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Results for “biological pathway”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Response of the water status of soybean to changes in soil water potentials controlled by the water pressure in microporous tubes

Water transport through a microporous tube-soil-plant system was investigated by measuring the response of soil and plant water status to step change reductions in the water pressure within the tubes. Soybeans were germinated and grown in a porous ceramic 'soil' at a porous tube water pressure of -0.5 kpa for 28 d. During this time, the soil matric potential was nearly in equilibrium with tube water pressure. Water pressure in the porous tubes was then reduced to either -1.0, -1.5 or -2.0 kPa. Sap flow rates, leaf conductance and soil, root and leaf water potentials were measured before and after this change. A reduction in porous tube water pressure from -0.5 to -1.0 or -1.5 kPa did not result in any significant change in soil or plant water status. A reduction in porous tube water pressure to -2.0 kPa resulted in significant reductions in sap flow, leaf conductance, and soil, root and leaf water potentials. Hydraulic conductance, calculated as the transpiration rate/delta psi between two points in the water transport pathway, was used to analyse water transport through the tube-soil-plant continuum. At porous tube water pressures of -0.5 to-1.5 kPa soil moisture was readily available and hydraulic conductance of the plant limited water transport. At -2.0 kPa, hydraulic conductance of the bulk soil was the dominant factor in water movement.

NASA Center JSC↗
NASA NTRS2001

Signal transduction mechanisms in plants: an overview

This article provides an overview on recent advances in some of the basic signalling mechanisms that participate in a wide variety of stimulus-response pathways. The mechanisms include calcium-based signalling, G-protein-mediated-signalling and signalling involving inositol phospholipids, with discussion on the role of protein kinases and phosphatases interspersed. As a further defining feature, the article highlights recent exciting findings on three extracellular components that have not been given coverage in previous reviews of signal transduction in plants, extracellular calmodulin, extracellular ATP, and integrin-like receptors, all of which affect plant growth and development.

Non-NASA Center↗
NASA NTRS1997

Plant responses to environmental stress: regulation and functions of the Arabidopsis TCH genes

Expression of the Arabidopsis TCH genes is markedly upregulated in response to a variety of environmental stimuli including the seemingly innocuous stimulus of touch. Understanding the mechanism(s) and factors that control TCH gene regulation will shed light on the signaling pathways that enable plants to respond to environmental conditions. The TCH proteins include calmodulin, calmodulin-related proteins and a xyloglucan endotransglycosylase. Expression analyses and localization of protein accumulation indicates that the potential sites of TCH protein function include expanding cells and tissues under mechanical strain. We hypothesize that at least a subset of the TCH proteins may collaborate in cell wall biogenesis.

Review, Tutorial↗
NASA NTRS2000

Complement activation promotes muscle inflammation during modified muscle use

Modified muscle use can result in muscle inflammation that is triggered by unidentified events. In the present investigation, we tested whether the activation of the complement system is a component of muscle inflammation that results from changes in muscle loading. Modified rat hindlimb muscle loading was achieved by removing weight-bearing from the hindlimbs for 10 days followed by reloading through normal ambulation. Experimental animals were injected with the recombinant, soluble complement receptor sCR1 to inhibit complement activation. Assays for complement C4 or factor B in sera showed that sCR1 produced large reductions in the capacity for activation of the complement system through both the classical and alternative pathways. Analysis of complement C4 concentration in serum in untreated animals showed that the classical pathway was activated during the first 2 hours of reloading. Analysis of factor B concentration in untreated animals showed activation of the alternative pathway at 6 hours of reloading. Administration of sCR1 significantly attenuated the invasion of neutrophils (-49%) and ED1(+) macrophages (-52%) that occurred in nontreated animals after 6 hours of reloading. The presence of sCR1 also reduced significantly the degree of edema by 22% as compared to untreated animals. Together, these data show that increased muscle loading activated the complement system which then briefly contributes to the early recruitment of inflammatory cells during modified muscle loading.

NASA Discipline Musculoskeletal↗
NASA NTRS1996

Preliminary Work in Obtaining Site-Directed Mutants of Hen Egg White Lysozyme

Protein crystal growth studies are recognized as a critical endeavor in the field of molecular biotechnology. The scientific applications of this field include the understanding of how enzymes function and the accumulation of accurate information of atomic structures, a key factor in the process of rational drug design. NASA has committed substantial investment and resources to the field of protein crystal growth and has conducted many microgravity protein crystal growth experiments aboard shuttle flights. Crystals grown in space tend to be larger, denser and have a more perfect habit and geometry. These improved properties gained in the microgravity environment of space result largely from the reduction of solutal convection, and the elimination of sedimentation at the growing crystal surface. Shuttle experiments have yielded many large, high quality crystals that are suitable for high resolution X-ray diffraction analysis. Examples of biologically important macromolecules which have been successfully crystallized during shuttle missions include: lysozyme, isocitrate lyase, gamma-interferon, insulin, human serum albumin and canavalin. Numerous other examples are also available. In addition to obtaining high quality crystals, investigators are also interested in learning the mechanisms by which the growth events take place. Crystallization experiments indicate that for the enzyme HEWL, measured growth rates do not follow mathematical models for 2D nucleation and dislocation-led growth of tetragonal protein crystals. As has been suggested by the laboratory of Marc L. Pusey, a possible explanation for the disagreement between observation and data is that HEWL tetraconal crystals form by aggregated units of lysozyme in supersaturated solutions. Surface measurement data was shown to fit very well with a model using an octamer unit cell as the growth unit. According to this model, the aggregation pathway and subsequent crystal growth is described by: monomer < ------ > dimer < ------- > tetramer < ------ > octamer < ------ > higher order. It is believed that multimer aggregation of lysozyme occurs by interaction at specific binding sites on the surface of the protein crystals. If the presence of discrete binding sites and the aggregation hypothesis is true, then it follows that the alteration of the binding site(s) should have significant effect on the measurements obtained during growth experiments. Site-directed mutagenesis allows the specific alteration of proteins by replacement, deletion or addition of specific amino acid residues. This report outlines the approach for this strategy and the progress made thus far toward that end.

Holmes, Leonard D.↗
NASA NTRS2003

A lignin-specific peroxidase in tobacco whose antisense suppression leads to vascular tissue modification

A tobacco peroxidase isoenzyme (TP60) was down-regulated in tobacco using an antisense strategy, this affording transformants with lignin reductions of up to 40-50% of wild type (control) plants. Significantly, both guaiacyl and syringyl levels decreased in essentially a linear manner with the reductions in lignin amounts, as determined by both thioacidolysis and nitrobenzene oxidative analyses. These data provisionally suggest that a feedback mechanism is operative in lignifying cells, which prevents build-up of monolignols should oxidative capacity for their subsequent metabolism be reduced. Prior to this study, the only known rate-limiting processes in the monolignol/lignin pathways involved that of Phe supply and the relative activities of cinnamate-4-hydroxylase/p-coumarate-3-hydroxylase, respectively. These transformants thus provide an additional experimental means in which to further dissect and delineate the factors involved in monolignol targeting to precise regions in the cell wall, and of subsequent lignin assembly. Interestingly, the lignin down-regulated tobacco phenotypes displayed no readily observable differences in overall growth and development profiles, although the vascular apparatus was modified.

NASA Program Fundamental Space Biology↗
NASA NTRS1990

DNA dynamics in aqueous solution: opening the double helix

The opening of a DNA base pair is a simple reaction that is a prerequisite for replication, transcription, and other vital biological functions. Understanding the molecular mechanisms of biological reactions is crucial for predicting and, ultimately, controlling them. Realistic computer simulations of the reactions can provide the needed understanding. To model even the simplest reaction in aqueous solution requires hundreds of hours of supercomputing time. We have used molecular dynamics techniques to simulate fraying of the ends of a six base pair double strand of DNA, [TCGCGA]2, where the four bases of DNA are denoted by T (thymine), C (cytosine), G (guanine), and A (adenine), and to estimate the free energy barrier to this process. The calculations, in which the DNA was surrounded by 2,594 water molecules, required 50 hours of CRAY-2 CPU time for every simulated 100 picoseconds. A free energy barrier to fraying, which is mainly characterized by the movement of adenine away from thymine into aqueous environment, was estimated to be 4 kcal/mol. Another fraying pathway, which leads to stacking between terminal adenine and thymine, was also observed. These detailed pictures of the motions and energetics of DNA base pair opening in water are a first step toward understanding how DNA will interact with any molecule.

NASA Discipline Number 52-20↗
NASA NTRS2018

Carbon-Nitrogen Coupling Under Three Schemes of Model Representation: A Traceability Analysis

The interaction between terrestrial carbon (C) and nitrogen (N) cycles has been incorporated into more and more land surface models. However, the scheme of C-N coupling differs greatly among models, and how these diverse representations of C-N interactions will affect C-cycle modeling remains unclear. In this study, we explored how the simulated ecosystem C storage capacity in the terrestrial ecosystem (TECO) model varied with three different commonly used schemes of C-N coupling. The three schemes (SM1, SM2, and SM3) have been used in three different coupled C-N models (i.e., TECO-CN, CLM 4.5, and O-CN, respectively). They differ mainly in the stoichiometry of C and N in vegetation and soils, plant N uptake strategies, down regulation of photosynthesis, and the pathways of N import. We incorporated the three C-N coupling schemes into the C-only version of the TECO model and evaluated their impacts on the C cycle with a traceability framework. Our results showed that all three of the C-N schemes caused significant reductions in steady-state C storage capacity compared with the C-only version with magnitudes of −23%, −30%, and −54% for SM1, SM2, and SM3, respectively. This reduced C storage capacity was mainly derived from the combined effects of decreases in net primary productivity (NPP; −29%, −15%, and −45%) and changes in mean C residence time (MRT; 9%, −17%, and −17%) for SM1, SM2, and SM3, respectively. The differences in NPP are mainly attributed to the different assumptions on plant N uptake, plant tissue C : N ratio, down regulation of photosynthesis, and biological N fixation. In comparison, the alternative representations of the plant vs. microbe competition strategy and the plant N uptake, combined with the flexible C : N ratio in vegetation and soils, led to a notable spread in MRT. These results highlight the fact that the diverse assumptions on N processes represented by different C-N coupled models could cause additional uncertainty for land surface models. Understanding their difference can help us improve the capability of models to predict future biogeochemical cycles of terrestrial ecosystems.

Du, Zhenggang↗
NASA NTRS2003

Photic and circadian regulation of retinal melatonin in mammals

Several studies have established that melatonin synthesis occurs in the retina of vertebrates, including mammals. In mammals, a subpopulation of photoreceptors (probably the cones) synthesize melatonin. Melatonin synthesis in the retina is elevated at night and reduced during the day in a fashion similar to events in the pineal gland. Both the MT1 and MT2 melatonin receptors are present in the retina and retinal melatonin does not contribute to circulating levels, suggesting that retinal melatonin acts locally as a neurohormone and/or neuromodulator. Melatonin synthesis in the retina of mammals is under the control of a circadian oscillator, and circadian rhythms in melatonin synthesis and/or release have been described for several species of mammals. These rhythms are present in vivo, persist in vitro, are entrained by light and are temperature compensated. The cloning of the gene responsible for the synthesis of the enzyme arylalkylamine N-acetyltransferase (the key enzyme in the melatonin biosynthetic pathway) has allowed studies of the molecular mechanisms responsible for the generation of retinal melatonin rhythmicity. The present review focuses on the cellular and molecular mechanisms that regulate melatonin synthesis. In particular, we discuss how the photic environment and the circadian clock interact in determining melatonin levels, in addition to the role that melatonin plays in retinal physiology.

NASA Discipline Space Human Factors↗
NASA NTRS1997

The ethylene response pathway in Arabidopsis

The simple gas ethylene influences a diverse array of plant growth and developmental processes including germination, senescence, cell elongation, and fruit ripening. This review focuses on recent molecular genetic studies, principally in Arabidopsis, in which components of the ethylene response pathway have been identified. The isolation and characterization of two of these genes has revealed that ethylene sensing involves a protein kinase cascade. One of these genes encodes a protein with similarity to the ubiquitous Raf family of Ser/Thr protein kinases. A second gene shows similarity to the prokaryotic two-component histidine kinases and most likely encodes an ethylene receptor. Additional elements involved in ethylene signaling have only been identified genetically. The characterization of these genes and mutants will be discussed.

Non-NASA Center↗
NASA NTRS2004

Computation Molecular Kinetics Model of HZE Induced Cell Cycle Arrest

Cell culture models play an important role in understanding the biological effectiveness of space radiation. High energy and charge (HZE) ions produce prolonged cell cycle arrests at the G1/S and G2/M transition points in the cell cycle. A detailed description of these phenomena is needed to integrate knowledge of the expression of DNA damage in surviving cells, including the determination of relative effectiveness factors between different types of radiation that produce differential types of DNA damage and arrest durations. We have developed a hierarchical kinetics model that tracks the distribution of cells in various cell phase compartments (early G1, late G1, S, G2, and M), however with transition rates that are controlled by rate-limiting steps in the kinetics of cyclin-cdk's interactions with their families of transcription factors and inhibitor molecules. The coupling of damaged DNA molecules to the downstream cyclin-cdk inhibitors is achieved through a description of the DNA-PK and ATM signaling pathways. For HZE irradiations we describe preliminary results, which introduce simulation of the stochastic nature of the number of direct particle traversals per cell in the modulation of cyclin-cdk and cell cycle population kinetics. Comparison of the model to data for fibroblast cells irradiated photons or HZE ions are described.

Cucinotta, Francis A.↗
NASA NTRS2015

VIIP: Central Nervous System (CNS) Modeling

Current long-duration missions to the International Space Station and future exploration-class missions beyond low-Earth orbit expose astronauts to increased risk of Visual Impairment and Intracranial Pressure (VIIP) syndrome. It has been hypothesized that the headward shift of cerebrospinal fluid (CSF) and blood in microgravity may cause significant elevation of intracranial pressure (ICP), which in turn may then induce VIIP syndrome through interaction with various biomechanical pathways. However, there is insufficient evidence to confirm this hypothesis. In this light, we are developing lumped-parameter models of fluid transport in the central nervous system (CNS) as a means to simulate the influence of microgravity on ICP. The CNS models will also be used in concert with the lumped parameter and finite element models of the eye described in the related IWS works submitted by Nelson et al., Feola et al. and Ethier et al.

intraocular pressure↗
NASA NTRS2002

Parathyroid hormone-dependent signaling pathways regulating genes in bone cells

Parathyroid hormone (PTH) is an 84-amino-acid polypeptide hormone functioning as a major mediator of bone remodeling and as an essential regulator of calcium homeostasis. PTH and PTH-related protein (PTHrP) indirectly activate osteoclasts resulting in increased bone resorption. During this process, PTH changes the phenotype of the osteoblast from a cell involved in bone formation to one directing bone resorption. In addition to these catabolic effects, PTH has been demonstrated to be an anabolic factor in skeletal tissue and in vitro. As a result, PTH has potential medical application to the treatment of osteoporosis, since intermittent administration of PTH stimulates bone formation. Activation of osteoblasts by PTH results in expression of genes important for the degradation of the extracellular matrix, production of growth factors, and stimulation and recruitment of osteoclasts. The ability of PTH to drive changes in gene expression is dependent upon activation of transcription factors such as the activator protein-1 family, RUNX2, and cAMP response element binding protein (CREB). Much of the regulation of these processes by PTH is protein kinase A (PKA)-dependent. However, while PKA is linked to many of the changes in gene expression directed by PTH, PKA activation has been shown to inhibit mitogen-activated protein kinase (MAPK) and proliferation of osteoblasts. It is now known that stimulation of MAPK and proliferation by PTH at low concentrations is protein kinase C (PKC)-dependent in both osteoblastic and kidney cells. Furthermore, PTH has been demonstrated to regulate components of the cell cycle. However, whether this regulation requires PKC and/or extracellular signal-regulated kinases or whether PTH is able to stimulate other components of the cell cycle is unknown. It is possible that stimulation of this signaling pathway by PTH mediates a unique pattern of gene expression resulting in proliferation in osteoblastic and kidney cells; however, specific examples of this are still unknown. This review will focus on what is known about PTH-mediated cell signaling, and discuss the established or putative PTH-regulated pattern of gene expression in osteoblastic cells following treatment with catabolic (high) or anabolic (low) concentrations of the hormone.

NASA Discipline Musculoskeletal↗
NASA NTRS2004

Did the Pre-RNA World Rest Upon DNA Molecules?

The isolation of a DNA sequence that catalyzes the ligation of oligodeoxynucleotides via the formation of 3' - 5' phosphodiester linkage significance in selection experiments has been reported. Ball recently used this to discuss the possibility that natural DNA molecules may have formed in the primitive Earth leading to the origin of life. As noted by Ferris and Usher, if metabolic pathways evolved backwards, it could be argued that the biosynthesis of 2-deoxyribose from ribose suggests that RNA came from DNA. As summarized elsewhere, there are several properties of deoxyribose which could be interpreted to support the possibility that DNA-like molecules arose prior to the RNA world. For example, 2-deoxyribose is slightly more soluble than ribose (which may have been an advantage in a drying pool scenario), may have been more reactive under possible prebiotic conditions (it forms a nucleoside approx. 150 times faster than ribose with the alternative base urazole at 25 C), while it decomposes in solution (approximately 2.6 times more slowly than ribose at 100 C). Other advantages of DNA over RNA are that it has one fewer chiral center, has a greater stability at the 8.2 pH value of the current oceans, and does not has the 2'5' and 3'5' ambiguity in polymerizations. Yet, there is strong molecular biological and biochemical evidence that RNA was featured in the biology well before the last common ancestor. The presence of sugar acids, including both ribo- and deoxysugar acids, in the 4.6 Ga old Murchison meteorite suggest that both may have been available in the primitive Earth, derived from the accretion of extraterrestrial sources and/or from endogenous processes involving formaldehyde and its derivatives. However, the abiotic synthesis of deoxyribose, ribose, and other sugars from glyceraldehyde and acetaldehyde under alkaline conditions is inefficient and unespecific. Although sugars are labile compounds, the role of cyanamide or borate minerals in the stabilization of the cyclic forms of ribose and other pentoses has recently been demonstrated. Nonetheless, the assumption either RNA or DNA was the first genetic material needs to be supplemented by laboratory models demonstrating that the prebiotic synthesis of activated beta-D-(deoxy)ribonucleotides and their polymers was feasible. As of today such evidence is lacking, and there is no convincing synthesis of any nucleotide, since all model experiments produce complex mixtures of products in which there is no preferential synthesis of chiral D-nucleotides. This strongly suggests that both DNA and RNA may have been preceded by pairing structures much simpler than extant nucleic acids. It is doubtful that DNA molecules, or indeed other (de0xy)ribofuranoid oligonucleotides formed the basis of these as yet undescribed pre-RNA worlds.

Lazcano, Antonio↗
NASA NTRS2002

Shear stress stimulates phosphorylation of endothelial nitric-oxide synthase at Ser1179 by Akt-independent mechanisms: role of protein kinase A

Recently, we have shown that shear stress stimulates NO(*) production by the protein kinase B/Akt (Akt)-dependent mechanisms in bovine aortic endothelial cells (BAEC) (Go, Y. M., Boo, Y. C., Park, H., Maland, M. C., Patel, R., Pritchard, K. A., Jr., Fujio, Y., Walsh, K., Darley-Usmar, V., and Jo, H. (2001) J. Appl. Physiol. 91, 1574-1581). Akt has been believed to regulate shear-dependent production of NO(*) by directly phosphorylating endothelial nitric-oxide synthase (eNOS) at the Ser(1179) residue (eNOS-S(1179)), but a critical evaluation using specific inhibitors or dominant negative mutants (Akt(AA) or Akt(AAA)) has not been reported. In addition, other kinases, including protein kinase A (PKA) and AMP kinase have also shown to phosphorylate eNOS-S(1179). Here, we show that shear-dependent phosphorylation of eNOS-S(1179) is mediated by an Akt-independent, but a PKA-dependent, mechanism. Expression of Akt(AA) or Akt(AAA) in BAEC by using recombinant adenoviral constructs inhibited phosphorylation of eNOS-S(1179) if cells were stimulated by vascular endothelial growth factor (VEGF), but not by shear stress. As shown before, expression of Akt(AA) inhibited shear-dependent NO(*) production, suggesting that Akt is still an important regulator in NO production. Further studies showed that a selective inhibitor of PKA, H89, inhibited shear-dependent phosphorylation of eNOS-S(1179) and NO(*) production. In contrast, H89 did not inhibit phosphorylation of eNOS-S(1179) induced by expressing a constitutively active Akt mutant (Akt(Myr)) in BAEC, showing that the inhibitor did not affect the Akt pathway. 8-Bromo-cAMP alone phosphorylated eNOS-S(1179) within 5 min without activating Akt, in an H89-sensitive manner. Collectively, these results demonstrate that shear stimulates phosphorylation of eNOS-S(1179) in a PKA-dependent, but Aktindependent manner, whereas the NO(*) production is regulated by the mechanisms dependent on both PKA and Akt. A coordinated interaction between Akt and PKA may be an important mechanism by which eNOS activity is regulated in response to physiological stimuli such as shear stress.

Non-NASA Center↗
NASA NTRS1993

Water uptake by growing cells: an assessment of the controlling roles of wall relaxation, solute uptake, and hydraulic conductance

Growing plant cells increase in volume principally by water uptake into the vacuole. There are only three general mechanisms by which a cell can modulate the process of water uptake: (a) by relaxing wall stress to reduce cell turgor pressure (thereby reducing cell water potential), (b) by modifying the solute content of the cell or its surroundings (likewise affecting water potential), and (c) by changing the hydraulic conductance of the water uptake pathway (this works only for cells remote from water potential equilibrium). Recent studies supporting each of these potential mechanisms are reviewed and critically assessed. The importance of solute uptake and hydraulic conductance is advocated by some recent studies, but the evidence is indirect and conclusions remain controversial. For most growing plant cells with substantial turgor pressure, it appears that reduction in cell turgor pressure, as a consequence of wall relaxation, serves as the major initiator and control point for plant cell enlargement. Two views of wall relaxation as a viscoelastic or a chemorheological process are compared and distinguished.

Non-NASA Center↗
NASA NTRS2003

An in silico assessment of gene function and organization of the phenylpropanoid pathway metabolic networks in Arabidopsis thaliana and limitations thereof

The Arabidopsis genome sequencing in 2000 gave to science the first blueprint of a vascular plant. Its successful completion also prompted the US National Science Foundation to launch the Arabidopsis 2010 initiative, the goal of which is to identify the function of each gene by 2010. In this study, an exhaustive analysis of The Institute for Genomic Research (TIGR) and The Arabidopsis Information Resource (TAIR) databases, together with all currently compiled EST sequence data, was carried out in order to determine to what extent the various metabolic networks from phenylalanine ammonia lyase (PAL) to the monolignols were organized and/or could be predicted. In these databases, there are some 65 genes which have been annotated as encoding putative enzymatic steps in monolignol biosynthesis, although many of them have only very low homology to monolignol pathway genes of known function in other plant systems. Our detailed analysis revealed that presently only 13 genes (two PALs, a cinnamate-4-hydroxylase, a p-coumarate-3-hydroxylase, a ferulate-5-hydroxylase, three 4-coumarate-CoA ligases, a cinnamic acid O-methyl transferase, two cinnamoyl-CoA reductases) and two cinnamyl alcohol dehydrogenases can be classified as having a bona fide (definitive) function; the remaining 52 genes currently have undetermined physiological roles. The EST database entries for this particular set of genes also provided little new insight into how the monolignol pathway was organized in the different tissues and organs, this being perhaps a consequence of both limitations in how tissue samples were collected and in the incomplete nature of the EST collections. This analysis thus underscores the fact that even with genomic sequencing, presumed to provide the entire suite of putative genes in the monolignol-forming pathway, a very large effort needs to be conducted to establish actual catalytic roles (including enzyme versatility), as well as the physiological function(s) for each member of the (multi)gene families present and the metabolic networks that are operative. Additionally, one key to identifying physiological functions for many of these (and other) unknown genes, and their corresponding metabolic networks, awaits the development of technologies to comprehensively study molecular processes at the single cell level in particular tissues and organs, in order to establish the actual metabolic context.

NASA Program Fundamental Space Biology↗
NASA NTRS1995

Lipopolysaccharide modulation of a CD14-like molecule on porcine alveolar macrophages

Cluster of differentiation antigen 14 (CD14) functions as a receptor for lipopolysaccharide (LPS) LPS-binding protein (LBP) complexes. Because LPS has varying effects on CD14 expression in vitro, we evaluated CD14 expression in response to LPS with a fully differentiated macrophage phenotype, the alveolar macrophage. By using flow microfluorometric analysis and a radioimmunoassay with an anti-human CD14 monoclonal antibody (My4) that cross-reacts with porcine CD14, we found that macrophages stimulated with LPS for 24 h exhibited a two- to fivefold increase in CD14-like antigen compared with unstimulated cells. At low concentrations of LPS, up-regulation of the CD14-like antigen was dependent on serum; at higher concentrations of LPS, serum was not required. In the absence of serum a 10-fold higher dose of LPS (10 ng/ml) was required to increase CD14-like expression. In addition, LPS-induced CD14-like up-regulation correlated with secretion of tumor necrosis factor-alpha, regardless of serum concentration. Blockade with My4 antibody significantly inhibited LPS-induced tumor necrosis factor-alpha secretion at 1 ng/ml of LPS. However, inhibition decreased as we increased the LPS concentration, suggesting the existence of CD14-independent pathways of macrophage activation in response to LPS. Alternatively, My4 may have a lower affinity for the porcine CD14 antigen than LPS, which may have only partially blocked the LPS-LBP binding site at high concentrations of LPS. Therefore, these data suggest that LPS activation of porcine alveolar macrophages for 24 h increased CD14-like receptor expression. The degree of CD14-like up-regulation was related to LPS concentration, however, activation did not require the presence of serum at high concentrations of LPS.

Non-NASA Center↗