of AcLDL showed that approximately 14% of the LDL sialic acid, equivalent to 2 to 3 residues per particle, was lost during acetylation of LDL with acetic anhydride. Thus competition between 125I-labelled NT-LDL and AcLDL could be due to lectin receptor binding rather than competition for scavenger receptor binding.

Chronic cardiac rejection in the LEW to F344 rat model. Blockade of CD28-B7 costimulation by CTLA4Ig modulates T cell and macrophage activation and attenuates arteriosclerosis

CTLA4Ig, a fusion protein that blocks CD28-B7 costimulation, was studied in a LEW to F344 rat model of chronic cardiac rejection. In rats treated with a single dose of CTLA4Ig (0.5 mg intraperitoneally) 2 d after transplantation, allografts survived significantly longer ( > 70 d in 64%) than in untreated controls or rats treated with control Ig (all rejected within 25 d). Only 25% of grafts from rats treated with a single, high dose of cyclosporine A (25 mg/kg, 2 d after transplantation) survived longer than 70 d. Reverse transcriptase PCR and immunostaining analyses of tissue from 75-d, CTLA4Ig-treated allografts showed reduced expression of the T cell factor IFN-gamma and macrophage activation factors monocyte chemoattractant protein-1, inducible nitric oxide synthase, and galactose/N-acetylgalactosamine macrophage lectin, as well as TGF-beta. Grafts from longterm survivors ( > 120 d) treated with CTLA4Ig showed significant reductions in the frequency and severity of arteriosclerosis in comparison with cyclosporine A-treated rats. Thus, T cell activation is a proximal event in the cascade that culminates in the arteriosclerosis of chronic rejection. Strategies for blocking T cell costimulation may help prevent chronic rejection in clinical transplantation.

Restricted expression of galactose/N-acetylgalactosamine-specific macrophage C-type lectin to connective tissue and to metastatic lesions in mouse lung

We investigated expression of macrophage galactose/N-acetylgalactosamine-specific C-type lectin (MMGL) in normal mouse lung tissue and in lungs with metastatic nodules produced by OV2944-HM-1 mouse metastatic ovarian tumour cells. Cells expressing MMGL were detected in tissue sections using a rat monoclonal antibody (mAB) specific for MMGL, mAb LOM-14. The regions containing cells immunostained using mAb LOM-14 were restricted to the connective tissue surrounding blood vessels and respiratory epithelia, whereas alveolar regions of lung parenchyma were essentially devoid of these cells. In contrast, a significant number of cells in the alveolar regions was shown to express Mac-1 antigen (CD11b/CD18) and leucocyte common antigen (CD45). Immunoelectron microscopic study revealed the presence of MMGL in the intracellular vesicles of cells residing in connective tissue. In the tumour-bearing mice, MMGL-positive cells were also present within metastatic nodules. Their localization outside of the nodules was restricted to connective tissue. Cells with Mac-1 antigens were seen both in the nodules and in the alveolar regions. These results indicate that MMGL serves as a unique macrophage marker in mouse lung tissue due to its topographical site-dependent pattern of expression. The present results also suggest a possible involvement of macrophages expressing MMGL in the immune response directed against metastatic tumour cells.

Upregulation and modulation of inducible nitric oxide synthase in rat cardiac allografts with chronic rejection and transplant arteriosclerosis

BACKGROUND

The Lewis-F344 rat cardiac transplantation model produces cardiac allografts with chronic rejection characterized by arteriosclerotic lesions composed of macrophages and smooth muscle cells. Modulation of the inflammatory response with a diet deficient in essential fatty acids protects against the development of intimal thickening. Little is known about the components of the inflammatory response mediating this process. The cytokine-inducible isoform of nitric oxide synthase (iNOS) regulates the high-output nitric oxide pathway that confers activation properties to macrophages and regulates vasomotion, monocyte adherence, and smooth muscle cell proliferation in the vasculature. The purpose of the present study was to determine whether the iNOS pathway was upregulated during the course of chronic cardiac rejection.

METHODS AND RESULTS

We studied iNOS mRNA and protein expression patterns in a series of Lewis-F344 cardiac allografts with early and late chronic rejection and after modulation of the inflammatory response (in an effort to attenuate arteriosclerosis). Relative gene transcript levels were measured with a 32P-dCTP reverse-transcriptase polymerase chain reaction assay designed to amplify iNOS mRNA. The distribution of the iNOS gene product was examined by immunocytochemistry with a polyclonal antibody against iNOS. NOS transcript levels increased significantly in cardiac allografts (days 7, 14, 28, and 75) compared with paired host hearts (exposed to the same circulation) and syngrafts (P < .003). Immunostaining localized the iNOS antigen within subpopulations of mononuclear inflammatory cells in cardiac allografts--presumably, activated macrophages. The number of iNOS-positive mononuclear cells was 25-fold higher in cardiac allografts compared with paired host hearts and syngrafts (P < .009). In cardiac allografts of 75 days or older, there also was striking iNOS staining within some medial and intimal smooth muscle cells in various vessels. Modulation of the inflammatory response (with a diet deficient in essential fatty acids) produced significant decreases in the intimal thickening score and in the percentage of diseased vessels in 28-day cardiac allografts compared with allografts from rats fed a control diet. There was a correlate decrease in iNOS transcript levels and in the number of iNOS-positive mononuclear cells in the 28-day cardiac allografts from rats fed the essential fatty acid-deficient diet.

CONCLUSIONS

The early and persistent upregulation of iNOS in chronic cardiac rejection and the coincident reduction in arteriosclerosis and downregulation of iNOS suggest that this inducible regulator may contribute to the inflammatory response mediating transplant arteriosclerosis.

Mechanisms of acquired thymic tolerance in experimental autoimmune encephalomyelitis: thymic dendritic-enriched cells induce specific peripheral T cell unresponsiveness in vivo

Experimental autoimmune encephalomyelitis (EAE), an experimental model for the study of multiple sclerosis, is an autoimmune disease of the central nervous system that can be induced in a number of species by immunization with myelin basic protein (MBP). MBP-reactive CD4+ T cells, predominantly expressing the V beta 8.2 T cell receptor (TCR), migrate from the peripheral lymphoid organs and initiate the inflammatory response in the brain. We have previously shown that a single intrathymic injection of MBP or its major encephalitogenic peptide (p71-90), but not a nonencephalitogenic peptide (p21-40), induces antigen-specific systemic tolerance and inhibits the induction of EAE in Lewis rats. In this study, we investigated the mechanisms of induction and maintenance of acquired thymic tolerance in this model. First, we investigated which thymic cell is responsible for "induction" of systemic tolerance. Thymic dendritic-enriched cells, isolated by plastic adherence, when incubated in vitro with p71-90 and injected intravenously into Lewis rats, were capable of preventing the development of EAE, but his protection was lost in thymectomized recipients. In addition, intravenous injection of thymic dendritic cells isolated from animals that had been previously injected intrathymically with p71-90 but not p21-40 also prevented the development of EAE. Second, to determine the "effector" mechanisms involved in acquired thymic tolerance, we compared TCR expression in the brains of animals with actively induced EAE with TCR expression in animals that received intrathymic injection of p71-90 or p21-40. Using a semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) technique, we found increased expression of CD4 and V beta 8.2 message in brains of immunized animals compared with those of naive animals. In animals intrathymically injected with p71-90 but not p21-40, CD4 and V beta 8.2 transcript levels were significantly reduced compared with immunized controls. Immunohistologic studies of brain tissue and spleens with specific V beta 8.2 and control V beta 10 monoclonal antibodies confirmed these observations in vivo. These findings, taken together with recent data demonstrating that activated T cells circulate through the thymus, suggest that interaction of thymic dendritic cells with specific TCR of activated peripheral T cells can lead to inactivation of these antigen-specific cells and confirm the role of V beta 8.2-expressing T cells in EAE.

Detection of a sub-set of polysomal mRNAs associated with modulation of hypusine formation at the G1-S boundary. Proposal of a role for eIF-5A in onset of DNA replication

S phase entry, i.e. start of DNA replication, is a crucial step in proliferation. Inhibition of S phase entry correlates with inhibition of hypusine formation, an event affecting only the eukaryotic initiation factor 5A (eIF-5A). Its hypusine-containing sequence was postulated to authorize polysomal utilization of specific transcripts for proteins necessary to enable DNA replication. Using mimosine to reversibly suppress the hypusine-forming deoxyhypusyl hydroxylase (E.C. 1.14.99.29) in cells while differentially displaying their polysomal versus non-polysomal mRNA populations, we report the detection and classification of several mRNA species that indeed disappear from and reappear at polysomes in concert with inhibition and disinhibition, respectively, of hypusine formation. Based on initial sequence data, two translationally controlled enzymes, both critical for proliferation, are identified as candicate products of such mRNAs, methionine adenosyltransferase (E.C. 2.5.1.6) and cytochrome-c oxidase (EC 1.9.3.1) subunit I. The existence of such putative hypusine-dependent messenger nucleic acids (hymns) provides the basis for a proposal on their molecular function in onset of multiplication.

Cloning and characterization of allograft inflammatory factor-1: a novel macrophage factor identified in rat cardiac allografts with chronic rejection

The development of arteriosclerotic lesions in the Lewis to F344 rat model of chronic cardiac rejection is characterized by macrophage adhesion to the vessel lumen and macrophage infiltration in the neointima prior to smooth muscle cell accumulation. We report the cloning and characterization of allograft inflammatory factor-1 (AIF-1), a novel cDNA that is expressed early and persistently in chronically rejecting cardiac allografts but is absent in cardiac syngrafts and host hearts. The full-length cDNA codes for a hydrophilic polypeptide of 17 kD that contains a 12-amino acid region similar to an EF-hand (calcium-binding) domain. In cardiac allografts AIF-1 transcripts and protein localized to infiltrating mononuclear cells. Analysis of isolated cell populations confirmed that AIF-1 was selectively expressed in macrophages and neutrophils and demonstrated that AIF-1 transcripts could be upregulated by sixfold after stimulation with the T cell-derived cytokine IFN-gamma. Treatment with a diet deficient in essential fatty acids (which attenuates arteriosclerosis) or CTLA-4 Ig (which blocks lymphocyte activation) significantly decreased AIF-1 transcript levels. Upregulation of AIF-1 in the setting of T cell activation suggests that it may play a role in macrophage activation and function.

Up-regulation of endothelin-1 mRNA and peptide expression in rat cardiac allografts with rejection and arteriosclerosis

Acute and chronic rejection are frequent and significant complications of cardiac transplantation, and graft arteriosclerosis is the leading cause of death beyond the first year after transplant. Levels of endothelin-1 (ET-1) are elevated in plasma of patients with cardiac allografts and those with symptomatic vascular atherosclerosis, but little is known about the role of ET-1 in these processes. This study examined intragraft ET-1 expression in rat cardiac models of acute rejection and chronic rejection associated with graft arteriosclerosis. Corrected ET-1 gene transcript levels were measured with a [32P]dCTP reverse transcription polymerase chain reaction assay normalized with glyceraldehyde-3-phosphate dehydrogenase, and the gene product was evaluated by immunohistology with a monospecific anti-ET-1 antibody at different time points after transplant. ET-1 mRNA levels were significantly increased in acutely rejected (Wistar-Furth rat cardiac allografts transplanted into Lewis rat recipients) and chronically rejected (Lewis allografts transplanted into F344 recipients) vascularized cardiac allografts as compared with isograft controls. In acutely rejected allografts, peak expression occurred on day 5 after transplant. In chronically rejected allografts, the increase in ET-1 mRNA was sustained on days 7, 28, and 75. In both acutely and chronically rejected allografts, ET-1 mRNA upregulation was not seen in host spleens or paired host hearts. Immunohistological analysis confirmed that the bulk of ET-1 peptide expression was localized to mononuclear cells that diffusely infiltrated the graft interstitium (acute rejection and early chronic rejection) and accumulated within the neointima of chronically rejecting hearts with arteriosclerosis. These observations, taken together with in vitro data showing that ET-1 production is stimulated by certain cytokines, indicate that the allogeneic stimulus within rejecting vascularized cardiac allografts, presumably cytokine mediated, leads to significant intragraft up-regulation of ET-1 mRNA and peptide expression. The local up-regulation of this vasoactive and mitogenic peptide within acutely and chronically rejected cardiac allografts suggests that ET-1 may be involved in the development of graft arteriosclerosis.

Recent advances in differential display

Differential display and RNA arbitrary primed polmerase chain reaction are methods recently designed to identify and isolate differentially expressed genes. Methodological modifications have since been introduced to streamline the techniques. The major effort has centered on how to eliminate false positives as approached from a variety of angles, ranging from RNA sample preparation, northern blot confirmation, primer length variation, to better experimental design.