CNTO 530: molecular pharmacology in human UT-7EPO cells and pharmacokinetics and pharmacodynamics in mice.

CNTO 530 is a 58 kD antibody Fc domain fusion protein, created using Centocor's MIMETIBODY platform, that contains two EMP1 sequences as a pharmacophore. CNTO 530 has no sequence homology with EPO but acts as a novel erythropoietin receptor agonist. In UT-7(EPO) cells, CNTO 530 caused protein phosporylation of the erythropoietin receptor associated signaling pathway (Jak2, STAT5, AKT and ERK1/2). CNTO 530 also rescued these cells from apoptosis and mediated proliferation. In mice, pharmacokinetic analysis showed that CNTO 530 was slowly cleared from circulation with a t(1/2) approximately 40 h. Pharmacodynamic analysis in mice showed that a single sc dose of CNTO 530 caused a long-lived stimulation of erythropoiesis that translated into increases in red blood cell counts and hemoglobin values that were maintained for at least 28 d. In conclusion, CNTO 530 is a long-lived EPO-R agonist that stimulates erythropoiesis in a manner similar to epoetin-alpha. These data suggest that CNTO 530 may be an effective treatment of anemia in humans.

Expression of human tissue factor under the control of the mouse tissue factor promoter mediates normal hemostasis in knock-in mice.

BACKGROUND: Tissue factor (TF) is expressed widely at the subluminal surface of blood vessels and serves as the primary cellular initiator of the extrinsic pathway of blood coagulation. Lack of TF in mice resulted in lethality in utero, but human TF (huTF) expressed at low levels from a human minigene rescued null mice from prenatal death. Although these low-TF expressing transgenic mice developed to term, they had a significantly shorter life span and exhibited hemorrhage and fibrosis in the heart. METHODS: Human TF knock-in (TFKI) mice were generated by replacing the first two exons of the mouse (murine) TF (muTF) gene with the huTF complete coding sequence, thus placing it under the control of the endogenous muTF promoter. RESULTS: Expression of huTF in the TFKI mice was similar to muTF in wild-type (wt) mice. The TFKI mice showed no microscopic evidence of spontaneous hemorrhage in the heart, nor cardiac fibrosis at up to 18 months of age. Immunohistochemistry showed that huTF was expressed in cells surrounding blood vessels in TFKI mice. Coagulation activity of brain homogenates from TFKI mice was comparable with that from wt brain. Cardiac hemorrhage similar to that of the low-TF transgenic mice occurred in the TFKI mice when huTF was blocked by a neutralizing anti-huTF monoclonal antibody. CONCLUSION: We generated a transgenic mouse line that expresses huTF under the control of the endogenous muTF promoter at physiological levels. Our results suggest that huTF can fully reconstitute the murine coagulation system and mediate normal hemostasis.

Practical aspects of including functional endpoints in developmental toxicity studies. Case study: immune function in HuCD4 transgenic mice exposed to anti-CD4 MAb in utero.

Keliximab is a human-cynomolgus monkey chimeric (Primatized) monoclonal antibody with specificity for human and chimpanzee CD4. As the preclinical safety assessment of biopharmaceuticals requires evaluation in pharmacologically responsive species, comprehensive toxicology studies, including reproductive toxicity, of this antibody were conducted in a human CD4 transgenic mouse model. The reproductive toxicology studies included a pre- and postnatal development study that incorporated immunotoxicological evaluation of offspring (F1) mice. The potential effects of exposure to treating maternal mice (F0) with keliximab during pregnancy and lactation on offspring viability, physical growth, neurobehavioral development, reproductive function, lymphoid tissue morphological structure, lymphocyte subsets and host resistance to Candida albicans infection were assessed. The results showed no impairment of these functions. The use of F1 transgenic mice in study with keliximab provides an example of a novel practical approach to assess developmental immunotoxicity within a study of pre- and postnatal development designed in accordance with ICH Guidelines.

Preclinical efficacy and safety of mepolizumab (SB-240563), a humanized monoclonal antibody to IL-5, in cynomolgus monkeys.

BACKGROUND: Allergic respiratory diseases are characterized by large numbers of eosinophils and their reactive products in airways and blood; these are believed to be involved in progressive airway damage and remodeling. IL-5 is the principal cytokine for eosinophil maturation, differentiation, and survival. Mepolizumab (SB-240563), a humanized monoclonal antibody (mAb) specific for human IL-5, is currently in clinical trials for treatment of asthma. OBJECTIVE: The purpose of this study was to characterize the pharmacologic activity and long-term safety profile of an anti--human IL-5 mAb to support clinical trials in asthmatic patients. METHODS: Naive and Ascaris suum -sensitive cynomolgus monkeys received various dose levels of mepolizumab and were monitored for acute and chronic pharmacologic and toxic responses. RESULTS: To support preclinical safety assessment, cynomolgus monkey IL-5 was cloned, expressed, and characterized. Although monkey IL-5 differs from human IL-5 by 2 amino acids (Ala27Gly and Asn40His), mepolizumab has comparable inhibitory activity against both monkey IL-5 and human IL-5. In A suum--sensitive monkeys, single doses of mepolizumab significantly reduced blood eosinophilia, eosinophil migration into lung airways, and levels of RANTES and IL-6 in lungs for 6 weeks. However, mepolizumab did not affect acute bronchoconstrictive responses to inhaled A suum. In an IL-2--induced eosinophilia model (up to 50% blood eosinophilia), 0.5 mg/kg mepolizumab blocked eosinophilia by >80%. Single-dose and chronic (6 monthly doses) intravenous and subcutaneous toxicity studies in naive monkeys found no target organ toxicity or immunotoxicity up to 300 mg/kg. Monkeys did not generate anti-human IgG antibodies. Monthly mepolizumab doses greater than 5 mg/kg caused an 80% to 100% decrease in blood and bronchoalveolar lavage eosinophils lasting 2 months after dosing, and there was no effect on eosinophil precursors in bone marrow after 6 months of treatment. Eosinophil decreases correlated with mepolizumab plasma concentrations (half-life = 13 days). CONCLUSION: These studies demonstrate that chronic antagonism of IL-5 by mepolizumab in monkeys is safe and has the potential, through long-term reductions in circulating and tissue-resident eosinophils, to be beneficial therapy for chronic inflammatory respiratory diseases.

Comparison of adipose tissue changes following administration of rosiglitazone in the dog and rat.

Rosiglitazone (BRL-49653-C), a thiazolidinedione, is a potent agonist for the nuclear hormone receptor peroxisome proliferator-activated receptor gamma (PPARgamma). Thiazolidinediones have been reported to induce adipocyte differentiation in vitro and there is limited data on their effects in vivo. The objective of this study was to compare the effects of rosiglitazone on adipocyte differentiation between dogs and rats. Morphological (light and ultrastructural) and morphometric evaluations were conducted on perirenal adipose tissue from dogs that have been treated for 1 month with 0.4, 5, 60 mg/kg/day and rats treated for the same period with 80 mg/kg/day. There was a dose-related change in the phenotype of white adipose tissue in dogs, reflected by an increase in nuclear numerical density (up to threefold) and cytoplasmic area fraction (up to 2.1-fold). In addition, there was an enlargement of the nuclei and a reduction in the size of the white adipocyte lipid vacuoles. Ultrastructural changes included an increase in the number of mitochondria per adipocyte. In the rat, similar changes were seen in nuclear numerical density (1.5-fold increase) and cytoplasmic area fraction (2.2-fold increase). There were also increased numbers of mitochondria per cell in white adipocytes giving them similar numbers of mitochondria to brown adipocytes. In the brown adipocytes, there was a reduction in cytoplasmic area fraction with a corresponding increase in the size of the lipid filled vacuoles in other words there was a converging of the phenotypes of the white and brown adipose tissues.

Immunomodulatory effects of anti-CD4 antibody in host resistance against infections and tumors in human CD4 transgenic mice.

Anti-CD4 antibodies, which cause CD4(+) T-cell depletion, have been shown to increase susceptibility to infections in mice. Thus, development of anti-CD4 antibodies for clinical use raises potential concerns about suppression of host defense mechanisms against pathogens and tumors. The anti-human CD4 antibody keliximab, which binds only human and chimpanzee CD4, has been evaluated in host defense models using murine CD4 knockout-human CD4 transgenic (HuCD4/Tg) mice. In these mice, depletion of CD4(+) T cells by keliximab was associated with inhibition of anti-Pneumocystis carinii and anti-Candida albicans antibody responses and rendered HuCD4/Tg mice susceptible to P. carinii, a CD4-dependent pathogen, but did not compromise host defense against C. albicans infection. Treatment of HuCD4/Tg mice with corticosteroids impaired host immune responses and decreased survival for both infections. Resistance to experimental B16 melanoma metastases was not affected by treatment with keliximab, in contrast to an increase in tumor colonization caused by anti-T cell Thy1.2 and anti-asialo GM-1 antibodies. These data suggest an immunomodulatory rather than an overt immunosuppressive activity of keliximab. This was further demonstrated by the differential effect of keliximab on type 1 and type 2 cytokine expression in splenocytes stimulated ex vivo. Keliximab caused an initial up-regulation of interleukin-2 (IL-2) and gamma interferon, followed by transient down-regulation of IL-4 and IL-10. Taken together, the effects of keliximab in HuCD4/Tg mice suggest that in addition to depleting circulating CD4(+) T lymphocytes, keliximab has the capability of modulating the function of the remaining cells without causing general immunosuppression. Therefore, keliximab therapy may be beneficial in controlling certain autoimmune diseases.

Maximization of signal derived from cDNA microarrays.

Microarray technology is a powerful tool for generating expression data on a large number of genes simultaneously. However, as for any assay, it must be reproducible to give confidence in the results. Using a classical statistical method--the factorial design of experiments--we have assessed the effects of different experimental factors in our system. Significant effects on signal were seen when the standard components were substituted with a different enzyme, fluorescent label, or RNA purification method. This has led to the implementation of an improved procedure that maximizes signal without affecting the variability of the system, thus increasing the signal-to-noise ratio. In addition, we were able to quantify the variability between microarrays and replicates within microarrays.

Modification of the Fc region of a primatized IgG antibody to human CD4 retains its ability to modulate CD4 receptors but does not deplete CD4(+) T cells in chimpanzees.

Keliximab, a Primatized IgG1 CD4 mAb, was reconfigured to an IgG4 antibody. The gamma4 constant region was further modified by substituting glutamic acid for serine at position 235 in the CH2 domain (IgG4-E), to remove residual binding to Fcgamma receptors, and substitution of serine with proline at position 228 in the hinge region (IgG4-PE) for greater stability. Pharmacokinetic analysis in rats gave a t(1/2) of approximately 4 days for IgG4-E and 9 days for IgG4-PE, consistent with a greater stability of the IgG4-PE molecule. The effects on T cell subsets were assessed in chimpanzees given escalating doses of IgG4-PE: 0.05 mg/kg on Day 16, 1.5 mg/kg dose on Day 43, and 15 mg/kg on Day 85. Receptor modulation was observed at the two highest doses, but no depletion of T cells at any dose. The in vitro and in vivo results demonstrate the potential of this IgG4-PE mAb for use in human trials.

Preclinical development of keliximab, a Primatized anti-CD4 monoclonal antibody, in human CD4 transgenic mice: characterization of the model and safety studies.

The preclinical safety assessment of biopharmaceuticals necessitates that studies be conducted in species in which the products are pharmacologically active. Monoclonal antibodies are a promising class of biopharmaceuticals for many disease indications; however, by design, these agents tend to have limited species cross-reactivity and tend to only be active in primates. Keliximab is a human-cynomolgus monkey chimeric (Primatized) monoclonal antibody with specificity for human and chimpanzee CD4. In order to conduct a comprehensive preclinical safety assessment of this antibody to support chronic treatment of rheumatoid arthritis in patients, a human CD4 transgenic mouse was used for chronic and reproductive toxicity studies and for genotoxic studies. In addition, immunotoxicity studies were conducted in these mice with Candida albicans, Pneumocystis carinii and B16 melanoma cells to assess the effects of keliximab on host resistance to infection and immunosurveillance to neoplasia. The results of these studies found keliximab to be well tolerated with the only effects observed being related to its pharmacologic activity on CD4+ T lymphocytes. The use of transgenic mice expressing human proteins provides a useful alternative to studies in chimpanzees with biopharmaceutical agents having limited species cross-reactivity.

Repeated acetaminophen dosing in rats: adaptation of hepatic antioxidant system.

Repeated dosing of acetaminophen (paracetamol) to rats is reported to decrease their sensitivity to its hepatotoxic effects, which are associated with oxidative stress and glutathione depletion. We determined if repeated acetaminophen dosing produced adaptive response of key antioxidant system enzymes. Male rats (Sprague-Dawley, 10 weeks) were given 800, 1200, or 1600 mg/kg/day acetaminophen by oral gavage for 4 days. Liver was assayed for oxidative stress and antioxidant markers: malondialdehyde (MDA), thiobarbituric acid reactive substance (TBARS), total antioxidant status (TAS), glutathione (GSH), glutathione reductase (GR), glutathione peroxidase (GPx), glucose-6-phosphate dehydrogenase (G6PD), catalase (CAT), and superoxide dismutase (SOD), and alanine transaminase (ALT) as a marker of hepatocellular injury. Acetaminophen at 1200/1600 mg/kg decreased GSH 26/47%, GPx 21/26%, CAT 35/28%, SOD 21/12%; and TAS 28/18% (correlated with CAT, r=0.91; SOD, r=0.66; GPx, r=0.45). Despite antioxidant deficiencies, and no TBARS change, MDA decreased 26%/33%/37% at 800/1200/1600 mg/kg, which correlated with increased GR (61%/62%/76%, r=0.77) and G6PD (130%/110%/190%, r=0.78). Both MDA (r=0.68) and G6PD (r=0.71) correlated with hepatic ALT, which decreased 27%/43%/48%, respectively. Resistance to acetaminophen hepatotoxicity produced by repeated exposure is partially attributable to upregulation of hepatic G6PD and GR activity as an adaptive and protective response to oxidative stress and glutathione depletion.

A strategy for primary high throughput cytotoxicity screening in pharmaceutical toxicology.

PURPOSE: Recent advances in combinatorial chemistry and high throughput screens for pharmacologic activity have created an increasing demand for in vitro high throughput screens for toxicological evaluation in the early phases of drug discovery. METHODS: To develop a strategy for such a screen, we have conducted a data mining study of the National Cancer Institute's Developmental Therapeutics Program (DTP) cytotoxicity database. RESULTS: Using hierarchical cluster analysis, we confirmed that the different tissues of origin and individual cell lines showed differential sensitivity to compounds in the DTP Standard Agents database. Surprisingly, however, approaching the data globally, linear regression analysis showed that the differences were relatively minor. Comparison with the literature on acute toxicity in mice showed that the predictive power of growth inhibition was marginally superior to that of cell death. CONCLUSIONS: This datamining study suggests that in designing a strategy for high throughput cytotoxicity screening: a single cell line, the choice of which may not be critical, can be used as a primary screen; a single end point may be an adequate measure and a cut off value for 50% growth inhibition between 10(-6) and 10(-8) M may be a reasonable starting point for accepting a cytotoxic compound for scale up and further study.

Selective inhibition of phospholipases by atiprimod, a macrophage targeting antiarthritic compound.

Azaspiranes are cationic amphiphilic compounds that are active in a number of models of autoimmune disease and transplantation. Repeated administration of cationic amphiphiles induces phospholipid accumulation in a variety of species. The present study was conducted to explore the mechanism of phospholipid accumulation in rats caused by treatment with the novel azaspirane, SK&F 106615 (atiprimod). Atiprimod inhibited the activities of partially purified phospholipases A(2) and C, but not D, in a noncompetitive manner in vitro. Treatment of rats for 28 days with 10 mg/kg/day of atiprimod increased the contents of arachidonate-containing molecular species within plasmalogen subclasses of hepatic phosphatidylcholine and phosphatidylethanolamine. In contrast, diacyl-linked species were not affected, indicating a selective effect upon an hepatic plasmalogen-selective phospholipase A(2). Taken together, the data suggest that the beneficial effects of atiprimod in autoimmune diseases may involve inhibition of phospholipase A(2) and C activities. Further, the data suggest that atiprimod is a selective inhibitor of plasmalogen-selective phospholipase A(2) in vivo.

Atiprimod (SK&F 106615), a novel macrophage targeting agent, enhances alveolar macrophage candidacidal activity and is not immunosuppressive in Candida-infected mice.

Azaspiranes are novel macrophage-targeting agents with activity in preclinical animal models of autoimmune disease and transplantation. The purpose of this work was to determine the effects of atiprimod (SK&F 106615), an azaspirane being developed for the treatment of rheumatoid arthritis, on rat pulmonary alveolar macrophage (AM) function and immunocompetance in Candida-infected mice. AM from rats treated with 20 mg/kg/day of atiprimod for 15 days demonstrated enhanced killing of Candida albicans ex vivo. Concentration-dependent increases in candidacidal activity were also observed as early as one hour after exposure in vitro in AM from untreated normal rats. Treatment of AM with atiprimod in vitro did not increase particulate-stimulated superoxide production or phagocytosis of Candida but decreased their ability to concentrate acridine orange, indicating an increase in lysosomal pH. Increased candidacidal activity was inhibited by superoxide dismutase and catalase, suggesting a role for reactive oxygen intermediates (ROI). Atiprimod also increased free radical-mediated killing of Candida in the presence of H2O2, iron and iodide in a cell-free system. These findings indicated that treatment with atiprimod increased the candidacidal activity of rat AM in a free radical-dependent manner. The data also suggested that atiprimod did not increase ROI production by AM, but rather increased the efficiency of radical-mediated killing. This increase may be caused by cyclization of atiprimod, facilitating electron transfer and peroxidation of lipid membranes. In vivo studies in Candida-infected CBA mice showed that atiprimod (10 mg/kg/day), did not compromise immune function in the infected mice and could be differentiated from prototypical immunosuppressive compounds used for treatment of autoimmune diseases.

Evaluation of alamar blue reduction for the in vitro assay of hepatocyte toxicity.

Alamar Blue (AB) reduction is a promising new in vitro assay which is simple to conduct and amenable to repeated measurements and high-throughput screening; however, evaluation with hepatocytes has not been reported. Accordingly, we compared AB reduction with established markers of hepatocyte viability and cell density. Primary rat hepatocytes were allowed to adhere to collagen-coated 96-well plates, then exposed for 16 hours to culture medium, 0.7% dimethyl sulfoxide (DMSO) in medium, 500 mum CCl(4), 500 mum eugenol or 15 or 150 mum of a novel substituted indoline (the latter three in medium with 0.7% DMSO; medium also contained hydrocortisone during exposure period). Using a spectrophotometric plate reader, AB reduction was compared with lactate dehydrogenase release (LDH) release, neutral red (NR) uptake, total protein (TP) and cell seed density. AB reduction showed a linear relationship and good correlation with NR uptake, LDH release, TP and cell density. AB assay precision varied with cell density, but was similar to other assays in cytotoxicity screening. Good correlation with cell density indicates AB to have the potential for assessment of hepatocyte proliferation. From the results reported here, we recommend further evaluation and optimization of a protocol for application of AB reduction as a test for cytotoxicity and proliferation in primary hepatocyte cultures.

Subcutaneous bioavailability of a PRIMATIZED IgG1 anti-human CD4 monoclonal antibody is dose dependent in transgenic mice bearing human CD4.

IDEC-CE9.1/SB-210396 is a macaque/human chimeric IgG1 monoclonal antibody (mAb) directed against the human T-cell surface marker, CD4. This antibody has been evaluated as a potential treatment for rheumatoid arthritis and asthma, in which T cell activation is believed to play an important role in orchestrating inflammation and tissue damage. Human CD4+ murine CD4 knock-out transgenic mice (HuCD4+) have proven most useful in studying the pharmacology of CE9.1, since this antibody cross-reacts only with chimpanzee CD4 and the disposition of the antibody is highly dependent on the presence and distribution of human CD4. In the present study, the distribution and pharmacokinetics of [(3)H]CE9.1 were investigated after subcutaneous (sc) administration to HuCD4+ and murine CD4 knock-out (CD4-) transgenic mice (doses of 0.4 and 100 mg/kg). After a low sc dose to HuCD4+ mice, no absorption of CE9.1 into the systemic circulation was observed. By contrast, high systemic exposure was noted following a comparable sc dose to CD4- mice. Based on evidence that absorption of large proteins occurs primarily via the lymphatics (Supersaxo et al., Pharm. Res. 7:167, 1990), it is proposed that specific binding of CE9.1 to the CD4 molecule on lymphocytes in the regional lymph node(s) prevented the mAb from entering the systemic circulation. Saturation of CD4 binding following a high sc dose to HuCD4+ mice resulted in systemic exposure comparable to that observed at lower doses in CD4- mice. Furthermore, absorption of a low sc dose of [(3)H]CE9.1 was increased 30-fold by administration 7 h earlier of a high sc dose of unlabeled CE 9.1.

Single-organism model of host defense against infection: a novel immunotoxicologic approach to evaluate immunomodulatory drugs.

The immunotoxicologic effects of drugs on host defense have been studied widely using various animal models of infection. Here we describe a new approach to testing host defense by using a single organism (Candida albicans) in CBA/J mice. The model is configured to test 3 effector systems via different routes of inoculation to stimulate different effector arms of the immune response. Nonspecific immunity was evaluated by C. albicans colony-forming unit (CFU) count from the spleen at 2 hr (uptake) and > or = 22 hr (clearance) following intravenous inoculation. Cell-mediated immunity was assessed by CFU count from an intramuscular injection site 6 days postinoculation. Humoral immunity was assessed by anti-Candida antibody titer, following multiple subcutaneous immunizations with C. albicans. Finally, overall immunity was evaluated following intravenous injection using survival as the endpoint. Histopathological, immunohistochemical, and electron microscopic evaluation of selected tissues revealed the involvement of the expected cell types in the different effector systems. Several immunomodulatory drugs--dexamethasone, cyclosporine, liposomal muramyltripeptide phosphatidylethanolamine, and SK&F 105685--were evaluated in the C. albicans model. Dexamethasone impaired host defense against C. albicans by suppressing all endpoints measured. Similarly, cyclosporine showed broad immunosuppressive activity, with the exception of yeast uptake from the spleen. In contrast, muramyl tripeptide-phosphatidylethanolamine enhanced all but cell-mediated immunity to C. albicans. SK&F 105685 displayed both stimulatory and inhibitory effects on immune responses to the infection. Our studies demonstrate that a single organism-based approach can be a useful method for evaluating the immunological hazards of drugs on host resistance to infection.

A novel technique for mapping the lipid composition of atherosclerotic fatty streaks by en face fluorescence microscopy.

We introduce here a new fluorescence microscopy technique for en face analysis of the atherosclerotic fatty streaks (FS). This technique is semiquantitative and has the sensitivity and resolution to map lipids to individual cells in FS less than 100 microns in diameter. New Zealand White rabbits were fed an atherogenic diet for up to 26 weeks. Aortas were fixed in formalin and stained en bloc with the fluorescent dyes Nile red and filipin. Fluorescent staining was validated by correlating microfluorimetric and biochemical measurements of the lipid content in FS. To determine the cell types associated with the different staining patterns, FS were also evaluated by transmission electron microscopy (TEM) and immunohistochemistry (IH). Correlation of microfluorimetry, TEM, IH, and biochemical data indicated that regions rich in non-esterified cholesterol stained with filipin and fluoresced blue owing to accumulations of lipid vesicles and/or cholesterol crystals. Regions rich in neutral and polar lipids stained with Nile red and fluoresced yellow or orange, respectively, owing to accumulations of lipids in both macrophages and smooth muscle cells (SMC). Digital overlays of the filipin and Nile red images revealed that larger lesions (> 0.5 mm diameter) had a "nested" distribution of lipids, with a blue (filipin) fringe surrounding an orange (Nile red) fringe surrounding a yellow (Nile red) center.

Characterization of CD4-gp120 activation intermediates during human immunodeficiency virus type 1 syncytium formation.

The mechanism by which cells expressing HIV envelope glycoproteins progress from binding CD4+ cells to syncytia formation is not entirely understood. The purpose of these investigations was to use physical and biochemical tools (temperature shifts, soluble CD4, protease inhibitors, and a battery of anti-CD4 monoclonal antibodies) to isolate discrete steps during syncytia formation. Previously (Fu et al., J Virol 1993;67:3818), we found that preincubation of cells stably expressing HIV-1 gp 160 (TF228.1.16) with CD4+ SupT1 cells at 16 degrees C, a temperature that is nonpermissive for syncytia formation, resulted in an increased rate of syncytia formation when the cocultures were shifted to the syncytia-permissive temperature of 37 degrees C. We have since found that syncytia formation is further enhanced by shifting the cocultures from 16 to 4 degrees C prior to incubation at 37 degrees C. Together, these data suggest that two discrete states, which we term the first and second activation intermediates (FAI and SAI), are involved in syncytia formation. We have found that acquisition of the FAI (by preincubation at 16 degree C) is sensitive to some serine protease inhibitors (PI), soluble CD4 (sCD4), shedding of gp120, and anti-CD4 monoclonal antibodies (MAb) directed toward the CDR-1/2 and CDR-3 regions of domain 1 on CD4. Expression of the FAI (formation of syncytia by shifting from 16 to 37 degrees C) remains sensitive to sCD4, shedding of gp120, and MAb directed toward CDR-1/2 but is less sensitive to MAb that bind CDR-3 and is insensitive to PI. Similarly, acquisition of the SAI (shifting cocultures from 16 to 4 degrees C), is sensitive to sCD4, shedding of gp120, and MAb directed toward CDR-1/2. In contrast, expression of the SAI (shifting cocultures from 16 to 4 to 37 degrees C) is sensitive only to MAb directed toward CDR-1/2 and cannot be blocked by sCD4, shedding of gp120, or PI. These data allow us to propose that syncytia formation, mediated by HIV-1 envelope glycoproteins, proceeds by a multistep cascade.

Relationships between antibodies against human soluble complement receptor 1 (hsCR1) from various species.

The relationships between antibodies against human soluble complement receptor 1 (hsCR1) were studied in rodents, dogs, nonhuman primates, and humans. An antibody response occurred in all species except humans. The anti-hsCR1 antibodies from the various species were characterized to determine if they recognize similar epitopes on the hsCR1 molecule. Dog and monkey sera, positve for hsCR1 binding, were used as blocking antibodies against mouse anti-hsCR1 monoclonal antibodies as well as mouse and rat anti-hsCR1-positive sera. Human sera (blood group antisera: anti-Knops, anti-McCoy, anti-Knops/McCoy, anti-Swain-Langley) and serum from one burn patient (who became seropositive despite ever receiving treatment with hsCR1) were also used to test blocking of mouse, rat, dog, and monkey anti-hsCR1. Characterization of anti-hsCR1 antibodies from different species demonstrated that hsCR1 causes divergent antibody responses among animals. While mouse, rat, and dog antibodies cross inhibit binding by approximately 50%, monkey antibodies recognize primarily different epitopes of the hsCR1 molecule. Moreover, human antibodies binding hsCR1 are completely different from the animal antibodies, including monkey. This study indicates that although hsCR1 is immunogenic in animals, there is a difference in response between species, particularly between nonprimates and primates, and finally, that this antibody response is not predictive for humans.

Evidence of foam cell and cholesterol crystal formation in macrophages incubated with oxidized LDL by fluorescence and electron microscopy.

Macrophage-derived foam cells are a prominent component of developing atherosclerotic lesions. We describe an in vitro model of foam cell formation which mimics some aspects of the evolution of foam cells in mature atherosclerotic lesions. Thioglycollate-elicited mouse peritoneal macrophages were incubated with copper-oxidized LDL (ox-LDL) for periods up to 168 hr. Identifiable foam cells were present after incubation with ox-LDL at 24, 72, and 168 hr. Control cells incubated without ox-LDL did not form foam cells. Fluorescence microscopy after staining with Nile red exhibited progressive accumulation of lipids, and transmission electron microscopy (TEM) showed distinct ultrastructural changes over time. Macrophages at 24 hr had a few non-membrane-bound lipid droplets but were otherwise identical to control cells. These lipid droplets fluoresced yellow-gold after Nile red staining. After 72 hr of incubation with ox-LDL, in addition to increased numbers of non-membrane-bound lipid inclusions, macrophages contained membrane-bound multilamellar lipoid structures. These multilamellar structures corresponded to areas of reddish-orange fluorescence after Nile red staining. In macrophages incubated with ox-LDL for 168 hr, the amount of cellular lipid was further increased and cholesterol crystal profiles were apparent within some multilamellar lipoid structures. Biochemical analysis showed that the total cholesterol content steadily increased over 168 hr. The increase in total cholesterol was accompanied by a dramatic increase in free cholesterol between 72 and 168 hr. These results demonstrate that long-term incubation of macrophages with ox-LDL increased lipid deposition in cultured cells and that, under the conditions studied, cholesterol crystals formed in macrophage foam cells. Moreover, this system allows investigation of the evolution of foam cells showing some characteristics of those found in atherosclerotic lesions.