BN Rats Research Articles

Combined Effects of Low‐Dose Spironolactone and Captopril Therapy in a Rat Model of Genetic Hypertrophic Cardiomyopathy

The aim of this study was to evaluate the effects of low dose aldosterone antagonist alone or in combination with angiotensin converting enzyme (ACE) inhibitors on the progression of left ventricular dysfunction and remodeling in a congenic rat model of hypertrophic cardiomyopathy. Congenic SS-16BN/Mcwi rats were produced by transfer of chromosome 16 from the BN rat into the salt-sensitive hypertensive (SS/Mcwi) genetic background. The SS-16BN/Mcwi rats developed severe cardiac hypertrophy despite being normotensive even on high salt diet. SS-16BN/Mcwi and SS/Mcwi rats were fed a low salt (0.4% NaCl) diet and treated with either vehicle (CON), spironolactone (20mg/kg per d s.c), captopril (100 mg/kg per d drinking water), or both for four weeks. Echocardiography was performed weekly. Plasma peptide measurements, blood pressure, cardiac fibrosis and heart weight were evaluated at the end of the experimental period. Spironolactone at a low dose had no affect on blood pressure, cardiac fibrosis, heart/body weight ratio and left ventricular wall thickness in either strain. Spironolactone in combination with captopril, decreased the cardiac hypertrophy more than captopril alone. In the SS-16BN/Mcwi rats the combined therapy significantly preserved the cardiac index when compared to control. The study suggests that the addition of low-dose spironolactone to ACE inhibitor treatment prevents the progression of heart hypertrophy independently of blood pressure effects and that combined spironolactone and captopril therapy may be useful in the treatment of hypertrophic cardiomyopathy (Support NIH HL29587, U01 HL66579).

BN phenome: detailed characterization of the cardiovascular, renal, and pulmonary systems of the sequenced rat

The postgenome era has provided resources to link disease phenotypes to the genomic sequence, i.e., creating a disease "phenome." Our detailed characterization of the sequenced BN rat strain (BN/NHsdMcwi) provides the first concerted effort in creating a direct link between a sequenced genome and its resulting biology. For the BN sequence to be of broad value to investigators, these measures need to be put into the context of the spectrum of the laboratory rats, so that their physiology can be benchmarked against the sequenced BN. As a major step in generating a comprehensive cardiovascular and pulmonary disease phenome, we measured 281 traits related to diseases of the heart, lung, and blood (http://pga.mcw.edu) in the sequenced BN. We compared these data with those of the same traits measured across multiple genetic backgrounds, both genders, and differing environments. We show that no single strain, inbred or outbred, can be considered a physiological control strain; what is normal depends on what trait is being measured and the strains' genome backgrounds. We find vast differences between the genders, also dependent on genome background. By combining the values across all strains studied, we generated a "population" mean and normal range of values for each of these traits, which are more genetically representative than the measured values in any single inbred or outbred strain. These data provide a baseline for physiological comparison of traits related to cardiovascular, lung, blood, and renal function in the sequenced BN rats relative to the major strains of rats studied in biomedical research.

Expression of Matrix Metalloproteinase-12 in Persistent Alveolar Macrophage Clusters in Rats with a Chronic Asthma-Like Phenotype

RATIONALE: After experiencing Sendai virus-induced bronchiolitis as weanlings, BN rats develop a chronic postbronchiolitis asthma-like phenotype, characterized by airway obstruction, hyperresponsiveness, inflammation, and remodeling. Because the presence of persistent clusters of alveolar macrophages is pathognomonic for this asthma-like phenotype, we evaluated whether expression of genes related to fibrosis and tissue remodeling, such as matrix metalloproteinase-12 (MMP-12; a metalloelastase expressed by activated macrophages), is elevated in these alveolar macrophage clusters.

Early cytokine profiles in the joint define pathogen clearance and severity of arthritis in Chlamydia‐induced arthritis in rats

Although Chlamydia trachomatis-induced arthritis is among the most common rheumatic diseases having an identified infectious trigger, the pathogenesis of this arthritis is not well defined. We sought to investigate the host-microbe interactions that contribute to the severity of arthritis initiated by chlamydial infection. We established an experimental rat model of C. trachomatis-induced arthritis that recapitulates many pathologic features of the clinical disease. The severity of the arthritis was defined using an established histopathologic scoring system. Host clearance of the pathogen and local cytokine production were examined by enzyme-linked immunosorbent assays. Lewis rats were susceptible to C. trachomatis-induced arthritis, whereas BN rats were relatively resistant to this disease. Significant differences in the histopathologic severity of arthritis were originally observed on day 21, and this prompted an examination of the acute phase of the arthritis. As early as day 5 after the onset of the arthritis, pathologic changes in Lewis rats were more severe than those in BN rats. An evaluation of the role of complement using cobra venom factor treatment excluded complement as being the key to differential sensitivity, because decomplementation did not eliminate the differences in arthritis severity between Lewis and BN rats. Host clearance, in contrast, was significantly different between the rat strains, with BN rats showing more prompt and effective clearance of the pathogen from both synovial tissues and spleen compared with Lewis rats. Local cytokine profiles demonstrated that host resistance was characterized by enhanced synovial expression of tumor necrosis factor alpha, interferon-gamma (IFNgamma), and interleukin-4. These studies demonstrated that cytokines thought to be proinflammatory in nature can play an important role in host defense in infection-triggered arthritis and serve to highlight the dynamic cytokine relationships that constitute effective host-pathogen interactions.

The rat Toxo1 locus directs toxoplasmosis outcome and controls parasite proliferation and spreading by macrophage-dependent mechanisms.

Toxoplasmosis is a healthcare problem in pregnant women and immunocompromised patients. Like humans, rats usually develop a subclinical chronic infection. LEW rats exhibit total resistance to Toxoplasma gondii infection, which is expressed in a dominant mode. A genome-wide search carried out in a cohort of F(2) progeny of susceptible BN and resistant LEW rats led to identify on chromosome 10 a major locus of control, which we called Toxo1. Using reciprocal BN and LEW lines congenic for chromosome 10 genomic regions from the other strain, Toxo1 was found to govern the issue of T. gondii infection whatever the remaining genome. Analyzes of rats characterized by genomic recombination within Toxo1, reduced the interval down to a 1.7-cM region syntenic to human 17p13. In vitro studies showed that the Toxo1-mediated refractoriness to T. gondii infection is associated with the ability of the macrophage to impede the proliferation of the parasite within the parasitophorous vacuole. In contrast, proliferation was observed in fibroblasts whatever the genomic origin of Toxo1. Furthermore, ex vivo studies indicate that macrophage controls parasitic infection spreading by a Toxo1-mediated mechanism. This forward genetics approach should ultimately unravel a major pathway of innate resistance to toxoplasmosis and possibly to other apicomplexan parasitic diseases.

Renal ENaC subunit, Na–K–2Cl and Na–Cl cotransporter abundances in aged, water-restricted F344 × Brown Norway rats

Renal sodium reabsorption is a key determinant of final urine concentration. Our aim was to determine whether differences existed between aged and young rats in their response to water restriction with regard to the regulation of abundance of any of the major distal renal sodium transporter proteins. Male Fisher 344 x Brown Norway (F344 x BN) rats of 3-, 10-, 24-, or 31 months of age (3M, 10M, 24M, or 31M) were either water restricted (WR) for 5 days or control (ad libitum water). Major renal sodium transporters and channel subunits were evaluated by immunoblotting and immunohistochemistry. Age did not significantly affect plasma arginine vasopressin or aldosterone levels, but renin activity was only 8% in 31M-WR rats relative to 3M-WR (P<0.05). Extreme aging (31M) led to decreased outer medullary abundance of the bumetanide-sensitive Na-K-2Cl cotransporter and decreased cortical abundance of the beta- and gamma-subunits (70-kDa band) of the epithelial sodium channel (ENaC) (P<0.05). Water restriction significantly (P<0.05) increased the abundance of Na-K-2Cl cotransporter (NKCC2) and Na-Cl cotransporter (NCC) across ages. However, these increases were significantly blunted as rats aged. Mean band densities were increased in WR rats (relative to age controls) by 54 and 106% at 3M, but only 25 and 29% at 24M and 0 and 6% at 31M for NKCC2 and NCC, respectively. Aged F344 x BN rats have reduced basal distal tubular renal sodium transporter abundances and blunted upregulation during water restriction, which may contribute to decreased urinary concentrating capacity.

Heart Allograft Protection with Low-Dose Carbon Monoxide Inhalation: Effects on Inflammatory Mediators and Alloreactive T-cell Responses

Carbon monoxide (CO), a byproduct of heme catalysis, has lately received considerable attention as a regulatory molecule in cellular and biological processes. CO has been shown to provide potent protection against a variety of tissue injuries. We hypothesized in this study that low concentration CO would be beneficial for organ allografts, which frequently undergo several types of injury such as ischemia/reperfusion, alloimmune reaction, and inflammation The efficacy of low-dose CO was examined in a fully allogeneic LEW to BN rat heterotopic heart transplantation (HHTx) model. Recipients were kept in air or exposed to low-dose CO (20 ppm) for 14, 28, or 100 days after HHTx under short-course tacrolimus CO treatment (d0-28, 0-100) was remarkably effective in prolonging heart allograft survival to a median of >100 from 45 days in the air-control group, with significant reductions of arteritis, fibrosis, and cellular infiltration, including macrophages and T cells. CO inhibited intragraft upregulation of Th1 type cytokines (IL-2, IFNgamma), proinflammatory mediators (IL-1beta, TNFalpha, IL-6, COX-2), and adhesion molecule. Shorter CO exposure in early (0-13d) and late (14-28d) posttransplant periods also prolonged graft survival, with a significant inhibition of inflammatory mediators These results show that low dose CO inhalation protects heart allografts and can considerably prolong their survival. CO appears to function via multiple mechanisms, including direct inhibition of Th1 type cytokine production and regulation of inflammatory responses.

Angiogenesis and capillary maturation phenotypes associated with the Edpm3 locus on rat chromosome 3

The quantitative trait locus (QTL) Edpm3 is one of a group of additively acting QTL \responsible for the difference in estrogen-induced pituitary tumor growth between the tumor-susceptible F344 and tumor-resistant BN rat strains. The F344.BN-Edpm3(BN) rat strain was produced by moving the segment of rat Chr 3 between D3Mgh7 and D3Mgh13, which contains the Edpm3 QTL, from the BN strain into the F344 genetic background. In a previous study, we used this congenic line to find that the BN allele of the Edpm3 QTL reduces tissue mass and S-phase fraction in the estrogen-induced rat pituitary tumor. We now report on the use of this congenic line to investigate the linkage of Edpm3 to tumor angiogenesis. Contrary to expectation, the F344.BN-Edpm3(BN) strain has significantly greater angiogenic activity than does F344 in both treated and untreated rats. Microvessel count (MVC), perivascular space, and number of nonattached pericytes/pericapillary fibroblasts are all elevated in the pituitary by chronic estrogen treatment and their values are significantly greater in F344.BN-Edpm3(BN) than F344. Thus, although there is greater angiogenic activity in the pituitary of estrogen-treated F344.BN-Edpm3(BN) rats, there is a deficiency in capillary maturation compared with F344.

Consequences of blood loss on growth of artificial metastases.

Previous studies have shown that lung metastases from a nonimmunogenic sarcoma (LS175) in BN (homozygous for RTln) rats were stimulated by blood transfusions. Enhanced growth was also observed after abdominal surgery combined with allogeneic blood transfusions while syngeneic blood transfusions had no effect. These experimental findings have been confirmed in retrospective clinical studies. The allogeneic blood transfusion effect may be avoided in cancer patients by autologous blood transfusions although this implies blood donation before surgery. The aim of the present study was to investigate the effect of blood loss before surgery on formation ('take') of lung colonies, and on the outgrowth of established metastases in the BN rat model. These aspects of tumour behaviour were also investigated in rats undergoing surgery, or receiving blood transfusion, or both, after blood loss. The results indicate that blood loss has a profound stimulating effect on the growth of established metastases, but not on the 'take' of tumour cells. This stimulating effect was also present when blood loss was combined with surgery, while previously surgery alone was found to have no effect. Allogeneic and syngeneic transfusions in combination with blood loss both had a strong stimulating effect on growth of established lung metastases. The results indicate that blood loss may be an important factor in determining the outcome of metastatic growth.

Synergistic antitumour effect of recombinant human tumour necrosis factor alpha with melphalan in isolated limb perfusion in the rat.

The efficacy of isolated limb perfusion (ILP) for 'intransit' metastases from malignant melanoma and irresectable soft tissue sarcoma has been improved considerably by the addition of tumour necrosis factor (TNF) alpha. A rat sarcoma tumour model was, therefore, developed to evaluate the effects of TNF-alpha, melphalan and the combination of these drugs in the treatment of sarcoma. In BN rats bearing the non-immunogenic BN 175 sarcoma ILPs were performed with perfusate only, TNF-alpha, melphalan alone, or in combination when tumours had grown to approximately 1.5 cm in diameter. All rats treated with sham perfusion or perfusion with 50 micrograms TNF-alpha showed progressive disease. After perfusion with 40 micrograms melphalan no change in tumour diameter was observed in any rats at 4 days. After a combined perfusion with 40 micrograms melphalan and 50 micrograms TNF-alpha complete remission was noted in 12 of 16 rats. This synergistic effect in vivo between relatively ineffective doses of TNF-alpha and melphalan was not observed in vitro.

Effect of FTY720 in Rat Small Bowel Transplantation: Expression of Mucosal Addressin Cell Adhesion Molecule-1

Aim Mucosal addressin cell adhesion molecule-1 (MAdCAM-1) mediates the homing of lymphocytes to gut-associated tissues (GALT). We performed a semiquantitative analysis of MAdCAM-1 expression during small bowel graft rejection in rat treated with FTY720. Methods Orthotopic small bowel transplantations (SBT) were performed from BN rats to LEW rats. Isografted animals served as controls. Three groups of SBT animals were studied on days 3, 5, 7 after operations (Isograft, untreated allograft, allograft with FTY720). FTY720 was orally administered by gavage (1 mg/kg/d) to allograft models on 7 consecutive days. Cryostat sections were prepared from grafts, including Peyer’s patches (PPs). Indirect immunoperoxidase staining was performed using mAbs against MAdCAM-1. The degree of vascular endothelial staining on high endothelial venules (HEV) in the PPs was graded from 1 (low levels) to 5 (high levels), and in the vessels of the lamina propia from 1 (faint), to 2 (low at the base of villi), 3 (low to the middle of villi), 4 (high to the middle of villi), to 5 (high to villi tip). Results The graft survival was prolonged in the FTY720-treated group. MAdCAM-1 expression on HEVs in PPs was down-regulated during rejection. In contrast its expression on endothelial cells of vessels in the lamina propria was up-regulated during rejection. In the FTY720-treated groups, MAdCAM-1 expression on HEVs in PPs was up-regulated and its expression on endothelial cells of vessels in the lamina propria was down-regulated compared with untreated allograft group. Conclusions Alteration in MAdCAM-1 expression may be associated with the development of SB graft rejection. The vessels at the base of villi, which are associated with lymphocyte recruitment, may become sites of intestine immune reactivity during the early phase of small bowel allograft rejection. FTY720 was found to prevent the down-regulation of MAdCAM-1 expression on HEVs in PPs and the up-regulation of its expression on endothelial cells of vessels in the lamina propria while also prolonging small bowel allograft survival.

Transfection of CD40Ig Into Liver Prevents Acute Rejection in Rat Liver Transplantation

Objective To investigate the effect of CD40Ig upon acute rejection of rat liver transplants. Methods Thirty-two orthotopic liver transplants were performed using Lewis to BN rats with “the two-cuff technique”. The rats were randomly divided into three groups. Group A served as controls ( n = 10); group B ( n = 11) and group C ( n = 11); Lipofectamine2000-pcDNA3.1 or Lipofectamine2000-pcDNA3.1. CD40Ig complex was injected into Lewis portal vein ex vivo before cold storage of the liver. On the fifth day after transplantation, three rats in each group were killed to study the pathological changes and TUNEL immune histochemistry performed to examine CD40Ig expression. Lymphocytes were obtained from the spleen. The mixed lymphocyte reaction (MLR) was performed to determine tolerance and sheep anti-human immunoglobulin G (IgG)-FITC-labeled T cells counted by flow cytometry. Postoperative survival times of rats in each group were recorded. The pathological changes of dead rats were observed. Results The mean survival times of group A and B were 11.00 ± 4.28 and 12.75 ± 5.57 days, respectively. There were serious acute rejections in allograft liver in groups A and B. Apoptosis index was 33.67 ± 5.69 versus 39.00 ± 5.29. Group C mean survival time was 41.25 ± 13.70 days ( P < .01). Immune histochemistry showed CD40Ig-positive elements in the allograft liver, which revealed light acute rejection and apoptosis index was 0.27 ± 0.21 ( P < .01). The part of the allografted liver in a dead rat showed light acute rejection while the others displayed chronic rejection. Recipients were specifically tolerant to donors in the MLR assay. The IgG-FITC-labeled T cells accounted for 11.57% of all T cells in group C. Conclusions CD40Ig transfection inhibited T-cell costimulatory pathway, prevented acute rejection, and prolonged graft survival.

Effect of hypertension on angiotensin-(1–7) levels in rats with different angiotensin-I converting enzyme polymorphism

To determine circulating angiotensin-(1–7) [Ang-(1,7)] levels in rats with different angiotensin converting enzyme (ACE) genotypes and to evaluate the effect of hypertension on levels of this heptapeptide, plasma levels of angiotensin II (Ang II) and Ang-(1–7) were determined by HPLC and radioimmunoassay in (a) normotensive F 0 and F 2 homozygous Brown Norway (BN; with high ACE) or Lewis (with low ACE) rats and (b) in hypertensive F 2 homozygous male rats (Goldblatt model). Genotypes were characterized by PCR and plasma ACE activity measured by fluorimetry. Plasma ACE activity was 2-fold higher ( p < 0.05) in homozygous BN compared to homozygous Lewis groups. In the Goldblatt groups, a similar degree of hypertension and left ventricular hypertrophy was observed in rats with both genotypes. Plasma Ang II levels were between 300–400% higher ( p < 0.05) in the BN than in the Lewis rats, without increment in the hypertensive animals. Plasma Ang-(1–7) levels were 75–87% lower in the BN rats ( p < 0.05) and they were significantly higher ( p < 0.05) in the hypertensive rats from both genotypes. Plasma levels of Ang II and Ang-(1–7) levels were inversely correlated in the normotensive rats (r = − 0.64; p < 0.001), but not in the hypertensive animals. We conclude that there is an inverse relationship between circulating levels of Ang II and Ang-(1–7) in rats determined by the ACE gene polymorphism. This inverse relation is due to genetically determined higher ACE activity. Besides, plasma levels of Ang-(1–7) increase in renovascular hypertension.

Rat strains differ in antibody response to natural Haemophilus species infection

Antibody response to Haemophilus species in rat strains was monitored by enzyme-linked immunosorbent assay (ELISA) using antigens of two Haemophilus strains and a Pasteurella pneumotropica strain. Five rat strains from a breeding colony naturally infected by Haemophilus were significantly different in ELISA antibody activity and in the number of seropositive animals. BN and RP rats were (relatively) high and low responders, respectively and BUF, LEW and WAG rats were intermediate. In a second study, five rat strains were exposed to Haemophilus-infected rats, and, after six weeks, were also significantly different in ELISA antibody activity and in numbers of seropositive animals. Here, BN and LEW rats were (relatively) high and low responders, respectively, and BD IX, F344 and WKY rats were intermediate.

Nest-building behaviour in male rats from three inbred strains: BN/HsdCpb, BDIX/Or1Ico and LEW/Mol

AbstractThree inbred strains of male laboratory rat (BN/HsdCpb, BDIX/Or1Ico and LEW/Mol) were provided with nest boxes and nest materials, and were observed for nest-building activity. After 7 days, each cage and nest box was examined. Each nest was weighed and scored for complexity, and returned to the cage. This was repeated after a further 7 days and the nest removed completely. This routine was repeated three times. All three strains of rat built nests inside the nest box and showed the same stages of construction. There was a significant increase in nest complexity between day 7 and day 14 in the strains BN and BDIX. Furthermore, BDIX rats used significantly more material for the nests, compared with the BN and LEW rats. In a second experiment, using the same rats, nest material was offered in four different ways. LEW rats used nesting material irrespective of where it was placed; BN rats only used straw placed on the top of the cage when no alternative was provided in the cage, and would not use the nest box roof when it was covered with bedding; whereas BDIX rats would only use nest material placed within the cage and would not use straw placed on the cage lid. BN rats also used nest material to cover the entrance to the nest box, a practice not carried out by the other strains. This study demonstrates that these rat strains have retained their natural nest-building behaviour. We suggest that the correct stimuli must be provided in order for this behaviour to be exhibited; in addition, the way in which the nest materials are provided must be in accordance with strain-specific characteristics.

Eae19, a New Locus on Rat Chromosome 15 Regulating Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) and its animal model, myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (MOG-EAE), share a complex genetic predisposition with contributions from the major histocompatibility complex class II genes and many other genes. Linkage mapping in F(2) crosses between the susceptible DA rat strain and the resistant ACI or BN rat strains in various models of autoimmune neuroinflammation have repeatedly displayed suggestive linkage to a region on rat chromosome 15. A direct study of this region was undertaken in congenic strains by transferring resistant ACI alleles to the susceptible DA background. Phenotypic analysis demonstrated lower maximal and cumulative EAE scores in the DA.ACI-D15Rat6-D15Rat71 (C15), DA.ACI-D15Rat6-D15Rat48, D15Rat126-D15Rat71 (C15R3b), and DA.ACI-D15Rat23-D15rat71 (C15R4) strains compared to the parental DA rat strain. Linkage analysis was then performed in a (DA x PVG.AV1)F(7) advanced intercross line, resulting in a LOD score of 4.7 for the maximal EAE score phenotype at the peak marker D15Rat71 and a confidence interval of 13 Mb, overlapping with the congenic fragment defined by the C15R3b and the C15R4 strains. Thus, a new MOG-EAE locus with the designation Eae19 is identified on rat chromosome 15. There are 32 confirmed or predicted genes in the confidence interval, including immune-responsive gene 1 and neuronal ceroid lipofuscinose gene 5. Definition of loci such as Eae19 enables the characterization of genetically regulated, evolutionary conserved disease pathways in complex neuroinflammatory diseases.

Leptin resistance exacerbates diet-induced obesity and is associated with diminished maximal leptin signalling capacity in rats

Leptin resistance is generally considered a consequence of obesity. We postulated that leptin resistance is associated with diminished hypothalamic leptin signalling capacity and that leptin resistance is causal to obesity. We assessed maximal leptin-mediated binding of the transcription factor signal transducer and activator of transcription 3 (STAT3), and the response to high-fat feeding in lean leptin-resistant rats. Recombinant adeno-associated virus encoding rat leptin cDNA (rAAV-leptin) or control vector were administered by intracerebroventricular injection to lean F344 x BN rats for up to 150 days, and food consumption, body weight, serum leptin and glucose tolerance were measured. Leptin-mediated hypothalamic transcription factor binding was assessed at day 150 following an intracerebroventricular injection of 2 mug leptin. Rats pretreated with either control or rAAV-leptin vector for 94 days were given a high-fat diet, and energy intake, body weight gain and adiposity were examined. The rAAV-leptin-treated rats initially responded to leptin gene delivery then became leptin-resistant. They displayed persistent submaximal hypothalamic leptin signalling and enhanced insulin sensitivity, yet maximal hypothalamic signalling capacity was decreased by more than 50%. On a high-fat diet, the leptin-resistant rats consumed more energy, gained more weight and accumulated greater visceral fat mass than controls. The maximal hypothalamic leptin signalling capacity was diminished in leptin-resistant rats receiving central rAAV-leptin gene therapy. Moreover, this leptin-invoked leptin resistance perturbs the regulation of energy homeostasis in response to high fat exposure, producing augmented energy consumption. This, coupled with potential hypersensitivity to insulin, creates a milieu favouring fat deposition. Our data suggest that leptin resistance is both a consequence and cause of obesity.

Existence of no-observed effect levels for 2-amino-3,8-dimethylimidazo[4,5- f]quinoxaline on hepatic preneoplastic lesion development in BN rats

There is increasing evidence that dose–response curve of genotoxic carcinogen is nonlinear and a practical threshold dose exists. However, little is known about differences in the dose–response relationship of genotoxic carcinogen among different strain rats. Herein, we showed that low doses of genotoxic carcinogen 2-amino-3,8-dimethylimidazo[4,5- f] quinoxaline (MeIQx) had no effects on induction of liver glutathione S-transferase placental form (GST-P)-positive foci in both BN and F344 rats, and therefore demonstrated the existence of no-observed effect level for hepatocarcinogenicity of this genotoxic carcinogen irrespective of strains. These findings further support our notion that a practical threshold dose for MeIQx hepatocarcinogenicity exists in rats.

Two Structurally Related Rat Ly49 Receptors with Opposing Functions (Ly49 Stimulatory Receptor 5 and Ly49 Inhibitory Receptor 5) Recognize Nonclassical MHC Class Ib-Encoded Target Ligands

The Ly49 family of lectin-like receptors in rodents includes both stimulatory and inhibitory members. Although NK alloreactivity in mice is regulated primarily by inhibitory Ly49 receptors, in rats activating Ly49 receptors are equally important. Previous studies have suggested that activating rat Ly49 receptors are triggered by polymorphic ligands encoded within the nonclassical class Ib region of the rat MHC, RT1-CE/N/M, while inhibitory Ly49 receptors bind to widely expressed classical class Ia molecules encoded from the RT1-A region. To further investigate rat Ly49-mediated regulation of NK alloreactivity, we report in this study the identification and characterization of two novel paired Ly49 receptors that we have termed Ly49 inhibitory receptor 5 (Ly49i5) and Ly49 stimulatory receptor 5 (Ly49s5). Using a new mAb (mAb Fly5), we showed that Ly49i5 is an inhibitory receptor that recognizes ligands encoded within the class Ib region of the u and l haplotypes, while the structurally related Ly49s5 is an activating receptor that recognizes class Ib ligands of the u haplotype. Ly49s5 is functionally expressed in the high NK-alloresponder PVG strain, but not in the low alloresponder BN strain, in which it is a pseudogene. Ly49s5 is hence not responsible for the striking anti-u NK alloresponse previously described in BN rats (haplotype n), which results from repeated alloimmunizations with u haplotype cells. The present studies support the notion of a complex regulation of rat NK alloreactivity by activating and inhibitory Ly49 members, which may be highly homologous in the extracellular region and bind similar class Ib-encoded target ligands.

Altered trafficking of cells during acute pulmonary allergic and viral inflammatory stimuli in rats with the chronic postbronchiolitis asthma-like phenotype

and Viral Inflammatory Stimuli in Rats With the Chronic Postbronchiolitis Asthma-Like Phenotype R. L. SORKNESS1, L. A. ROSENTHAL2, T. PIER2, S. P. AMINEVA2, R. J. SZAKALY2, R. F. LEMANSKE, Jr.3; 1Sch of pharmacy, UNIVERSITY OF WISCONSIN, Madison, WI, 2Medicine, UNIVERSITY OF WISCONSIN, Madison, WI, 3Pediatrics, UNIVERSITY OF WISCONSIN, Madison, WI. RATIONALE: Airway inflammation in asthma may be due to enhanced vulnerability of airways to common inflammatory stimuli. We hypothesized that rats with chronic airway dysfunction would differ from normals in their acute pulmonary inflammatory responses. METHODS: Normal BN rats were compared with asthma-like BN rats that were >10wks post early age bronchiolitis. Acute allergic inflammation was induced by a single exposure to aerosolized ragweed pollen extract 2wks after sensitization, and evaluated at 1 or 7 days; viral inflammation was induced with a tracheal insufflation of attenuated mengovirus, and evaluated in 3 days. Airspace infiltrates were quantified with bronchoalveolar lavage (BAL), and airway wall eosinophils (eos) with staining of major basic protein (MBP) in lung sections. RESULTS: Unchallenged normal and asthma-like rats did not differ significantly with regard to BAL eos or airway MBP. However, the asthmalike rats had significantly greater airway wall MBP (p=0.001) and fewer BAL eos (p=0.02) 1 day after allergen challenge, and fewer BAL eos (p=0.04) with similar airway MBP 7 days after allergen. During viral infection a similar pattern occurred, the asthma-like rats having few eos and neutrophils in BAL (p<0.04), but present in lung sections. BAL viral titers were similar in the 2 groups. CONCLUSION: During acute inflammation the asthma-like rats have fewer eos present in the airspace, but equal or greater numbers in airway walls, compared with normals. These data are consistent with the hypothesis that asthmatic airways exhibit different patterns of inflammatory cell trafficking that result in greater vulnerability of the airways to allergic or viral insults. J ALLERGY CLIN IMMUNOL Abstracts S47 VOLUME 115, NUMBER 2