[Promotive effect of TNF-alpha and M-CSF on osteolysis induced by giant cell tumor of bone]

OBJECTIVE

To explore the effect of cell components in giant cell tumor of bone (GCT) and cytokines expressed by them on osteolysis.

METHODS

Mononuclear stromal cells and multinucleated giant cells (MGCs) were isolated from 10 cases of GCT, and fibroblast-like stromal cells were obtained by long-term culture of mononuclear stromal cells. Osteolytic capability of above isolated cells were tested in an in vitro cell-bone resorption model.

RESULTS

All cell components isolated from GCT had capability to resorb bone matrix directly. Exogenous tumore necrosis factor-alpha (TNF-alpha) could significantly increase the bone resorption induced by both kinds of stromal cell. There were higher level of TNF-alpha and greater expression rate of macrophage colony stimulating factor (M-CSF) in GCT than in the osteosarcoma tissues or the normal serum.

CONCLUSIONS

The characteristic bone resorption behavior of GCT might be conducted by all it's three major cell components, and this bone resorption process could be promoted by both TNF-alpha and M-CSF they expressed.

Genomic characterization of members of the Bet v 1 family: genes coding for allergens and pathogenesis-related proteins share intron positions

Bet v 1, the major birch pollen allergen, is a member of a multigene family; a number of isoforms and homologous proteins from closely related species (alder, hazel and hornbeam) has been isolated and their cDNAs cloned and characterized. Genomic clones coding for Bet v 1 and homologues from apple and hazel were isolated and sequenced. Some of these clones contained intervening sequences. The exon-intron formation is highly conserved throughout this family of pathogenesis-related proteins in dicot plants and is also found in Aopr1 (Asparagus officinalis), a monocol species. Phylogenetic analysis suggested a possible common origin of the intron position in these homologous proteins at codon 62 in various families of flowering plants, including Fagaceae, Rosaceae and Apiaceae. This conserved 'proto-splice site' may point to a structure/function relationship. A conserved sequence motif (P-loop) was also found in all members of this protein family. Moreover, there is a certain degree of sequence similarity among the proteins derived from various species throughout the dicots and the only monocot examined. This fact is reflected by cross-reactivity from monoclonal and polyclonal antibodies raised against Bet v 1.

[Thermoregulation under simulated weightlessness]

The effect of simulated weightlessness on thermoregulation was studied in 5 subjects. The experiment consisted of 3d baseline measurements, 7d head-down bed rest and 2d recovery. Circadian rhythm was assessed by continuous measurements of rectal temperature and skin temperature with 2h intervals. Heat Stress Protein 70 (HSP70) was measured by Western-blot Dot method and the facial surface temperature distribution was measured by HR-2 infrared thermography. The results showed that rectal temperature keeps the wake-sleep variation, but the circadian rhythm changed during bed rest, and the change of rectum temperature rhythm appeared mainly in the early-days of bed rest; HSP70 and facial surface temperature increased during bed rest.

Inhibition of expression of PKC-alpha by antisense mRNA is associated with diminished cell growth and inhibition of amylase secretion by AR4-2J cells

AR4-2J pancreatoma cells were stably transfected with an expression vector containing the cDNA for PKC-alpha in the antisense orientation. Transfectants designated antisense-alpha AA1, AA2, and AA3 exhibited marked reductions in PKC-alpha expression and decrements in cell growth. The magnitude of the decrement in cell growth paralleled the reduction in PKC-alpha expression, i.e., AA3 > AA1 > AA2. The ability of dexamethasone to induce cell differentiation as assessed by a rise in cellular amylase levels was not markedly affected by the reduction in PKC-alpha expression. Unstimulated amylase release was attenuated in AA1 cells and almost completely blocked in AA2 transfectants. The AA2 transfectant cell line failed to elicit a secretory response to caerulein, and the AA1 transfectant exhibited a lack of the secondary phase of stimulated amylase secretion. These findings demonstrate that PKC-alpha is involved in the mechanisms regulating growth and secretion in AR4-2J cells, but is not necessary for the induction of amylase stores following differentiation.

Carbon dioxide in the atmosphere: isotopic exchange with ozone and its use as a tracer in the middle atmosphere

Atmospheric heavy ozone is enriched in the isotopes 18O and 17O. The magnitude of this enhancement, of the order of 100%, is very large compared with that commonly known in atmospheric chemistry and geochemistry. The heavy oxygen atom in heavy ozone is therefore useful as a tracer of chemical species and pathways that involve ozone or its derived products. As a test of the isotopic exchange reactions, we successfully carry out a series of numerical experiments to simulate the results of the laboratory experiments performed by Wen and Thiemens [1993] on ozone and CO2. A small discrepancy between the experimental and the model values for 17O exchange is also revealed. The results are used to compute the magnitude of isotopic exchange between ozone and carbon dioxide via the excited atom O(1D) in the middle atmosphere. The model for 18O is in good agreement with the observed values.

[The effects of endothelin and bFGF on proliferation of MC and synergetic effect of insulin]

The effects of basic fibroblast growth factor (bFGF), insulin and endothelin-1 (ET-1) on proliferation of rat glomerular mesangial cells (MC) cultured in vitro and the synergetic effects of insulin and bFGF or ET-1 on MC proliferation were determined by H-TdR incorporation experiment. The results showed that bFGF at concentrations of 5-200 ng/ml and insulin at concentrations of 0.1-2.4 U/ml significantly increased the value of 3H-TdR incorporated into MC (the cpm value). The effect of ET-1 on the cpm value was different at different doses. At concentration ranging from 10(-9) mol/L to 10(-7) mol/L, the cpm value significantly increased with increasing the concentration of ET-1, and the highest value was at concentration of 10(-8) mol/L, However, the cpm value decreased at concentration of 10(-6) mol/L ET-1. When MCs were incubated simultaneously with insulin and bFGF or lower concentration of ET-1 (< 10(-8) mol/L), the cpm value was significantly higher than the sum of that induced independently by insulin and bFGF or ET-1. But the joint effect of insulin and higher concentration of ET-1 (> 10(-7) mol/L) on the cpm value was lower than the sum of that induced separately by insulin and ET-1. It was indicated that bFGF, insulin and ET-1 significantly stimulated MC proliferation; insulin exhibited positive synergetic effect with bFGF or lower concentration of ET-1 on MC proliferation, negative synergetic effect with higher concentration of ET-1 on MC proliferation.

[Studies on the chemical constituents of Litsea glutinosea]

Two crystalline substances are isolated from aerial parts of Litsea glutinosea (Lour.) C. B. Rob. and are identified as a-phenylcinnamic acid and p-cumarric acid.

Absorption of calcium, zinc, and iron from breast milk by five- to seven-month-old infants

Data are scarce regarding mineral bioavailability from human milk in older infants who may also be receiving solid foods (beikost). We measured the absorption of Ca, Zn, and Fe in 14 healthy, nonanemic 5-7-mo-old breast-fed infants whose mothers milk was extrinsically labeled with stable isotopes (44Ca, 70Zn, and 58Fe) of these minerals. In addition, Ca and Zn stable isotopes (46Ca and 67Zn) were administered i.v., and a second isotope of Fe (57Fe) was given orally without food as a non-meal dose. Subjects were not receiving any artificial infant formula or cow's milk, but most (10/14) were receiving beikost. Ca and Zn absorption was calculated using the urinary excretion of the isotopes during the 24 h after dosing (Ca) or their urinary ratio 72 h after dosing (Zn). Fe absorption was calculated using the red blood cell incorporation at 14 d. Fe absorption averaged 20.7 +/- 14.8% from the 58Fe given with human milk (geometric mean, 14.8%) and 17.7 +/- 15.1% (geometric mean, 11.0%) from the 57Fe non-meal dose. Ca absorption averaged 61.3 +/- 22.7% and Zn absorption (n = 10) averaged 49.5 +/- 18.5%. Absorption of Fe (natural logarithm) from the non-meal Fe dose (57Fe) but not from the human milk (58Fe) was significantly negatively correlated to serum ferritin (r = -0.70, p = 0.007 versus r = -0.35, p = 0.24). At the intake levels in this study, total daily Fe, Ca, and Zn intakes from beikost were not significantly correlated to their fractional absorption from breast milk, but Fe intake from beikost was significantly negatively correlated to absorption of Fe from the non-meal dose (r = -0.61, p = 0.021). We conclude that minerals are well absorbed from human milk in older infants after the introduction of beikost to the diet.

A receptor binding site on intrinsic factor is located between amino acids 25-44 and interacts with other parts of the protein

A receptor-binding region of intrinsic factor (IF) has been localized to amino acid residues 25-44 by in vitro transcription/translation studies. To further define sites within the region that are necessary for binding, the effects on binding activity of brush border membranes were tested when peptides corresponding with residues 1-44 were added to normal IF and when point mutations were made between residues 25 and 44. Both human IF and IF-cobalamin (cbl) complex bound equally to membranes. None of the peptides tested inhibited human IF or IF-cbl complex binding. Both control rat IF and rat IF that was mutated to be like human IF in residues 25-44 bound to guinea pig and rat membranes; the mutant with altered charge showed 50- to 100-fold decreased affinity. Thus, the putative receptor binding region is important, but cannot alone account for all the physiologic parameters of IF binding. Conformational changes in IF are additionally important.

Structural characterization of an alpha-amylase inhibitor from a wild common bean (Phaseolus vulgaris): insight into the common structural features of leguminous alpha-amylase inhibitors

The primary structures of two subunits of an alpha-amylase inhibitor (alpha AI-2) from a wild common bean (Phaseolus vulgaris) were revealed by a comparison of the amino acid sequence previously deduced from the nucleotide sequence with the amino- and carboxyl-terminal amino acid sequences determined by conventional methods. The polypeptide molecular weight of alpha AI-2 obtained by the light-scattering technique, considered together with the sequence molecular weights revealed for the subunits, indicated that alpha AI-2 has the subunit stoichiometry of an alpha 2 beta 2 complex. These structural features were closely similar to those recently elucidated for a white kidney bean (P. vulgaris) alpha-amylase inhibitor, which is quite different in the inhibitory specificity from alpha AI-2. The post-translational processing of the precursor glycoproteins to form the tetrameric structure appeared to require an Arg residue close to the processing site. Further, the proper associations of the subunits into the tetrameric structures seemed to be strictly controlled by a few amino acids on the subunit interfaces.

Delivery of liposome-sequestered hydrophobic proteins to lysosomes of normal and Batten disease cells

We have developed a method to deliver hydrophobic proteins such as ATP synthase subunit c and ubiquitin to lysosomes of PMN (polymorphonucleocytes) and fibroblasts. ATP synthase subunit c is stored in the lysosomes of various tissues in late infantile and juvenile forms of neuronal ceriod lipofuscinosis, also called Batten disease (BD). Whether this protein storage is due to an abbreviation in protein or in the lysosomal hydrolases of BD is still not clear. We have sequestered this protein and ubiquitin in the lipid membrane of liposomes. The liposomes coated with autologous heat-aggregated IgG or apolipoprotein E when presented to the PMN and fibroblasts, respectively, accumulated in the lysosomes. Both normal and BD PMN degraded 125I-ubiquitin; the rate of degradation was, however, slower by Batten PMN. These studies indicate that a hydrophobic molecule such as subunit c can be delivered to PMN and fibroblasts, and the sequestered proteins are accessible to lysosomal hydrolases. Therefore, this technique can be used to study the metabolism of highly hydrophobic proteins by lysosomes, especially the biochemical mechanism(s) of subunit c storage in BD.

Sequential excision of internal eliminated DNA sequences in the differentiating macronucleus of the hypotrichous ciliate Stylonychia lemnae

Elimination of internal eliminated sequences (IES) during macronuclear development of the hypotrichous ciliate Stylonychia lemnae was analyzed in one cluster of macronuclear precursor DNA sequences. The results indicate that IES elimination is a highly ordered process, it starts very early during macronuclear development and has only finished immediately before DNA fragmentation takes place. It occurs in distinct steps and the IES are eliminated in a specific order, where a defined IES is only removed after complete elimination of other IES. Transfection experiments clearly demonstrate that the structure of the IES itself is not sufficient for its correct excision but other cis-acting sequences or additional structural requirements are needed for IES elimination.

Murine alpha-macroglobulins demonstrate divergent activities as neutralizers of transforming growth factor-beta and as inducers of nitric oxide synthesis. A possible mechanism for the endotoxin insensitivity of the alpha2-macroglobulin gene knock-out mouse

alpha2-Macroglobulin null mice demonstrate increased resistance to endotoxin challenge (Umans, L., Serneels, L., Overbergh, L., Van Leuven, F., and Van den Berghe, H. (1995) J. Biol. Chem. 270, 19778-19785). We hypothesized that this phenotype might reflect the function of murine alpha2M (malpha2M) as a neutralizer of transforming growth factor-beta (TGF-beta) and inducer of nitric oxide synthesis in vivo. When incubated with wild-type mouse plasma, TGF-beta1 and TGF-beta2 bound only to malpha2M. Alternative TGF-beta-binding proteins were not detected in plasma from alpha2M(-/-) mice. Wild-type mouse plasma, but not plasma from alpha2M(-/-) mice, inhibited TGF-beta1 binding to TGF-beta receptors on fibroblasts. Purified malpha2M bound TGF-beta1 and TGF-beta2 with similar affinity; the KD values were 28 +/- 4 and 33 +/- 4 nM, respectively. Murinoglobulin, the second murine alpha-macroglobulin, bound both TGF-beta isoforms with 30-fold lower affinity. Malpha2M counteracted the activities of TGF-beta1 and TGF-beta2 in an endothelial cell growth assay. Malpha2M also induced NO synthesis when incubated with RAW 264.7 cells, an activity which probably results from the neutralization of autocrine TGF-beta activity. Human alpha2M induced NO synthesis comparably to malpha2M; however, MUG had no effect. These studies demonstrate that the ability to neutralize TGF-beta is a property of malpha2M, which is not redundant in the murine alpha-macroglobulin family or in murine plasma. Malpha2M is the only murine alpha-macroglobulin that promotes NO synthesis. The absence of malpha2M, in alpha2M(-/-) mice, may allow TGF-beta to more efficiently suppress excessive iNOS expression following endotoxin challenge.

Phylogeny and biogeography of Panax L. (the ginseng genus, araliaceae): inferences from ITS sequences of nuclear ribosomal DNA

Panax, the ginseng genus, is one of the most medicinally important genera in the Orient and demonstrates a classical eastern Asian and eastern North American disjunct distributional pattern. Sequences of the internal transcribed spacers (ITS) and the 5.8S coding region of the nuclear ribosomal DNA repeat were obtained for the 12 species of Panax to reconstruct phylogenetic relationships. Of the 2 eastern North American species, P. quinquefolius and P. trifolius, P. quinquefolius was suggested to be more closely related to the eastern Asian species in the ITS tree, while P. trifolius was phylogenetically isolated. Monophyly of the three medicinally most important species, P. ginseng, P. notoginseng, and P. quinquefolius, suggested by previous workers, was not supported by the ITS data. A close phylogenetic relationship between Panax and Aralia was supported. Several biogeographical implications were inferred: (1) two divergence events have produced the eastern Asian and eastern North American disjunct distribution in Panax, (2) no intercontinental species pairs are found in Panax; (3) a discrepancy between the sequence divergence pattern and the phylogenetic pattern was observed in Panax, suggesting the need for caution in using sequence divergence data alone in inferring biogeographical patterns; (4) the Himalayas and central and western China are the current centers of diversity of the ginseng genus; and (5) the low ITS sequence divergence and a close relationship among species in that region suggest that rapid evolutionary radiation may have created such a diversity of Panax in the Himalayas and in central and western China.

Human hepatic lipase subunit structure determination

Chinese hamster ovary cells were stably transfected with a human hepatic lipase (HL) cDNA. The recombinant enzyme was purified from culture medium in milligram quantities and shown to have a molecular weight, specific activity, and heparin affinity equivalent to HL present in human post-heparin plasma. The techniques of intensity light scattering, sedimentation equilibrium, and radiation inactivation were employed to assess the subunit structure of HL. For intensity light scattering, purified enzyme was subjected to size exclusion chromatography coupled to three detectors in series: an ultraviolet absorbance monitor, a differential refractometer, and a light scattering photometer. The polypeptide molecular weight (without carbohydrate contributions) was calculated using the measurements from the three detectors combined with the extinction coefficient of human HL. A single protein peak containing HL activity was identified and calculated to have a molecular mass of 107,000 in excellent agreement with the expected value for a dimer of HL (106.8 kDa). In addition, sedimentation equilibrium studies revealed that HL had a molecular mass (with carbohydrate contributions) of 121 kDa. Finally, to determine the smallest structural unit required for lipolytic activity, HL was subjected to radiation inactivation. Purified HL was exposed to various doses of high energy electrons at -135 degrees C; lipase activity decreased as a single exponential function of the radiation dose to less than 0.01% remaining activity. The target size of functional HL was calculated to be 109 kDa, whereas the size of the structural unit was determined to be 63 kDa. These data indicate that two HL monomer subunits are required for lipolytic activity, consistent with an HL homodimer. A model for active dimeric hepatic lipase is presented with implications for physiological function.

Size-exclusion chromatography with on-line light-scattering, absorbance, and refractive index detectors for studying proteins and their interactions

Techniques of using size-exclusion chromatography (SEC) with on-line light-scattering, uv absorbance, and refractive index detectors to characterize the polypeptide molecular weights of simple proteins or glycoproteins or to determine the stoichiometry of protein complexes are described. Two unique advantages of this approach over conventional SEC are that the molecular weight measurement is independent of elution position and can exclude the contributions from carbohydrates. When a protein or complex contains no carbohydrates, a two-detector method, i.e., light scattering combined with refractive index, can be used to calculate the molecular weight. When a protein contains carbohydrates, a three-detector method is used to calculate the molecular weight of polypeptide alone. Finally, a self-consistent three-detector method is used to determine the stoichiometry of a protein complex containing carbohydrates. Example applications for all these methodologies are described.

ErbB receptor activation, cell morphology changes, and apoptosis induced by anti-Her2 monoclonal antibodies

A panel of mAbs were generated against the purified soluble form of erbB2/Her2 receptor, corresponding to the extracellular region of the receptor, and examined for their ability to mimic the receptor ligand. Some of the mAbs strongly induced tyrosine phosphorylation of 180-185 kDa proteins, including not only Her2 but also Her3 and Her4 receptors, when they were expressed on the surface of breast cancer cells. These mAbs do not cross-react with Her3 or Her4 as demonstrated by competition study. Receptor phosphorylation was also observed with the cell lines transfected with Her2 or a chimeric receptor consisting of the extracellular domain of Her2 and the transmembrane and cytoplasmic domains of epidermal growth factor receptor. Selected mAbs were tested for their ability to change cell morphology, and one specific mAb, mAb74, induced cell morphology changes and apoptosis.

Oxidative stability and alpha-tocopherol retention in turkey burgers during refrigerated and frozen storage as influenced by dietary alpha-tocopheryl acetate

1. The effect of vitamin E (alpha-tocopheryl acetate) in turkey diets on the oxidative stability of raw and cooked turkey burgers and on the retention of alpha-tocopherol during refrigerated (4 degrees C) or frozen (-20 degrees C) storage was investigated. One hundred and two, one-day-old T-8s turkey poults were divided at random into 3 groups of 34 animals each and fed on either a basal diet (normal commercial turkey diet) supplemented with 20 mg alpha-tocopheryl acetate/kg (control) or fed an alpha-tocopherol supplemented diet containing 300 (E300) or 600 (E600) mg alpha-tocopheryl acetate/kg for 21 weeks. 2. Dietary supplementation with alpha-tocopheryl acetate significantly reduced TBARS numbers in both raw and cooked burgers during refrigerated and frozen storage. 3. The mean values of alpha-tocopherol in raw and cooked burgers stored at 4 degrees C did not change during storage. 4. In the case of both raw and cooked samples stored at -20 degrees C, the alpha-tocopherol values decreased from 5.67 to 3.54 and from 3.56 to 2.30 micrograms/g in the raw burgers from turkeys from the E600 and E300 treatments, respectively, after 4 months storage. The values decreased from 5.60 to 2.88 and from 3.29 to 1.85 micrograms/g in cooked burgers from turkeys from the E600 and E300 treatments, respectively, after 5 months storage.

Characterization of keratinocyte growth factor binding to heparin and dextran sulfate

Binding of keratinocyte growth factor (KGF) with heparin (molecular weight of 5000) and dextran sulfate (molecular weight of 8000) was studied using an online monitoring of size-exclusion chromatography with light scattering, refractive index, and uv absorbance detectors. This technique allows the determination of the molecular weight of KGF eluting as complexes with the above polymers. When mixtures of KGF with heparin were injected into the column, two peaks of heparin/KGF complexes were observed. The first peak corresponded to, on average, 3.4 KGF per complex and the second peak to an average of about 2 KGF per complex. These results suggest that the heparin/ KGF complex is heterogeneous, consisting of 1,2,3, and 4 KGF molecules per complex. To calculate the number of heparin molecules in these complexes, the rate of disappearance of free KGF was determined as heparin was added. The average number of KGF bound to 1 mol of heparin was calculated to be about 2 mol, suggesting that only one heparin molecule is present in these complexes. The heparin binding of two KGF mutants, i.e., (C1, 15S)KGF (with substitutions of serine for cysteines 1 and 15) and d28KGF (lacking 28 N-terminal amino acid residues), was essentially identical to that of the native sequence KGF. A similar experiment was carried out for KGF binding to dextran sulfate. The molecular weight of the complex corresponded to 2 to 2.6 KGF molecules per complex. The rate of disappearance of free KGF as the dextran sulfate added showed 2-3 mol of KGF bound to 1 mol of dextran sulfate, consistent with the idea that the complex contains only 1 dextran sulfate molecule.

Inguinal lymph node foreign body granulomas after placement of a silicone rubber (Silflex) implant of the first metatarsophalangeal joint

We describe a woman who developed foreign body granulomas 8 years after metatarsophalangeal (MTP) joint silicone rubber implantation for hallux rigidus. She developed overnight swelling and tenderness in the inguinal region on the ipsilateral side. Histological evaluation of the lymph node showed foreign body granulomas. Electron microscopy and dispersion x-ray analysis identified the foreign body material in the inguinal lymph node and fibrous capsule surrounding the implant as silicone. Foreign body granulomas of surrounding tissues and regional lymph nodes are infrequently reported postoperative complications in patients with small joint silicone rubber implants. A fractured or eroded implant surface attributed to wear is usually noted at prosthesis excision. Granulomas in normal or enlarged lymph nodes have been described in both symptomatic and asymptomatic patients, with intact or fractured prostheses. Many related joint and lymph node symptoms resolve with removal of the silicone rubber prosthesis.

Complete sequence, subunit structure, and complexes with pancreatic alpha-amylase of an alpha-amylase inhibitor from Phaseolus vulgaris white kidney beans

The complete amino acid sequence of a white kidney bean (Phaseolus vulgaris) alpha-amylase inhibitor (PHA-I), which is composed of two kinds of glycopolypeptide subunits, alpha and beta, was established by conventional methods. The polypeptide molecular weight of PHA-I determined by the light-scattering technique, considered together with the sequence molecular weights revealed for the subunits, indicated that PHA-I has the subunit stoichiometry of (alpha beta)2 complex. Inhibition test of PHA-I with increasing amounts of porcine pancreatic alpha-amylase (PPA) suggested that an inactive 2:1 complex is formed between PPA and PHA-I. In fact, two complexes differing from each other in the molar ratio of PPA to PHA-I were separated by gel filtration, and molecular weight estimation by the light-scattering technique confirmed that they are complexes of PHA-I with one or two PPA molecules. The binding of PPA to PHA-I appeared to follow simple binomial statistics, suggesting that two binding sites on PHA-I are independent and of high affinity for PPA.

Pulmonary malakoplakia in acquired immunodeficiency syndrome: an ultrastructural study of morphogenesis of Michaelis-Gutmann bodies

Malakoplakia is an unusual inflammatory reaction to a variety of infections, characterized by the accumulation of macrophages containing the target-like calcospherites, the Michaelis-Gutmann body (MGB). We report three patients with acquired immunodeficiency syndrome with pulmonary malakoplakia associated with Rhodococcus equi infection; two patients were diagnosed at autopsy and one by examination of a transbronchial biopsy specimen. All three patients had pulmonary bacterial cultures and light and electron microscopic examination. The patients were 33-, 41-, and 43-year old men, human immunodeficiency virus-positive for 2, 6, 8 years, respectively. The two patients diagnosed at autopsy had cavitary lesions, and the patient diagnosed by biopsy specimen had nodular lesions on chest radiographs. Histologically, the lungs had well-circumscribed areas of infiltration with benign macrophages with granular cytoplasm, scattered MGBs, and numerous gram-positive coccobacilli. Electron microscopic examination showed intracellular coccobacilli, from 990 X 702 to 972 X 648 nm in diameter, with thick, homogenous cell walls, trilaminar cytoplasmic membranes, and dense cytoplasm with from one to five vacuoles. Electron microscopic studies showed that the bacteria within the pulmonary macrophages had thicker cell walls, less prominent nucleoid areas, and more vacuoles than the bacteria in cultures from the sputum and blood. The mature MGB ultrastructurally had a concentric, trilaminate structure with central mineralized core and was without recognizable bacterial forms. Early MGBs, however, consisted of a circular, electron-dense core containing bacteria, ultrastructurally similar to the R. equi seen in the culture. Pulmonary malakoplakia in patients with the acquired immunodeficiency syndrome might thus represent an acquired macrophage dysfunction of the intracellular digestion of phagocytized bacteria. The bacteria within the macrophages, however, seemed to have thicker cell walls compared with those in culture, and thus might be protected from enzyme digestion. It seems that MGBs are formed around the undigested bacteria as an alternative pathway for bacterial destruction, because R. equi was identified within the cores of early MGBs but not the mature or late stage MGBs.

Dimerization of the extracellular domain of granuloycte-colony stimulating factor receptor by ligand binding: a monovalent ligand induces 2:2 complexes

Granulocyte-colony stimulating factor (G-CSF) binds to a specific cell surface receptor and induces signals for growth and differentiation in cells of granulocyte hematopoietic lineage. In order to understand how G-CSF binding initiates signals into these cells, we have studied its interactions with the entire extracellular domain of the receptor (sG-CSFR). The sG-CSFR was purified from CHO cell conditioned media with a G-CSF affinity column, resting in a preparation fully competent for ligand binding. However, when sG-CSFR was purified by conventional means, i.e., without affinity chromatography, only about half was competent. Therefore, all studies were carried out using affinity-purified material. The sG-CSFR exhibited a weak self-association into a dimer with a dissociation constant of 200microM in the absence of G-CSF. Addition of G-CSF dimerizes the receptor, with a preferred stoichiometry of 2 G-CSF molecules plus 2 receptors. Unexpectedly, receptor-receptor interactions rather than through two receptors binding to the same G-CSF molecule; i.e., G-CSF is a monovalent ligand. G-CSF binding to the receptor monomer occurs with high affinity. The binding of G-CSF also enhances the receptor-receptor dimerization; when G-CSF is bound to both receptors, dimerization is enhanced 2000-fold, while the interaction of a 1:1 receptor-ligand complex with a second ligand-free receptor is enhanced 80-fold. Thus, the mechanism of receptor dimerization is fundamentally different than that of related cytokine receptors such as growth hormone and erythropoietin receptors. Circular dichroic spectra showed a small but significant conformational change of receptor upon binding G-CSF. This is consistent with the idea that G-CSF binding alters the conformation of the receptor, resulting in an increase in receptor-receptor interactions.