Characterization of two monoclonal antibodies obtained after immunization with human liver mitochondrial membrane preparations

The calcium-sensitive large-conductance potassium channel (BK/MAXI K) is present in the inner mitochondrial membrane of rat brain

Large-conductance voltage- and calcium-sensitive channels are known to be expressed in the plasmalemma of central neurons; however, recent data suggest that large-conductance voltage- and calcium-sensitive channels may also be present in mitochondrial membranes. To determine the subcellular localization and distribution of large-conductance voltage- and calcium-sensitive channels, rat brain fractions obtained by Ficoll-sucrose density gradient centrifugation were examined by Western blotting, immunocytochemistry and immuno-gold electron microscopy. Immunoblotting studies demonstrated the presence of a consistent signal for the alpha subunit of the large-conductance voltage- and calcium-sensitive channel in the mitochondrial fraction. Double-labeling immunofluorescence also demonstrated that large-conductance voltage- and calcium-sensitive channels are present in mitochondria and co-localize with mitochondrial-specific proteins such as the translocase of the inner membrane 23, adenine nucleotide translocator, cytochrome c oxidase or complex IV-subunit 1 and the inner mitochondrial membrane protein but do not co-localize with calnexin, an endoplasmic reticulum marker. Western blotting of discrete subcellular fractions demonstrated that cytochrome c oxidase or complex IV-subunit 1 was only expressed in the mitochondrial fraction whereas actin, acetylcholinesterase, cadherins, calnexin, 58 kDa Golgi protein, lactate dehydrogenase and microtubule-associated protein 1 were not, demonstrating the purity of the mitochondrial fraction. Electron microscopic examination of the mitochondrial pellet demonstrated gold particle labeling within mitochondria, indicative of the presence of large-conductance voltage- and calcium-sensitive channels in the inner mitochondrial membrane. These studies provide concrete morphological evidence for the existence of large-conductance voltage- and calcium-sensitive channels in mitochondria: our findings corroborate the recent electrophysiological evidence of mitochondrial large-conductance voltage- and calcium-sensitive channels in glioma and cardiac cells.

Nuclear localization of L-type glutaminase in mammalian brain

In mammals, there are two different genes encoding for glutaminase isoforms, named liver (LGA) and kidney (KGA) types. LGA has long been believed to be present only in liver mitochondria from adult animals. However, we have recently reported the presence of LGA mRNA in human brain. We now describe the expression of LGA mRNA in the brain of other mammals (cow, mouse, rabbit, and rat) and in different areas of human brain as assessed by Northern blot analysis. The presence of mRNA encoding for this isoform in rat brain was further confirmed by reverse transcriptase-PCR cloning and sequencing. Although it has been well accepted that glutaminase is a mitochondrial enzyme, using newly generated isoform-specific antibodies, we have found a differential intracellular immunolocalization of both glutaminase isoforms in rat and monkey brain. In both species, KGA protein was present in mitochondria, whereas LGA protein was localized in nuclei. Furthermore, subcellular fractionation and Western blot analysis revealed that brain LGA was enriched in nuclei where it was catalytically active. Nuclear glutaminase exhibited a kinetic behavior that resembles that of the liver-type enzyme with regard to the low phosphate concentration requirement; however, nuclear glutaminase was susceptible to glutamate inhibition, a property that is absent in the rat liver enzyme.

Putative liver progenitor cells: conditions for long-term survival in culture

Oval cells proliferate extensively in the livers of animals exposed to oncogenic insults, are bipotent and are believed to be related to the so far unidentified liver stem cell. In normal liver, cells antigenically related to oval cells and expressing liver and epithelial markers are considered to be liver progenitor cells. We isolated, by fluorescence-activated cell sorting or magnetic bead sorting, cells expressing the oval cell antigens OC.2 or OC.3 from the liver of normal newborn or day 12 embryonal age rats. Magnetic bead sorting of positive cells was as efficient as fluorescence-activated cell sorting. A two-chamber culture system was devised in which cells were plated onto transwell filters coated with type IV collagen and cultured in a serum-free Ham's F12 medium supplemented with free fatty acids and bovine serum albumin. Under these conditions, cells remained viable for up to 6 weeks and their antigenic phenotype was unchanged throughout. Approximately 30% of sorted cells expressed epithelial and/or liver-specific markers. Growth factors mitogenic for epithelial cells and hepatocytes did not elicit cell proliferation. These results provide an important background for further studies designed to determine the biological significance of OC.2+ and OC.3+ cells in normal liver, to test the liver stem cell hypothesis and to develop protocols for the expansion in vitro of normal liver progenitors.

A flow-cytometric method to evaluate drug antiaggregating effect on rat neutrophils

Neutrophils are one of the first cellular populations to become involved in inflammatory processes and some features of the response to inflammatory stimuli can be partially reproduced in vitro by treatment with chemotactic peptides such as N-formyl-methionyl-leucyl-phenylalanine (FMLP). Nonsteroidal antiinflammatory drugs (NSAIDs), such as indomethacin, are known to interfere in vitro with human and rat neutrophil functions and to inhibit FMLP-induced aggregation. In this article we define the scatter parameters of rat neutrophils and demonstrate that flow-cytometric analysis of these cells can be used to analyze the inhibiting action of drugs in an in vitro model of aggregation. We show, in fact, that indomethacin at 100 microM (p < 0.05) and 200 microM (p < 0.01) is able to significantly reduce rat neutrophil aggregation. These results confirm the data obtained by light transmittance aggregometry and indicate that cytometric analysis of aggregation phenomena is a technique suitable for the screening of antiaggregating drugs.

Metabolic modulation of hexokinase association with mitochondria in living smooth muscle cells

Hexokinase isoform I binds to mitochondria of many cell types. It has been hypothesized that this association is regulated by changes in the concentrations of specific cellular metabolites. To study the distribution of hexokinase in living cells, fluorophore-labeled functional hexokinase I was prepared. After microinjection into A7r5 smooth muscle cells, hexokinase localized to distinct structures identified as mitochondria. The endogenous hexokinase demonstrated a similar distribution with the use of immunocytochemistry. 2-Deoxyglucose elicited an increase in glucose 6-phosphate (G-6-P) and a decrease in ATP levels and diminished hexokinase binding to mitochondria in single cells. 3-O-methylglucose elicited slowly developing decreases in all three parameters. In contrast, cyanide elicited a rapid decrease in both ATP and hexokinase binding. Analyses of changes in metabolite levels and hexokinase binding indicate a positive correlation between binding and cell energy state as monitored by ATP. On the other hand, only in the presence of 2-deoxyglucose was the predicted inverse correlation between binding and G-6-P observed. Unlike the relatively large changes in distribution observed with the fluorescent-injected hexokinase, cyanide caused only a small decrease in the localization of endogenous hexokinase with mitochondria. These findings suggest that changes in the concentrations of specific metabolites can alter the binding of hexokinase I to specific sites on mitochondria. Moreover, the apparent difference in sensitivity of injected and endogenous hexokinase to changes in metabolites may reflect the presence of at least two classes of binding mechanisms for hexokinase, with differential sensitivity to metabolites.

Phenotypic analysis of pulmonary perivascular mononuclear infiltrates that occur as a direct result of acute lethal graft-versus-host disease describes the onset of interstitial pneumonitis

We recently determined that the sequential development of interstitial pneumonitis and lymphocytic bronchiolitis/bronchitis occurs as a direct result of acute lethal graft-versus-host disease. Interstitial pneumonitis develops before lymphocytic bronchiolitis/bronchitis primarily from the dissemination of perivascular mononuclear infiltrates. We have used the adult, nonirradiated (DA x LEW) F1 hybrid rat in the absence of chemotherapy, immunosuppression, or overt infection to determine the phenotype of infiltrating perivascular mononuclear cells throughout acute lethal graft-versus-host disease. F1 animals were intravenously injected with 1 x 10(6) DA parental lymphoid cells/g body weight, which produced 100% morbidity and mortality by day 21. Graft-versus-host disease animals were killed on days 3, 7, 10, 14, and 15 to 21 after injection. Whole left lung lobes were frozen, serially sectioned (4 microns), and incubated with a panel of mouse anti-rat monoclonal antibodies. Labeled antibody density was determined by computerized image analysis. Perivascular infiltration was observed first for ED1+, OX8+, and W3/25+ cells, and then OX41+, W3/13+ and OX19/25+ populations. OX6 was expressed in control tissues and at all time points tested. OX12+, OX39+ and MOM/3F12/F2+ cells were not quantifiable. The present study has determined that the process of perivascular infiltration was produced through a biphasic influx of OX6+, T-cell, and macrophage populations.

Subcellular localization of pyruvate dehydrogenase dihydrolipoamide acetyltransferase in human intrahepatic biliary epithelial cells

In previous histological studies, biliary epithelial cells (BEC) in the liver of patients with primary biliary cirrhosis (PBC), but not controls, reacted strongly with antibodies specific for the major autoantigen associated with PBC, the E2 component of pyruvate dehydrogenase complex (PDC-E2). In this study we have used transmission electron microscopy (TEM) to document the precise subcellular localization of PDC-E2 in BEC. Two antibodies which recognize PDC-E2 were used: affinity-purified anti-PDC-E2 raised in rabbits; and human antibody from the serum of patients with PBC, affinity-purified against human heart PDC. The intracellular localization of antibody binding was determined by laser scanning confocal microscopy and TEM. Both antibodies bound to the inner membrane of mitochondria in BEC isolated from both patients with PBC and controls, but binding to the external aspect of the plasma membrane was observed only in BEC from patients with PBC. Surface antigen expression in PBC may make BEC immunological targets.

Interleukin-1β inhibits luteinizing hormone-induced plasminogen activator activity in rat preovulatory folliclesin vitro

The effects of interleukin-1β (IL-1β) and tumour necrosis factor-α (TNFα) on ovulation-associated plasminogen activator (PA) activity were investigated using preovulatory follicles excised 48h after equine chorionic gonadotrophin (16IU)-priming of immature rats. Follicles were incubated for 6 and 14h with a single dose of LH (1 μg/ml) only, or various cytokine doses in the presence or absence of LH. PA activity in follicular homogenates was determined by a radioactively labelled fibrin-coated plate method and secreted levels of the ovulatory mediators progesterone (P) and prostaglandin E (PGE) were measured by radioimmunoassay. LH induced timedependent rises in PA (2.5-fold over control at 6h and fourfold over control at 14h), while IL-1β and TNFα alone had no effect over either time period. LH and cytokine coincubations over 14h revealed that IL-1β dosedependently inhibited the LH-induced increase in PA activity, up to 85%. The effects of TNFα on LH-induced PA activity were not significant. Both IL-1β and TNFα increased P and PGE secretion time- and dose-dependently. In summary, IL-1β dose-dependently inhibits the LH-induced increase in PA activity in rat preovulatory folliclesin vitro while, as with TNFα, increasing P and PGE synthesis. This study, shows that the earlier reported pro-ovulatory action of IL-1β is not likely to be mediated by activation of the PA-system and suggests that IL-1β may mediate a regulatory loop controlling the extent and distribution of LH-induced PA activity in rat preovulatory follicles.

Distribution of pyruvate dehydrogenase dihydrolipoamide acetyltransferase (PDC-E2) and another mitochondrial marker in salivary gland and biliary epithelium from patients with primary biliary cirrhosis

Previous studies in which quantitative immunofluorescence was used have shown that certain biliary epithelial cells in liver with primary biliary cirrhosis show increased levels of pyruvate dehydrogenase dihydrolipoamide acetyltransferase compared with controls. This study was designed to determine whether the increase in intensity of pyruvate dehydrogenase dihydrolipoamide acetyltransferase in biliary epithelial cells is accounted for by an increase in the number of mitochondria in the same cells. A double-antibody staining technique was used with antibodies specific for pyruvate dehydrogenase dihydrolipoamide acetyltransferase and another mitochondrial inner membrane marker, recognized by the mouse monoclonal antibody MCA151A. Distribution of the antigens was studied in sections of liver and salivary gland, an additional site that is frequently involved in primary biliary cirrhosis. Confocal microscopy was used to quantify the intensity of fluorescence resulting from binding of fluorochrome-labeled antibody. In both liver and salivary glands MCA151A binding was similar in normal and sections with primary biliary cirrhosis and corresponded to the predicted distribution of mitochondria in these tissues. In the liver staining was less intense in biliary epithelial cells than in hepatocytes. In salivary gland binding of both antibodies was predominantly localized to duct cells, with those forming striated ducts, known to be rich in mitochondria, being most intensely stained. There was high coincidence of the two antigens in salivary glands (p < 0.01) and in biliary epithelial cells from normal liver (p = 0.01). However, in liver with primary biliary cirrhosis, despite high coincidence between the antigens on hepatocytes, biliary epithelial cells showed high intensity of pyruvate dehydrogenase dihydrolipoamide acetyltransferase but not MCA151A.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential activation of microglia and astrocytes in aniso- and isomorphic gliotic tissue

Reactive astrocytes and microglial cells are both involved in the formation of gliotic tissue. Using immunohistochemical markers, we have compared the response of both these cell types after two different kinds of damage in the brain: traumatic injury (anisomorphic gliosis) and neurotoxic induced lesion (isomorphic gliosis), in two distinct regions of the brain, the cortex and the hippocampus. We show that the time course and the relative contribution of astrocytes and microglial cells differ greatly in the two kinds of lesions. While in anisomorphic gliosis there is little activation of endogenous microglial cells independently of the brain region damaged, these cells contribute in large measure and for prolonged periods of time to the formation of isomorphic gliotic tissue. Astrocytes are quickly activated at the border of anisomorphic lesions, and after 3 days they already occupy an extensive portion of the brain parenchyma. However, after 1 month, they are found restricted to a thin strip at the lesion boundary. In contrast, after an isomorphic lesion, astrocytes become reactive around the site of neuronal cell loss but not at the site of the lesion itself. Only after 2 weeks do they totally invade the damaged region, persisting for at least 1 month. Such differences are observed independently of the brain region damaged. These results suggest that the cellular, and therefore the molecular, composition of gliotic tissue depends on the type of insult the CNS has suffered.

Polymorphonuclear leukocytes in brain parenchyma after injury and their interaction with purified astrocytes in culture

At a time after brain injury when removal of debris and secondary cell death were prevalent, many polymorphonuclear neutrophils were observed in injured tissue. Because neural damage could be mediated by activated neutrophils, we tested in vitro the effect of these leukocytes and other blood components on central nervous system cells. At concentrations similar to those present in blood, polymorphonuclear leukocytes resulted in astrocyte detachment from the substrate and aggregation. These neutrophil concentrations affected both epithelioid and stellate HNK1/A2B5-negative (type 1) astrocytes but not hippocampal neurons. Substrate detachment was partially prevented by corticosterone, but not by protease inhibitors or free-radical scavengers. Co-cultures of purified cortical astrocytes with neutrophils (1/20 cell ratio) contained at the beginning of the experiment approximately 93-98% astrocytes with type 1 markers. After 6-8 days co-culture, many stellate cells insensitive to neutrophils seemed to migrate out of the aggregates. About 70% of these resistant cells had immunological markers typical of type 2 astrocytes. The possible relevance of these findings to reactive astrogliosis and secondary neuronal death is discussed.

An enzyme immunoassay for the measurement of human monoamine oxidase B protein

A heterologous, competitive, solid phase ELISA has been developed which can measure monoamine oxidase (MAO) B concentration (both inactive and active) in human platelets and other tissue extracts. The assay is based on competition between a soluble form of MAO and MAO bound to a solid phase for binding to a limiting amount of a MAO B-specific monoclonal antibody, 3F12/G10. It utilises a crude and easily prepared sample of human liver mitochondrial membranes as the source of solid phase MAO. Optimal assay conditions allow detection of MAO B down to at least 0.5 ng (4.18 fmol; 6.25 ng/ml) of protein. As the assay is sensitive and simple to operate, it will allow a systematic assessment of the role of platelet MAO concentrations in the aetiology of psychiatric and neurologic conditions.

Modulation of hexokinase association with mitochondria analyzed with quantitative three-dimensional confocal microscopy

Hexokinase isozyme I is proposed to be associated with mitochondria in vivo. Moreover, it has been suggested that this association is modulated in coordination with changes in cell metabolic state. To test these hypotheses, we analyzed the subcellular distribution of hexokinase relative to mitochondria in paraformaldehyde-fixed astrocytes using immunocytochemistry and quantitative three-dimensional confocal microscopy. Analysis of the extent of colocalization between hexokinase and mitochondria revealed that approximately 70% of cellular hexokinase is associated with mitochondria under basal metabolic conditions. In contrast to the immunocytochemical studies, between 15 to 40% of cellular hexokinase was found to be associated with mitochondria after fractionation of astrocyte cultures depending on the exact fractionation conditions. The discrepancy between fractionation studies and those based on imaging of distributions in fixed cells indicates the usefulness of using techniques that can evaluate the distributions of "cytosolic" enzymes in cells whose subcellular ultrastructure is not severely disrupted. To determine if hexokinase distribution is modulated in concert with changes in cell metabolism, the localization of hexokinase with mitochondria was evaluated after inhibition of glucose metabolism with 2-deoxyglucose. After incubation with 2-deoxyglucose there was an approximate 35% decrease in the amount of hexokinase associated with mitochondria. These findings support the hypothesis that hexokinase is bound to mitochondria in rat brain astrocytes in vivo, and that this association is sensitive to cell metabolic state.

Auto-MHC class II-reactive T cell line obtained from MRL/+mice suffering from "lpr-GVHD". I. Characterization of surface phenotypes, specificities and functions in vitro

When MRL/Mp-(+)/+ (MRL/+) mice are lethally irradiated and then reconstituted with bone marrow or spleen cells from MRL/Mp-lpr/lpr (MRL/lpr) mice, they develop a graft-versus-host disease (GVHD)-like syndrome, colloquially known as "lpr-GVHD". To analyze the roles of the MRL/lpr T cells in the development of "lpr-GVHD" and autoimmune diseases, several T cell lines were established from the spleen cells of MRL/+ mice suffering from "lpr-GVHD". The surface phenotypes, specificities, and functions of a representative clone (l/+T1) of the cloned T cell lines were characterized. The l/+T1 cells showed Thy-1.2+, L3T4+ and T3+, but Lyt-2- and B220- phenotypes. Proliferative response was observed by co-culturing the cells with spleen cells from MRL/+, MRL/lpr, AKR/J, and C3H/HeN mice, but not from BALB/c or C57BL/6 mice. Furthermore, the l/+ T1 cells responded to spleen cells of B10.BR and B10.A but not B10.D2 mice. The proliferative response of l/+ T1 cells to MRL/+ spleen cells was inhibited by anti-I-Ek (but not anti-I-Ak or anti-Kk) antibodies, suggesting that the specificity of l/+T1 cell culture enhanced the proliferative response only in the presence of appropriate stimulators. Treatment of stimulator cells with J11d.2 + C (but not anti-Thy-1.2 + C or 33D1 + C) abolished the stimulatory effect, indicating that B cells are effective stimulator cells for auto-MHC class II-reactive l/+T1 cells. When MRL/+ splenic B cells were co-cultured with l/+T1 cells, both B cell proliferation and IgM production were observed. In addition, IgM-class rheumatoid factor and anti-ssDNA antibody activities were found in the supernatants of MRL/+ splenic B cells co-cultured with l/+T1 cells. These results are discussed in relation to "lpr-GVHD" and autoimmunity in MRL/lpr mice.

A monoclonal antibody recognizing selectively rat granulocytes

In the present study, a murine monoclonal antibody, RK-4 (IgG1) specific for rat granulocytes and their precursors in blood and bone marrow is described. Results obtained by immunocytological and flowcytometry analysis showed this mAb to recognize selectively a surface antigen on neutrophils, eosinophils and basophils. Analysis of cryosections of various lymphatic and non-lymphatic organs demonstrates that this mouse antibody does not cross-react with any other structures. By flow cytometric analysis we found peripheral blood leukocytes to consist of about 15-20% granulocytes. RK-4 is therefore a valuable tool for studying differentiation and function of granulocytes under various conditions.

Biochemical and histologic findings in experimental pyelonephritis due to Ureaplasma urealyticum

Ureaplasma urealyticum has previously been shown to be capable of persisting in the rat kidney for up to 6 months following a single reflux challenge. We examined kidney tissue from infected animals for evidence of renal damage by using standard cytochemical and immunoenzyme methods. We also monitored changes in renal function during a 6-month study period with standard biochemical assays of plasma and urine. Histologic examination showed tubular atrophy, interstitial fibrosis, and a mononuclear infiltrate in proportion to ureaplasma counts from renal tissue. The most severe damage was accompanied by hyaline cast formation within tubules which gave rise to the typical thyroidlike appearance of chronic pyelonephritis involving conventional urinary pathogens. Macroscopic renal scarring occurred in some animals. Although damage to the renal medulla was moderate to severe, only minor changes were seen in the cortex, and glomeruli were invariably spared. Biochemical tests of renal function showed similar changes in infected and uninfected animals during the study period. Interstitial inflammation was characterized by a mononuclear cell infiltrate in which polymorphonuclear leukocytes were not conspicuous. It is evident that U. urealyticum is capable of producing chronic pyelonephritis in the rat after a single reflux challenge. The results of this study have obvious implications for the pathogenicity of these bacteria in human pyelonephritis.

Surface phenotype of rat bone marrow-derived mononuclear phagocytes

Utilizing a panel of currently available monoclonal antibodies, the surface phenotype of a pure population of resting rat bone marrow-derived mononuclear phagocytes (BMM phi) was analyzed by means of flow cytometry. The present work provides an extensive list of surface markers expressed by BMM phi and also outlines advantages and limitations of flow cytometric analysis of this cell type. The results show that the majority of surface markers considered to be expressed selectively by T lymphocytes, such as Thy-1, CD2 and CD5 antigens, leukosialin (W3/13), or an alloantigen of peripheral T cells, are not expressed by BMM phi. On the other hand, the CD8 antigen and the leukocyte common antigen recognized by MRC OX-33, considered to represent specific markers of cytotoxic T cells and/or peripheral B cells, are expressed on a variable, often considerable proportion of BMM phi. Monoclonal antibodies W3/25, MRC OX-35, and MRC OX-38, directed against epitopes on the CD4 molecule, labeled a variable proportion of BMM phi. Among the 39 monoclonal antibodies examined, none appeared to recognize an epitope which is expressed selectively by mononuclear phagocytes.

Differential regulation of mRNA encoding nerve growth factor and its receptor in rat sciatic nerve during development, degeneration, and regeneration: role of macrophages

In newborn rats the levels of nerve growth factor (NGF) mRNA (mRNANGF) and NGF receptor mRNA (mRNA(rec)) in the sciatic nerve were 10 and 120 times higher, respectively, than in adult animals. mRNA(rec) levels decreased steadily from birth, approaching adult levels by the third postnatal week, whereas mRNANGF levels decreased only after the first postnatal week, although also reaching adult levels by the third week. Transection of the adult sciatic nerve resulted in a marked biphasic increase in mRNANGF with time. On the proximal side of the cut, this increase was confined to the area immediately adjacent to the cut; peripherally, a similar biphasic increase was present in all segments. mRNA(rec) levels were also markedly elevated distal to the transection site, in agreement with previous results obtained by immunological methods [Taniuchi, M., Clark, H. B. & Johnson, E. M., Jr. (1986) Proc. Natl. Acad. Sci. USA 83, 4094-4098]. Following a crush lesion (allowing regeneration), the mRNA(rec) levels were rapidly down-regulated as the regenerating nerve fibers passed through the distal segments. Down-regulation of mRNANGF also occurred during regeneration but was slower and not as extensive as that of mRNA(rec) over the time period studied. Changes in mRNANGF and mRNA(rec) occurring in vivo after transection were compared with those observed in pieces of sciatic nerve kept in culture. No difference was found for mRNA(rec). Only the initial rapid increase in mRNANGF occurred in culture, but the in vivo situation could be mimicked by the addition of activated macrophages. This reflects the situation in vivo where, after nerve lesion, macrophages infiltrate the area of the Wallerian degeneration. These results suggest that mRNANGF synthesis in sciatic non-neuronal cells is regulated by macrophages, whereas mRNA(rec) synthesis is determined by axonal contact.

A monoclonal antibody specific for the red-absorbing form of phytochrome

Characterisation of a new monoclonal antibody (mAb), designated LAS 41, directed against 124-kilodalton (kDa) etiolated-oat (Avena sativa L.) phytochrome, indicates that it recognises an epitope unique to the red-light-absorbing form, Pr. In a solid-phase enzyme-linked immunosorbent assay (ELISA), LAS 41 exhibits a seven- to eight-fold higher affinity for Pr than for the far-red-light-absorbing form of phytochrome, Pfr. In addition, in immunoprecipitation assays LAS 41 effectively precipitates 100% of phytochrome presented as Pr but only precipitates a maximum of 24.5% of phytochrome presented as Pfr. These values are indicative of binding exclusively to Pr. Peptide-mapping studies show that LAS 41 recognises and epitope located within a region 6-10 kDa from the aminoterminus of the phytochrome molecule. Since binding of LAS 41 to Pr induces alterations in the spectral properties of Pr, this indicates that at least part of the 4 kDa domain to which the antibody binds is essential for protein-chromophore interaction. Subsequent photoconversion of LAS 41-Pr complexes produces native Pfr spectra, with concomitant production of free antibody and antigen, as shown by a modified ELISA. The specificity of LAS 41 for Pr has facilitated the purification of Pfr which is free of contaminating Pr. This has enabled direct determination of the mole fraction of Pfr established by red light to be 0.874.

Cellular events during hepatocarcinogenesis in rats and the question of premalignancy

The cellular, biochemical, and genetic changes that occur in the liver of rats exposed to chemical hepatocarcinogens are reviewed. Multiple new cell types appear in the liver of carcinogen-treated rats including foci, nodules, ducts, oval cells, and atypical hyperplastic areas. The application of phenotypic markers for these cell types suggests that hepatocellular carcinomas may arise from more than one cell type, including a putative liver stem cell that proliferates following carcinogen exposure. Study of DNA, RNA, and proteins produced by hepatocellular carcinomas and putative premalignant cells has so far failed to identify a gene or gene product clearly associated with the malignant or premalignant phenotype. Understanding the cellular lineage from normal cell through putative premalignant cell to cancer is critical to understanding the process of carcinogenesis. Application of new immunological (monoclonal antibody, transplantation) and molecular biological (gene cloning, oncogene identification) approaches to this problem holds promise that the process of hepatocarcinogenesis will be better known in the near future.

Monoclonal antibodies raised against a subsequence of senile plaque core protein react with plaque cores, plaque periphery and cerebrovascular amyloid in Alzheimer's disease

Four monoclonal antibodies (1D2/1/2, 1G10/2/3, 3B6/1/1, 4D12/2/6) were raised against a synthetic peptide consisting of residues 8-17 of a protein reported to be common to senile plaque cores, cerebrovascular amyloid and neurofibrillary tangles in Alzheimer's disease. In an immunoperoxidase study of Alzheimer brain tissue, these antibodies stained plaque and vascular amyloid but not tangles, suggesting that the polypeptide chain in the region of residues 8-17 is exposed in the former two but, if present, inaccessible in the latter. In addition, staining of granular material in the plaque periphery was observed. These antibodies will be useful tools for future work on the origin of this protein.

Monoclonal antibodies to monoamine oxidase B and another mitochondrial protein from human liver

A monoclonal antibody has been generated to human liver monoamine oxidase (MAO) B by fusion of mouse myeloma cells with spleen cells from a mouse immunized with a mixture of semi-purified MAO A and MAO B. The antibody, 3F12/G10, an immunoglobulin G1, reacts with its antigen in cryostat sections of human liver, showing an intracellular particulate distribution as demonstrated by immunoperoxidase staining. The antibody indirectly precipitates [3H]pargyline-labelled human MAO B both from liver and platelet extracts but fails to precipitate MAO A from liver extracts. The antibody does not recognise rat liver MAO B, showing that the determinant is not universally expressed on MAO B. The antibody has no effect on the catalytic activity of MAO B. Other monoclonal antibodies were generated but they are directed to a protein with a subunit Mr of 54 000, a contaminant of the MAO preparation. One of these antibodies, A8/C2, an IgG2a, reacts with the same protein in both rat and human liver extracts.