How lymphocytes kill

Cytotoxic T lymphocytes and natural killer cells are potent killers of target cells. These lymphocytes have large cytoplasmic granules containing cytotoxic peptides and other factors. Several of these molecules have been isolated and their functions elucidated. These molecules may be directly involved in the killing of virus-infected and transformed cells as well as in the development of cell-mediated autoimmune disorders.

In vivo conversion of gamma-aminobutyric acid and 1,4-butanediol to gamma-hydroxybutyric acid in rat brain. Studies using stable isotopes

The formation of 4-[1,4-13C]hydroxybutyric acid ([13C]gamma-hydroxybutyric acid; [13C]GHB) in rat brain was studied following intracerebroventricular (i.c.v.) administration of either 4-[1,4-13C]aminobutyric acid ([13C]GABA or 1,4-[1,4-13C]butanediol ([13C]1,4-BD) to awake, freely moving animals. GHB and [13C]GHB were measured with a gas chromatographic mass spectrometric (GC/MS) technique designed to detect the lactone derivative of GHB with the acid or lactone being determined by conditions of tissue extraction. [13C]GHB was detected following i.c.v. administration of [13C]GABA with a turnover rate of 2.04 nmol/g tissue/hr and [13C]1,4-BD with a turnover rate of 1.4 nmol/g/hr. The formation of [13C]GHB from [13C]GABA was blocked by an inhibitor of GABA-transaminase, but this drug had no effect on the formation of [13C]GHB from [13C]1,4-BD. The latter pathway was also unaffected by alcohol dehydrogenase inhibitors, compounds which block this pathway in the periphery. Further, in the course of these experiments, naturally occurring endogenous gamma-butyrolactone (GBL) was detected in rat brain in a concentration of 200 pmol/g tissue weight, but lactonization in vivo of [13C]GHB formed from either labeled GABA or 1,4-BD was not demonstrated. These data confirm two separate pathways of synthesis for GHB in brain, demonstrate the presence of GBL in brain, and illustrate the utility of a new GC/MS technique for analysis of GHB and for GBL which does not involve extensive derivatization.

Purification of a ubiquitin protein peptidase from yeast with efficient in vitro assays

In eukaryotic cells ubiquitin is synthesized as a polyubiquitin protein or as a protein fused at the carboxyl terminus to other polypeptides. An enzyme activity, ubiquitin protein peptidase, has been proposed to process these precursors by cleaving the peptide bond between adjoining ubiquitin molecules or between ubiquitin and the fused peptides. Using the cleavage of a 35S-labeled yeast ubiquitin protein fused to a synthetic 38-residue peptide obtained by in vivo metabolic labeling in Escherichia coli in an expression system based on the interaction of bacteriophage T7 RNA polymerase and its promoter, it is possible to detect a processing activity in soluble yeast extract. The specificity of the cleavage suggests this activity could be the in vivo processing activity for various ubiquitin precursor proteins in yeast cells. A similarly labeled ubiquitin protein fused to one cysteine residue was also utilized to detect an activity capable of removing a single cysteine residue from ubiquitin in a soluble extract. Employing assays based on the cleavage of labeled ubiquitin protein fusions, a ubiquitin protein peptidase activity from Saccharomyces cerevisiae was purified about 15,000-fold to yield a protein mixture consisting of only a few protein species. The major protein band which comigrated with the activities in in vitro assays has an apparent molecular weight of 29,000 when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Two other protein species, about 20,000 and 10,000 in molecular weight, also comigrated with the in vitro activities throughout the purification procedure. Though our most purified protein fraction was shown to cleave various artificial ubiquitin protein fusions under our experimental conditions, it cannot cleave a ubiquitin dimer protein, suggesting the existence of functionally distinct ubiquitin protein peptidases. Our experimental protocol for preparing various labeled ubiquitin protein precursors provides a means to explore various processing enzymes existing in cells. The same protocol may also be adapted to prepare substrates for the study of other specific protein processing enzymes.

Perforin and serine esterase gene expression in stimulated human T cells. Kinetics, mitogen requirements, and effects of cyclosporin A

A pore-forming protein (PFP; perforin) and various serine esterases (SE) have been identified in the cytoplasmic granules of CTL and NK cells. Perforin and several SE have recently been cloned. Northern blotting analysis was performed here using cDNA probes specific for human perforin and two SE (SE 1/HS and SE 2/GB) to monitor the levels of specific mRNAs in mitogen-stimulated primary human T cells. These mRNAs were rapidly induced by IL-2 with optimal responses at 300 U/ml. After IL-2 treatment, mRNAs for perforin, SE 1, and SE 2 peaked at 12-24 h and decreased after 48 h. The three mRNAs were also induced in T cells treated with a combination of PMA plus lectin, OKT3 mAb, or plastic-adherent accessory cells. However, the induction induced by PMA/mitogen followed a slower kinetics, peaking at 48 h. In general, we found that SE 1 mRNA was more readily induced by IL-2, while SE 2 responded better to PMA/mitogen. Similar patterns of mRNA expression were observed for both unprimed T cells and PHA-primed T blasts. After stimulation with IL-2 and PMA/mitogen, the T8+ subset was shown to be the main producer of perforin, SE 1, and SE 2. Low levels of all three mRNAs, however, were also detected in the T4+ subset. The induction of all three mRNAs by either IL-2 or PMA/mitogen was partially blocked by the immunosuppressive drug cyclosporin A (CsA), but not by the biologically inactive analogue cyclosporin H. Together, these results point to some similarities and differences with upregulation of granule mediator mRNAs relative to lymphokine mRNAs. Both sets of genes require two signals for their induction by mitogens. In contrast to lymphokines, there is a strong response of granule mRNAs to IL-2, and the induction of these transcripts is only partially blocked by CsA.

Purification and Characterization of Pectinmethylesterase from Ficus awkeotsang Makino Achenes

Pectinmethylesterase from the pericarp of jelly fig (Ficus awkeotsang) achenes was extracted and purified to a specific activity of 289 micromole proton produced per minute per milligram protein. Pectinmethylesterase, a major protein with high specific activity in the crude extract, was monomeric with a molecular weight of 38,000. The enzyme preparation was stable in distilled water at 4 degrees C for at least 6 months, and at 60 degrees C for at least 10 minutes. This enzyme functioned optimally at pH 6.5 to 7.5 when the assay mixture contained no NaCl or at low NaCl concentration. The pH optimum shifted to lower pH as the NaCl concentration was increased. The K(m) value for pectin was 0.75 milligram per milliliter pectin, corresponding to a V(max) value of 310 micromoles per minute per milligram protein. Inhibition studies with antibodies indicated that jelly fig achene pectinmethylesterase and the two other pectinmethylesterases from orange and tomato were similar in their active site conformation; however, the surface determinants may be very different because no precipitation between anti-jelly fig pectinmethylesterase immune serum and the pectin methylesterase from orange and tomato could be observed in the double immunodiffusion analysis. Specific antisera raised against jelly fig achene pectinmethylesterase in a Western blot experiment also showed low similarity between jelly fig pectinmethylesterase with that from orange and tomato. This observation was also supported by the very low isoelectric point (pH 3.5) of jelly fig pectinmethylesterase, compared with high isoelectric points reported for most of the pectinmethylesterases. Amino acid composition and N-terminal sequence have been obtained. High homology of the N-terminal amino acid residues between jelly fig and tomato pectinmethylesterase (O Markovic, H Jornvall [1986] Eur J Biochem 158: 455-462) was observed. Pectinmethylesterase activity causes the release of protons from the deesterification of pectin such that a low pH environment is created, and this may be related to the cell growth. Pectinmethylesterase is not needed for jelly fig seed germination, however the gel formed from pectin and pectinmethylesterase may insure a water source for the germinating jelly fig seeds.

Thyrotropin-releasing hormone gene expression in normal thyroid parafollicular cells

The rat TRH gene encodes a 255-amino-acid precursor polypeptide, preproTRH, containing five copies of TRH and seven non-TRH peptides. Expression of this gene is well documented in the central nervous system, particularly in the hypothalamus. Thyroids also contain TRH immunoreactivity, but it is unknown whether this immunoreactivity results from expression of the TRH gene or from other genes encoding TRH-like products. Since the CA77 neoplastic parafollicular cell line expresses the TRH gene, we investigated whether TRH gene expression also occurs in normal thyroid parafollicular cells. Northern analysis of total thyroid RNA with a preproTRH-specific RNA probe identified a single hybridizing band the same size as authentic TRH mRNA found in hypothalamus and CA77 cells. Gel filtration analysis of thyroid extracts identified the same 7-kilodalton and 3-kilodalton species of immunoreactive preproTRH53-74 previously identified in hypothalamus and CA77 cells. Immunoreactive preproTRH115-151, not previously identified, was found in all three tissues. Part of this immunoreactivity comigrated with the synthetic preproTRH115-151 standard on gel filtration and reversed-phase HPLC. PreproTRH53-74 was localized to thyroid parafollicular cells by immunostaining. These findings demonstrate authentic TRH gene expression by normal rat thyroid parafollicular cells and establish the CA77 cell line as the only model system of a normal TRH-producing tissue. In addition to expanding the range of neuroendocrine peptides known to be produced by parafollicular cells, these results also suggest a potential paracrine regulatory role for TRH gene products within the thyroid.

Heterogeneity of granules of murine cytolytic T lymphocytes. Isolation of a homogeneous population of dense granules

A separation procedure based on Percoll gradient centrifugation is described here that allows enrichment for two main populations of granules, with average densities of 1.05 and 1.1 g/ml. The heavy-density granules, which comprise 5-20% of the total amount of membrane-lytic activity, are morphologically and biochemically more homogeneous than the light-density granules, which are contaminated with other subcellular organelles. A trypsin-like serine esterase activity, used in the past as a granule marker, was mainly found in the free cytosol and in the light-density fractions, while a small portion of this activity was associated with the heavy-density fractions. This enzyme marker is therefore not exclusively associated with granules and should not be used as the only granule marker.

Purified perforin induces target cell lysis but not DNA fragmentation

Rapid and extensive target cell DNA fragmentation is a unique characteristic of CTL-mediated killing. We studied the role of the granule pore-forming protein (PFP/perforin/cytolysin) of CTL in mediating lysis and DNA fragmentation of target cells. Perforin was isolated from murine CTL by sequential application of perforin-enriched granule fractions to four chromatographic columns: DEAE-Sepharose, Q-Sepharose, Polyanion SI, and Superose 12. Purified perforin was eluted as a single band of 70 kD in SDS-PAGE. While purified perforin produced potent lysis of a variety of target cells tested, it did not induce any measurable amount of DNA fragmentation. In parallel experiments, intact CTL produced marked DNA fragmentation of the same target cell populations. Our results suggest that perforin alone is not responsible for the DNA fragmentation observed during CTL-mediated killing and that other, as yet unknown, mediators or mechanisms are likely to be involved in the induction of target cell nuclear damage.

Parathyroid hormone potentiates the effect of insulin-like growth factor-I on bone formation

Insulin-like growth factor-I and parathyroid hormone are both known regulators of bone formation. In this study, human recombinant IGF-I and bovine PTH (1-34) and their combination were studied for their effects in vitro on the proliferation of embryonic chick osteoblast-like cells (osteoblasts) and in vivo on bone formation in normal rats. Osteoblasts from 17-day-old chick embryos were cultured in serum-free BGJb medium containing 0.1% bovine albumin. After 2 days, IGF-I and/or PTH were added. Twenty-four hours later [3H]thymidine incorporation into trichloroacetic acid precipitable material was quantified as an index of cell proliferation. This has previously been shown to reflect actual cell division. IGF-I at doses ranging from 0.85 to 13.6 nmol/l caused a dose-dependent increase in [3H]thymidine incorporation into osteoblasts. PTH alone (10 to 1000 pmol/l) had no significant effect. However, when combined with IGF-I, PTH potentiated the mitogenic effect of IGF-I and achieved statistical significance at 30 and 100 pmol/l (p less than 0.05). This potentiation was also studied in vivo. The right hind-limbs of rats weighing 150 g were infused intra-arterially by an osmotic minipump with graded doses of IGF-I (0.1 to 0.4 nmol/day) and/or PTH (0.27 nmol/day) for 7 days. The rate of trabecular bone apposition (formation) was measured by double tetracycline labelling and compared with the contralateral uninfused limb which acted as the control. Histomorphometric data revealed that neither IGF-I nor PTH alone had a significant effect on trabecular bone apposition rate compared with control limbs.(ABSTRACT TRUNCATED AT 250 WORDS)

The lymphocyte pore-forming protein perforin is associated with granules by a pH-dependent mechanism

A pore-forming protein (PFP, perforin or cytolysin) has been found in the cytoplasmic granules of cytotoxic T lymphocytes (CTL) and natural killer (NK) cells. Extraction of granules with high-salt buffers or by freezing-and-thawing results in the release of perforin, which occurs only when the buffer pH is above 7.0. While high-salt extraction and freezing-and-thawing of granules at low pH (below 7.0) do not result in perforin release, these treatments render granules susceptible to a subsequent incubation with low-salt buffers (pH 7-8) that then solubilizes perforin completely. Granules may thus have been made leaky by high-salt extraction or freezing-and-thawing that may occur regardless of the buffer pH, while dissociation of perforin from granules may be exquisitely pH-sensitive. Freezing-and-thawing intact CTL and NK cells in physiological buffers with pH in the range of 7-8 (but not below 7) also causes release of perforin activity to the cell supernatant, thus providing a simple procedure by which perforin activity can be quantitated in small cell samples. Our results suggest that during lymphocyte-mediated killing, the extracellularly released perforin may rapidly dissociate from granules as a result of pH change and, in the process, become cytolytically active.

Resistance of cytolytic lymphocytes to perforin-mediated killing. Induction of resistance correlates with increase in cytotoxicity

CTL and NK cells cultured in vitro are known to produce a cytolytic pore-forming protein (PFP, perforin) localized in their cytoplasmic granules. Using purified perforin, we showed here that both cloned CTL and primary killer cell populations, including allospecific CTL, NK/lymphokine-activated killer cells, and MHC-non-restricted CTL, were more resistant to perforin-mediated killing than other lymphocyte populations and cell types. Similar results were obtained with both murine and human cytolytic lymphocyte populations. Resistance of killer cells to perforin correlated in general with their cytolytic capability. Thus, cells that have acquired competence to kill after stimulation with Con A, IL-2, or leukocyte-conditioned medium, were also the more resistant cells. IL-2-independent CTL lines and hybridomas derived in our laboratories could be triggered to become cytotoxic and perforin resistant by short-term stimulation with various cytokines, indicating that the acquisition of resistance to perforin-mediated lysis was independent of cell proliferation. Activation of one IL-2-independent CTL line with IL-2 also resulted in enhanced production of perforin and in enhanced serine esterase activity. The acquisition of cell resistance to perforin by these IL-2-independent cell lines after activation with stimulatory reagents was independent of protein and RNA neosynthesis: emetine, cycloheximide, and actinomycin D, while effectively blocking the incorporation of [35S]methionine into cell proteins, did not affect the induced increase in perforin resistance.

Identification and characterization of a membrane-bound cytotoxin of murine cytolytic lymphocytes that is related to tumor necrosis factor/cachectin

Cytotoxic T lymphocytes (CTLs) kill their targets by a contact-dependent mechanism. We investigated the possibility that the CTL membranes themselves could exert direct cytotoxic activity. Murine CTLs that had been fixed with paraformaldehyde retained a slow cytotoxic activity toward various target cells that are also sensitive to another cytokine, tumor necrosis factor (TNF)/cachectin. This cytotoxic activity was neutralized by antibodies specific for TNF. Membrane fractions obtained from CTLs were cytotoxic to TNF-sensitive targets but not to several TNF-resistant cell lines. Immunoblot analysis revealed a membrane protein band of 50-60 kDa from CTLs that reacts with anti-TNF antibodies. The surface localization of this cytokine was further ascertained by flow cytometry, indirect immunofluorescence, and immunoelectron microscopy studies using TNF-specific antibodies. Radioiodination of CTL surface proteins followed by immunoprecipitation with anti-TNF antibodies confirmed the presence of a TNF-related cytokine in the plasma membranes of CTLs that migrated with an apparent molecular mass of 50-60 kDa under disulfide-reducing conditions. This cytokine can be removed from membranes by treatment with detergents but not with high-salt buffers, suggesting that it may be an integral membrane protein.

In vivo calvarial bone cell responses to dietary perturbations and the implications for mineral homeostasis

Calvariae from small animals have been an important source for in vitro studies of bone. However, few in vivo studies have been undertaken on quantitative cell changes in calvariae. In the present study of mineral perturbations, rats were first deprived of calcium. After 18 days endosteal osteoclasts and nuclei/osteoclast in the parietal bone had increased 120% (P less than 0.001) and 26% (P less than 0.001), respectively, the marrow space had increased 141% (P less than 0.001), and the bone area experienced a 49% decrease (P less than 0.001). This thinning and weakening of the calvaria was accompanied by a compensatory increase in the number of endosteal osteoblasts (297%, P less than 0.001). These rats were then replenished with calcium, and after 14 days the number of endosteal osteoclasts had decreased to 86% (P less than 0.001) below the control and the endosteal surface was almost completely covered by osteoblasts (866% above the control, P less than 0.001). Bone area was increased by 51% (P less than 0.01). Similarly, in calcium-deficient rats in the tibial diaphysis at the fibular junction, the number of endosteal osteoclasts and the medullary space increased 1606% (P less than 0.001) and 63% (P less than 0.001), respectively, which were accompanied by a 32% decrease (P less than 0.001) in cortical bone area. After calcium replenishment, most endosteal osteoclasts in the tibial diaphysis disappeared from the endosteal surface and were replaced by osteoblasts (increased 487%, P less than 0.001). These results indicate that changes in bone cell activity in response to calcium deficiency are similar in calvariae and long bones, and that mobilization of calcium from the calvaria during calcium deficiency occurs at the expense of the protective action of the calvaria. Therefore, long bones as well as membranous bones are apparently important for the maintenance of mineral homeostasis.

A clinical evaluation of sulbactam/ampicillin in the treatment of pediatric infections

We have treated 42 episodes of pediatric infections with sulbactam/ampicillin since 1987. Included were 9 cellulitis, 9 urinary tract infections, 5 cervical lymphadenitis, 4 meningitis, 2 thoracic empyema, 2 osteomyelitis, 2 sepsis, 1 furuncle, 1 perianal abscess, 1 dental abscess, 1 peritonsillitis, 1 salmonellosis, 1 shigellosis, 1 peritonitis, 1 suppurative thyroiditis, 1 infective endocarditis. Responsible pathogens were Escherichia coli in 8, Staphylococcus aureus in 6, Hemophilus influenzae in 2, Streptococcus pneumoniae in 3, Streptococcus viridans in 2, Staphylococcus epidermidis in 1, Bacteroides fragilis in 1, Salmonella D1 in 1, Shigella sonnei in 1, Klebsiella pneumoniae in 1, Enterobacter agglomerans in 1, Acinetobacter calcoaceticus in 1, Enterobacter cloacae in 1, group A beta-hemolytic streptococcus in 1, and polymicrobial infection in 4 cases. Thirty-nine out of 41 (95%) clinically evaluable patients cured and all (34/34) bacteriologically evaluable patients eradicated their pathogens after treatment with sulbactam/ampicillin. Side reactions were seen in five patients; one maculopapular skin rash, one hemolytic anemia, two diarrhea, and one liver function impairment plus leukopenia. All these reactions were transient and did not require interruption of therapy. These results indicate that sulbactam/ampicillin is safe and effective in the treatment of common pediatric infections beyond the neonatal period.

The structure of the mouse lymphocyte pore-forming protein perforin

Purified murine lymphocyte pore-forming protein (PFP or perforin) was partially sequenced. Oligonucleotides synthesized on the basis of this sequence information were used to screen a murine cytotoxic T lymphocyte (CTL) cDNA library. Seven clones were obtained, two of which were sequenced, providing full-length sequence information on PFP. Murine PFP (534 a.a.) is 68% identical to human PFP. Hydropathic analysis revealed a predominantly hydrophilic protein with some hydrophobic domains, including a region (a.a. 191-251) that could contain putative membrane-spanning domains. PFP is approx. 20% identical to human C7, C8 and C9 within a region encompassing 270 a.a., confirming previous immunological cross-reactivity studies. Northern blot analysis showed that expression of PFP but not of a serine esterase transcript is enhanced in a CTL line by antigen receptor-stimulation. Southern blot analysis of mouse genomic DNA indicated that PFP is encoded as a single-copy gene with the coding region contained within 10 kilobases of genomic DNA.

The aged rat model of ovarian hormone deficiency bone loss

Three studies were carried out. First, the effects of aging on the maturation of the female skeleton were assessed. Second, the hypothesis that has linked ovarian hormone deficiency bone loss to hypercalcemic suppression of the parathyroids leading to a decrease in 1,25-dihydroxyvitamin D synthesis and gut absorption of calcium was examined. Third, the effects of ovariectomy and a combination of ovarian hormone deficiency and low dietary calcium on bone and the calcium-regulating hormones were evaluated. After 6 months, ovariectomy and a low calcium diet independently decreased the density of the ilium, the femur, and the fourth lumbar vertebra as well as the calcium content of the latter two. The effects of the two treatment regimens were additive and more marked in the vertebral bone. Ovariectomy lowered serum calcitonin only in animals fed a normal diet and had no effect on serum PTH and vitamin D metabolites, while a low calcium diet caused a significant increase in serum 1,25-dihydroxyvitamin D. In both dietary regimens ovariectomy resulted in about a 30% decrease in intestinal calcium absorption. A low calcium diet increased morphometric indices of bone formation and bone resorption as did ovariectomy, with resorption exceeding formation. The discussion of our findings led to the conclusion that the aged rat model of ovarian hormone deficiency bone loss qualifies for serious consideration as a practical convenient cost-effective animal model for exploring aspects of the pathogenesis and treatment of postmenopausal bone loss.

Structural and metabolic integrity of sheep external intercostal muscle during extended culture

The objectives of this study were to examine the structural and metabolic integrity of isolated sheep external intercostal muscle bundles following variable lengths of preincubation (0 to 192 h). Samples of intact external intercostal muscle (10 to 15 g), with tendons attached, were prepared from growing wethers and maintained at their resting lengths during preincubation for 0 to 192 h. Protein synthesis (PS), protein degradation (PD), acetate oxidation and ultrastructural integrity of muscle samples were examined at 0 to 192 h, 0 to 96 h, 0 to 48 h and 0 to 96 h following isolation, respectively. Additionally, the effects of variable fetal calf serum (FCS) concentrations (0 to 20%; w/v) on PS and PD and acetate oxidation were examined. Rate of PS increased as preincubation time increased to 192 h; however, most of this increase was due to the proliferation of fibroblasts on the surface of the muscle sample. Addition of cytosine arabinoside to the incubation media prevented the fibroblast-dependent increase in PS; however, it did not entirely prevent the preincubation time-dependent increase in PS. Rate of PD increased greatly upon preincubation. The nitrogen balance of incubated muscles was negative at all times examined. Acetate oxidation was maintained through 12 h of preincubation and thereafter declined. Relatively normal myofibrillar structure was maintained through 48 h of preincubation; however, loss of mitochondrial integrity and dissolution of Z-disks at 48 h and at 96 h of preincubation were evident. Isolated tissues were able to respond to FCS concentration in medium following 48 h of preincubation.

Resistance of cytolytic lymphocytes to perforin-mediated killing. Lack of correlation with complement-associated homologous species restriction

CTL and NK cells resist self-mediated killing and lysis by their own pore-forming protein (PFP; perforin). Perforin, like C, lyses RBC. Efficient C-mediated lysis of RBC occurs when both C and RBC are from different species (homologous species restriction). A protective surface protein (C8-binding protein, homologous restriction factor) has been reported to mediate both homologous species restriction in C-dependent cytolysis and protection of some target cells against perforin-induced lysis. We show here that perforin, unlike C, lyses target cells across a variety of species, including the homologous one, while the same target cell populations resist the attack by homologous C. Perforin-containing extracts of CTL and LAK/NK cells from three species (rat, mouse, and human) and purified mouse perforin were tested against RBC from 10 different species, several nucleated target cell lines, and one primary cell population (thymocytes). While resisting lysis by homologous C, most of these cell types were lysed effectively by perforin without any homologous restriction pattern. CTL and NK cells, like other nucleated targets, are resistant to lysis by homologous but not heterologous C; however, these cell types are resistant to both homologous and heterologous perforin. Together, our results suggest that the protective mechanisms associated with C- and perforin-mediated lysis are distinct.

A semi-automated microassay for complement activity

A simple, automated microassay for the serum complement-dependent hemolytic activity is described here. In contrast to the traditional titration hemolysis assay, the new method depends on a single experimental step using a fixed volume of serum specimen and sheep erythrocytes. The assay is based on the change in light scattering properties of erythrocytes upon hemolysis. It relies on the spectrophotometric reading of microtiter well samples at 700 nm by using a microplate reader. The measured absorbance correlates proportionally with the extent of hemolysis. A good correlation between the results obtained using this technique and those obtained by the traditional CH50 titration method is observed. This simple procedure can be applied to the rapid, semi-quantitative diagnostic screening of complement activities of a large number of serum specimens.

Cloned cytotoxic T lymphocytes as target cells. II. Polarity of lysis revisited

The original polarity of lysis experiments suggested that CTL are themselves sensitive to whatever mechanism it is that CTL use to lyse their targets. This concept has placed certain limitations on possible mechanisms of lysis by CTL. Recently, we found in studies with cloned CTL as targets that cloned CTL are in fact highly resistant to lysis by other CTL, as well as to their cytotoxic granule proteins. We show here that although cloned CTL are extremely resistant to lysis by primary and cloned CTL, they are readily inactivated functionally by all primary CTL and by at least one CTL clone. Moreover, cloned CTL are also functionally inactivated by cytotoxic granule proteins. The activation of CTL, which we call inhibitin, is Ca2+ insensitive and distinct from hemolytic activity, and is, thus, unlikely to be perforin. These experiments suggest a possible alternative interpretation of the original polarity of lysis experiments.

Cloned cytotoxic T lymphocytes as target cells. II. Polarity of lysis revisited

The original polarity of lysis experiments suggested that CTL are themselves sensitive to whatever mechanism it is that CTL use to lyse their targets. This concept has placed certain limitations on possible mechanisms of lysis by CTL. Recently, we found in studies with cloned CTL as targets that cloned CTL are in fact highly resistant to lysis by other CTL, as well as to their cytotoxic granule proteins. We show here that although cloned CTL are extremely resistant to lysis by primary and cloned CTL, they are readily inactivated functionally by all primary CTL and by at least one CTL clone. Moreover, cloned CTL are also functionally inactivated by cytotoxic granule proteins. The activation of CTL, which we call inhibitin, is Ca2+ insensitive and distinct from hemolytic activity, and is, thus, unlikely to be perforin. These experiments suggest a possible alternative interpretation of the original polarity of lysis experiments.

Perforin-dependent and -independent pathways of cytotoxicity mediated by lymphocytes

There is little doubt at the present time that both perforin-dependent and -independent pathways are important in mediating the cytotoxicity associated with lymphocytes. The cell distribution of perforin, initially thought to include both CTL and NK cells, now must be viewed with caution because all previous biochemical studies on CTL have been conducted with cell lines propagated in long-term cultures in the presence of T cell growth factors (IL-2 and perhaps some still undefined factors). Under these conditions, CTL are known to assume a broader, NK-like specificity in target cell killing and may thus differ significantly from primary CTL generated in the body. Accordingly, perforin does not seem to be present in primary CTL activated directly through mixed lymphocyte reactions. It remains to be shown how primary CTL lyse target cells in vivo. Initial studies conducted in several laboratories have already provided some clues. It now seems that even in cultured, perforin-containing CTL, the perforin pathway is not an obligatory mechanism required for target cell killing. Other pathways, possibly involving TNF/lymphotoxin-like molecules, may play a direct role in this type of cytotoxicity. Other still unidentified factors now also need to be sought, including membrane polypeptides that may develop cytotoxicity directly upon cell contact and binding. Although from the studies reviewed here it is clear now that perforin has a more limited role in cell killing than originally proposed, it is still intriguing that it should share structural and functional homologies with complement proteins, drawing paradoxical analogies between two systems (the cellular and the humoral immune systems) which have evolved to become specialized to carry out separate immunological tasks. The cloning of the genes for perforin and for all the C proteins that comprise the MAC should reveal important information on how these genes originated and then diverged during evolution. The cellular distribution of other granule products, such as serine esterases, also must be viewed with caution. A serine esterase activity was initially thought to be CTL-specific. This information stimulated an intensive research activity in many laboratories that resulted in both the purification of a serine esterase family and the cloning of several serine esterase transcripts. It is becoming clear from recent evidence that this group of enzymes is not truly CTL-specific and therefore would not be expected to develop any function rendered absolutely necessary for cytolysis.(ABSTRACT TRUNCATED AT 400 WORDS)

Reactivation of inhibited bone acid phosphatase and its significance in bone histomorphometry

Despite biochemical demonstration of acid phosphatase (AcP) activation or reactivation in bone, few attempts have been made to show similar effects histochemically. Bones from growing rats, when fixed in 4% buffered formaldehyde at room temperature and demineralized in 5% formic acid, exhibited expected inactivation of AcP. The inhibited AcP, however, was reactivated by pre-incubation of sections for 1 hr at 37 degrees C in the following buffers: 0.2 M Tris, 0.2 M glycine, 0.2 M NaHCO3, or 0.1 M borax, as well as in alkaline water, but not in 0.2 M Na2HPO4 (all at pH 9). The reactivation was (a) site-specific (e.g., osteoclasts, osteoblasts, osteocytes, and cement lines), (b) temperature- and pH-dependent, (c) unaffected by OH- or SH--binding agents or by an alkaline phosphatase inhibitor, and (d) inhibited completely by 10 mM Na2HPO4. The reactivation process, much simplified and/or more effective than with the methods previously reported, was observed in all 83 human biopsy bones embedded in methyl methacrylate and in human bones stored in cold buffered formaldehyde for 7 months. This study demonstrates a unique method for reactivating and thus localizing the inhibited AcP in bones, and suggests possible applications in bone histomorphometry.

Identification, purification, and characterization of a mast cell-associated cytolytic factor related to tumor necrosis factor

The role of mast cells and mast-cell-derived factors in natural cytotoxic reactions was investigated. Cultured and freshly isolated murine mast cells are shown to be cytotoxic to WEHI-164 and YAC-1 targets in 18-hr viability assays but not in 4-hr assays. Here, we describe a cytotoxic factor in murine mast cells that is immunologically related to tumor necrosis factor (TNF). This TNF-like factor lyses WEHI-164 cells with a slow time course requiring 16-20 hr for the lytic reaction to complete. Antibodies specific for human and murine TNF and human lymphotoxin partially block mast cell lysis of WEHI-164 cells. These antibodies react on immunoblots with one major mast cell protein band of 50 kDa. Immunoblot analysis shows this factor in cloned and uncloned cultured mouse mast cells and in mature "connective tissue-type" mast cells freshly purified from rat or mouse peritoneal cavities. The amount of this factor is greatly enhanced in cells that have been stimulated with a combination of phorbol ester/concanavalin A or bacterial lipopolysaccharide. Subcellular fractionation analysis of mast cells with Percoll gradients reveals two pools of TNF-related cytotoxic activity that are associated with free cytosolic material and granule fractions. In contrast to cytotoxic T lymphocytes and natural killer cells, granule-enriched fractions of mast cells do not contain any hemolytic activity. The localization of the TNF-like molecule in mast cell granules may play a strategical role in the rapid delivery of this mediator to the target cell membrane following cell surface stimulation and degranulation.

A calcium- and perforin-independent pathway of killing mediated by murine cytolytic lymphocytes

Cytotoxic T lymphocytes have been thought to lyse cellular targets in the past by a calcium-dependent pathway. This notion was recently supported by the identification and purification of a pore-forming protein (perforin) from the granules of these cell types. Here, we show that perforin is absent from a number of cell lines that nevertheless display vigorous cytolytic activity toward target cells. The cytotoxic activity of eight murine CTL lines is completely or partially retained in the absence of calcium. The calcium-independent lytic activity is associated with two subcellular fraction peaks isolated by Percoll gradient centrifugation, e.g., a heavy density band migrating with granule markers and a lighter band corresponding to free cytosolic material. These results suggest a complex picture of lymphocyte-mediated killing involving probably multiple mechanisms and mediators that may operate in concert or independently in the delivery of the lethal hit.

Identification, isolation, and characterization of a novel cytotoxin in murine cytolytic lymphocytes

Murine cytotoxic T lymphocytes contain, in addition to the cytotoxic pore-forming protein perforin, another cytolytic factor localized in both cytoplasm and granules. Like perforin, this CTL cytotoxin lyses a variety of tumor cells; unlike perforin, it is stable in the presence of calcium, requires several hours to induce maximal lytic activity, and is antigenically related to the previously described tumor necrosis factor (TNF) and lymphotoxin (LT). However, it differs from TNF and LT in a number of biochemical and functional properties. TNF- and LT-specific cDNA probes did not hybridize with any CTL-specific message, indicating that the CTL cytotoxin is distinct from those two factors. It has an apparent Mr of 50 and 70 kd under reducing and nonreducing conditions, respectively, is secreted by secretagogue-stimulated CTLs, and causes DNA fragmentation in several targets, a phenomenon previously attributed to target cell damage by CTLs. These results suggest that killing by lymphocytes may encompass multiple mechanisms and polypeptides.

Resistance of cloned cytotoxic T lymphocytes to cell-mediated cytotoxicity

Cloned CTLs show an unusually high resistance to lysis by effector CTLs. Several cloned CTL lines in our laboratories are absolutely refractory to lysis by other cloned CTLs, either (a) directly, (b) in the presence of lectin, or (c) by PMA-induced CTLs. They can be lysed to some extent by primary CTL, although they are less than 5% as sensitive as target cells normally used to assay primary CTL lytic activity. Lysis of cloned CTLs by primary CTL effector cells is not enhanced by the presence of lectin, and cloned T cells are also highly resistant to lysis by primary lymphokine-activated killer cells. Cloned CTLs are highly resistant to lysis by isolated CTL granules that contain the membranolytic pore-forming protein (PFP or perforin), while non-CTL targets are highly susceptible to granule-mediated killing, indicating that cloned CTLs resist lysis not only at the intact effector cell level but also when soluble effector proteins are used. This resistance mechanism may explain how CTLs kill but spare themselves from being killed during the cytolytic event.

Increase in plasma phospholipid docosahexaenoic and eicosapentaenoic acids as a reflection of their intake and mode of administration

The fatty acid, docosahexaenoic acid (DHA, 22:6n-3), is a major constituent of red blood cell phosphatidylethanolamine and phosphatidylserine at birth but declines in all phospholipid classes following preterm delivery unless the diet contains DHA. A bolus of fish oil prevented declines in DHA of red cell phospholipids (phosphatidylethanolamine, phosphatidylcholine, and phosphatidylserine) during 4 to 6 wk of feeding, with red blood cell DHA indistinguishable from that of infants fed human milk. The amount of DHA fed was almost an order of magnitude greater than usually provided by human milk, however, suggesting poor absorption of fish oil by preterm infants. The purpose of these studies was to determine if uptake of fish oil DHA could be improved by dispersion in preterm formula. Since plasma phospholipids rapidly reflect changes in dietary fatty acid composition, DHA uptake was assessed by fatty acid analysis of plasma phosphatidylethanolamine and phosphatidylcholine. All groups receiving fish oil (both bolus and dispersed) demonstrated a rise in plasma phospholipid phosphatidylethanolamine DHA. Infants receiving 11 mg/kg/day DHA from dispersed fish oil, however, appeared to absorb as much or more as those receiving 71 mg/kg/day DHA in a bolus. The lower intake of DHA provided only 0.2% of total dietary fatty acids (human milk typically provides 0.1 to 0.3%). This study, in conjunction with an earlier report, demonstrates the feasibility of 1) long-term maintenance of red cell membrane DHA by its inclusion in infant formula and 2) DHA maintenance by "physiological" intakes of DHA; i.e. the amount provided by human milk.(ABSTRACT TRUNCATED AT 250 WORDS)

Production of granulocyte-stimulating and bone cell-modulating activities from a neutrophilia hypercalcemia-inducing murine mammary cancer cell line

We have previously shown that a transplantable murine tumor (CE mammary carcinoma) causes marked neutrophilia and excessive bone resorption in vivo. In order to understand the humoral mechanism of these tumor-induced phenomena, we successfully established a cell line (CE 816) and subsequently cloned CE mammary carcinoma cells in serum-free culture conditions. Cultured CE tumor cells continued to induce neutrophilia and hypercalcemia when they were transplanted back into mice. Conditioned medium (CM) prepared from the CE 816 cell line and control non-neutrophilia-inducing tumor cells were evaluated for stimulation of neutrophilic colony formation, embryonic bone cell proliferation, and bone resorption in vitro assays. Both the CE 816 and control tumor CM demonstrated colony-stimulating activity, but the CE 816 CM stimulated more neutrophilic colonies than the control tumor at all experimental conditions examined. The CE 816 CM demonstrated bone-resorbing activity but not control tumor CM. Both types of CM stimulated proliferation of embryonic bone cells. Production of colony-stimulating and bone-mitogenic activities was directly related to the tumor cell growth in vitro. CM prepared from four clones of CE tumor cells demonstrated both colony-stimulating and bone cell-mitogenic activities. These studies provided evidence that CE mammary carcinoma cells produce factors affecting granulopoiesis and bone cells in vitro, and these activities are clonal in origin.

A simplified technique for low temperature methyl methacrylate embedding

A simplified method for low temperature methyl methacrylate embedding with inhibited methyl methacrylate monomer is demonstrated using proper concentrations of benzoyl peroxide and N,N-dimethylaniline. The polymerized tissue blocks cut well and the tissue sections obtained show excellent acid phosphatase activity when demonstrated with the newly improved technique and Goldner's staining. Likewise, double tetracycline labels are well revealed by fluorescence microscopy.

Microelectronic sensors for simultaneous measurement of PO2 and pH

Sensors capable of simultaneous measurement of pH and PO2 in an aqueous solution have been fabricated in planar form using microelectronic technology. Separate potentiometric metal-metal oxide pH and three electrode amperemetric PO2 sensors have been fabricated together on a silicon chip with active surface of 2 x 3 mm. Rhodium-rhodium oxide electrodes operating in a cyclic voltammetry mode have also been studied and show sensitivity to both pH and PO2 in different regions of the voltage swept curve.

Development and reversibility of aluminum-induced bone lesion in the rat

We studied the effect of aluminum injections on bones of rats after intervals of 3, 6, and 9 weeks. To study reversibility, we allowed one group to recover for 3 weeks. Both weanling and adult rats were examined to determine the influence of age. The calcium, phosphate, creatinine, and parathyroid hormone levels were similar in aluminum-treated rats and controls. Aluminum could be seen by histochemical stain after 6 weeks, but at that time the bone was otherwise normal. By 9 weeks the bone formation (as measured by tetracycline labeling) in aluminum-treated rats was severely decreased on trabecular and endosteal surfaces. The periosteal surfaces showed normal formation. After 3 weeks of recovery, the bone formation rate in the young aluminum-treated rats was similar to that in the controls, although the serum and bone aluminum values had not significantly decreased. A higher percentage of aluminum was seen in the cement lines. In the adult rats, the bones had more stainable aluminum, and increased osteoid was noted along trabecular and periosteal surfaces. The doses of aluminum used in these rats greatly exceeded those that cause toxicity in humans; thus these findings may not directly apply to clinical practice. We conclude that aluminum administration can lead to decreased rates of bone formation in the rat, despite normal calcium level and renal function, and without decreased parathyroid hormone levels. The peritoneal route of administration could also have contributed to bone lesions by causing peritonitis, malabsorption, or both. Adult rats showed signs of early osteomalacia.(ABSTRACT TRUNCATED AT 250 WORDS)

The pore-forming protein (perforin) of cytolytic T lymphocytes is immunologically related to the components of membrane attack complex of complement through cysteine-rich domains

Structural, functional and immunological similarities between the ninth component of complement (C9) and the lymphocyte pore-forming protein (PFP, perforin) have recently been described (8-10). PFP is shown here to be immunologically related to all other components of the membrane attack complex (MAC) of human complement, namely, C5b-6, C7, C8, and C9. Polyclonal antibodies raised against purified human C5b-6, C7, C8, or C9 react with other components of the MAC and with mouse lymphocyte PFP. The antigenic epitopes shared by human complement proteins and mouse lymphocyte PFP are limited to cysteine-rich domains. Only complement proteins that have been reduced and alkylated elicit the production of crossreactive antibodies when used as immunogens. The nonreduced forms of complement components or lymphocyte PFP neither react with these antibodies nor give rise to crossreactive antibodies. The homologous domains of complement proteins and lymphocyte PFP may play related functions in their attachment to lipid membranes and assembly of membrane lesions.

Identification and characterization of a pore-forming protein of human peripheral blood natural killer cells

We show here that human peripheral blood NK cells contain a pore-forming protein (PFP) with an Mr of 70,000-72,000 that assembles structural lesions (with an average internal diameter of 150-170 A) and forms functional channels. The PFP was isolated by affinity chromatography from human NK cells, using a specific anti-C9 antiserum as the immunoadsorbent. The NK cells were isolated from PBL by positive or negative selection by indirect rosetting using a panel of monoclonal antibodies directed against different NK and T cell surface antigens. PFP was identified in NK cells freshly isolated and isolated from cultured PBL, both stimulated with interleukin 2, but not in NK cell-depleted lymphocytes. In planar bilayers, the channels formed by the NK cell-derived PFP are highly voltage resistant, with most channels persisting in the open state once they have inserted into the bilayer. The unit conductances of these channels range 0.3-1 nS in 0.1 M NaCl. The channels show poor selectivity for monovalent and divalent ions. The PFP is also released from human NK cells stimulated with the calcium ionophore A23187, suggesting that this protein, like the one produced by murine CTL lines, may be similarly secreted during cell-mediated killing. Its identification in primary human NK cell cultures indicates that this protein may play an active role in NK cell-mediated killing.

Isolation and characterization of a serine esterase from cytolytic T cell granules

Cytotoxic T lymphocytes and lymphocytes with NK-like activity contain a serine esterase activity which has been localized to their cytoplasmic granules by cytochemistry and subcellular fractionation studies. The serine esterase-specific inhibitor 3H-DFP labels two protein species in the granules. The two proteins, referred to as serine esterases 1 and 2 (SE 1 and SE 2), migrate with Mr of 34-36 kd and 28-30 kd, respectively, under reducing conditions. SE 1 shows trypsin-like activity and has been purified to apparent homogeneity. Under nonreducing conditions, SE 1 has an Mr of 60-66 kd, suggesting that it may consist of two disulfide-linked subunits of 34-36 kd each. SE 1 cleaves fibrin and casein, has a pl greater than 10, and optimal activity at pH 8. The substrate specificity of SE 2 is not known. The serine esterase activity is secreted by lymphocytes that have been stimulated with the calcium ionophore A23187. The serine esterases described here could play an active role in cell-mediated killing.

Extracellular release of lymphocyte cytolytic pore-forming protein (perforin) after ionophore stimulation

The cytolytic pore-forming protein (PFP, perforin) of lymphocyte granules has recently been isolated and characterized. The lytic activities expressed by both the isolated granules and the purified PFP require the presence of Ca2+. Here, we report on the extracellular release of PFP after stimulation of lymphocytes with the Ca2+ ionophore A23187, which degranulates the cells. The secreted protein associates with lipid to form structural and functional channels and supramolecular complexes that partially resist dissociation by sodium dodecyl sulfate and reducing agents. Immunoblots of the released material reveal positive identification with antibodies specific for mouse PFP and human complement component C9, indicating cross-reactivity between these two molecules. By using these specific antibodies as immunoadsorbents, the lymphocyte PFP has been affinity purified from the supernatant of stimulated cells. The extracellular release of PFP is associated with simultaneous formation of functional ion-nonselective channels with conductances of 550-600 pS in 0.15 M NaCl, as measured in planar model bilayers. In the absence of extracellular Ca2+, 15% of the maximal release activity is observed. Ca2+ appears to be required to elicit both secretion by lymphocytes and the assembly of the released PFP into tubular polymers. Similar secretion of PFP may occur during cell killing by lymphocytes, resulting in its assembly on target membranes to form tubular transmembrane lesions.

A mouse tumor-derived osteolytic factor stimulates bone resorption by a mechanism involving local prostaglandins production in bone

Culture medium which was conditioned by tissue of a CE mouse breast tumor in vitro contained dose-dependent osteolytic activity. The osteolytic activity was not soluble in dichloromethane and ethylacetate, indicating that it was not attributable to vitamin D metabolites or prostaglandins. However, breast tumor-conditioned medium stimulated production and release of prostaglandin E2 from mouse calvaria in vitro, and the stimulation of bone resorption in vitro by breast tumor-conditioned medium was blocked by a dose of indomethacin that prevented stimulation of mouse calvarial prostaglandin E2 production and release. The resorptive activity of parathyroid hormone (PTH) was not affected by the same dose of indomethacin, suggesting that the osteolytic factor was not PTH. This was further supported by observation that mouse kidney cell cAMP production was stimulated by PTH, but not by the aqueous phase of ethylacetate-extracted breast tumor-conditioned medium. In addition to osteolytic activity, breast tumor-conditioned medium contained a dose-dependent bone cell mitogenic activity, demonstrated by the stimulation of [3H]thymidine incorporation into trichloroacetic acid-insoluble macromolecules and a corresponding increase in bone cell number in monolayer cultures of bone cells. Breast tumor-conditioned medium also contained a dose-dependent transforming growth factor-(TGF-) like activity as defined by its ability to transform anchorage-dependent growth of nontransformed cells to anchorage-independent growth. The TGF in breast tumor-conditioned medium did not compete with epidermal growth factor (EGF) for EGF receptor binding, but its transforming activity was greatly enhanced by EGF, indicating that it was a beta-type TGF. Both the osteolytic and mitogenic activities were nondialyzable, sensitive to reducing agent, and not removable by dichloromethane and ethylacetate extractions. Furthermore, the TGF activity was not removed by ethylacetate extraction. Thus, the possibility that these activities in breast tumor-conditioned medium might be mediated by the same molecule must be considered. In summary, our data suggest that the CE mouse mammary carcinoma cells produce and secrete into the culture medium an osteolytic factor which is neither PTH nor prostaglandin and which stimulates local synthesis in bone of prostaglandin E2 which in turn increases bone resorption in vitro.

Gamma-hydroxybutyric acid binding sites in rat and human brain synaptosomal membranes

The binding of gamma-hydroxy[2,3-3H]butyric acid (GHB) was characterized in rat and human brain synaptosomal membranes. Binding was shown to be saturable, pH dependent, and linear with protein concentration. There was a distinct regional distribution of binding sites in both rat and human brain, with the hippocampus being the richest and the cerebellum the poorest, in density of [3H]GHB binding sites. Competition and saturation experiments revealed two different population of binding sites, a high-affinity site with a KD1 of 580 nM and a B max1 of 1.8 pmoles/mg protein and a low-affinity site with a KD2 of 2.3 microM and a B max2 of 11.3 pmoles/mg protein. [3H]GHB binding was not inhibited by gamma-aminobutyric acid (GABA), GABA receptor agonists, opiate antagonists or anticonvulsant drugs. These data suggest that GHB may play a role as a neurotransmitter or neuromodulator in brain independent of GABA.

Initiation of translation at internal AUG codons in mammalian cells

Initiation of translation of eukaryotic mRNAs typically occurs at the first AUG triplet from the 5' end of the message, although several notable exceptions have been described. Using vectors which efficiently express the gene encoding the surface antigen of hepatitis B virus in monkey cells, we have studied the consequences of inserting ATG triplets in all three reading frames upstream of the usual translational initiation codon of this gene. In agreement with the scanning model for eukaryotic translation initiation, these additional codons can severely depress the initiation of translation at the 'authentic' start codon, although the extent of inhibition depends on sequences flanking the upstream AUG. Such inhibition can, however, be at least partially suppressed by the presence of a translation termination codon in-frame with the upstream AUG. These results raise the possibility that mammalian ribosomes can reinitiate translation at an AUG codon after previously initiating, and terminating, at an upstream site.

Differential response in alveolar bone osteoclasts residing at two different bone sites

Using a histochemical method for demonstrating acid phosphatase activity, we have studied osteoclasts residing at two different bone sites in rat incisor alveolar bone, one at the endosteum and the other at the tooth socket, and compared the response of these osteoclasts to systemic changes. After 12 days of calcium (0%) or phosphorus (0.2%) deprivation, the number of osteoclasts/cross section at the endosteum increased 463% (P less than 0.001) and 103% (P less than 0.002), respectively. After 10 days of calcium or phosphorus replenishment, the number of osteoclasts at this bone site decreased to levels not significantly different from those in the control. In contrast, the number of osteoclasts at the incisor socket remained insignificantly changed throughout the experimental period. A similar osteoclast differential response was also observed in the alveolar bone surrounding the first molar tooth. After 12 days of calcium deprivation, the number of osteoclasts/mm bone surface increased 371% (P less than 0.001) at the endosteum but remained insignificantly changed at the first molar socket. These results suggest that an osteoclast differential response exists in alveolar bone and that the response may be of significance inasmuch as the major function of alveolar bone is to support the teeth. The work described here supports the concept of local as well as systemic regulation of bone metabolism to simultaneously perform the dual functions of mineral homeostasis and mechanical support.

Immobilized glucose oxidase in the potentiometric detection of glucose

Previous work has shown that glucose oxidase can be immobilized on platinum to give an electrode that responds potentiometrically to glucose over the clinically useful range of about 10-250 mg glucose/100 mL. The present studies were carried out with electrochemically pretreated platinum and with gold or porous graphite substituted for the platinum support. The presence of the enzyme gave a significantly enhanced potentiometric response over that obtained with the bare support for both the pretreated platinum and the porous graphite, but not with gold. However, with platinum the potentiometric response became more negative with increasing glucose concentration. With porous graphite, the potential changed in the positive direction as the glucose concentration was increased. Hysteresis was demonstrated for the platinum-enzyme electrode. Mass transfer measurements with a rotating ring-disc electrode (RRDE) showed measurable diffusional resistances to the transport of a model electroactive compound (potassium ferrocyanide) through a matrix of immobilized enzyme attached to the disc of the RRDE. These results are part of a larger study to define the source of the potentiometric response by examining the roles of the support and the mass transfer resistances through the immobilized enzyme matrix.

Regulation of bone repletion in rats subjected to varying low-calcium stress

Weanling Sprague-Dawley rats subjected to varying degrees of low-Ca dietary stress (depletion) showed graded increases in the rate of endosteal bone formation when normal dietary Ca was restored (repletion). There was a strong positive correlation between the rate of bone resorption in depletion and the rate of bone formation attained after 1 wk of repletion. However, bone formation declined rapidly within the first 4 wk of repletion, despite the persistence of a substantial endosteal bone volume deficit. Furthermore the medullary area (indicative of bone volume) did not by itself determine the bone formation rate. Bone volume in test groups was restored to control levels after 6 mo of repletion, and this result could be predicted by a kinetic analysis. Thus, although very high rates of formation in early repletion decline rapidly, smaller increments relative to controls must be sustained for long periods. Our data indicate that increased formation rats at all stages of repletion are a consequence of elevations in both osteoblast number and osteoblast activity.

Circulating immune complexes in cervical cancer patients as detected by C1q binding

In a retrospective study in women with cervical cancer, circulating immune complex levels were measured by radioimmunoprecipitation with 125I-C1q. Sera from 46 patients with cervical cancer and 35 normal controls were examined. Significantly higher levels of immune complexes were detected in cancer patients compared with controls. Mean value of binding capacity in patients was 49.8%, and by contrast, in the controls was 27.4% (two-tail test = 0). Increases in tumor mass were associated with high levels of circulating immune complexes. The presence of immune complexes in circulation statistically correlated with disease activity, however, the assay used still had limited value for diagnosis or aiding in therapeutic decisions. Nevertheless, the future holds promise for such uses.