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Biomedical subjects

L A Lewis

Publications and source records attributed to L A Lewis.

At least 19 recordsLinked to original sources
PubMed2002

Northern bobwhite and lead shot deposition in an upland habitat.

We estimated total lead shotshell pellets expended, resultant pellet availability near soil surface, and the frequency of pellet ingestion by northern bobwhites ( Colinus virginianus) attributable to nearly a quarter century of bobwhite hunting on a 202-ha upland habitat at Tall Timbers Research Station, Leon County, Florida. A total of 7776 shots were fired, resulting in the expenditure of approximately 4.5 million pellets (approximately 22519/ha). Sixteen of 235 (6.8%) soil samples collected in 1989 and 1992 contained one or two pellets. Soil samples indicated that approximately 7800 pellets/ha (about 35% of the projected 24-year deposition) were within 2.54 cm of the soil surface. Pellet ingestion by bobwhites was evaluated by examining 241 gizzards collected from 1989-92. Three bobwhites (1.3%) had ingested pellets ( x = 1.3 pellets). No instances of suspected lead poisoning were noted in bobwhites over the 24-year period. Sport hunting of wild bobwhite populations on upland habitats appears to produce a low potential for lead poisoning compared to lead deposition in association with waterfowl and dove hunting.

Animals↗
PubMed2002

Interactions of haemoglobin with the Neisseria meningitidis receptor HpuAB: the role of TonB and an intact proton motive force.

We have characterized the interaction of the Neisseria meningitidis TonB-dependent receptor HpuAB with haemoglobin (Hb). Protease accessibility assays indicated that HpuA and HpuB are surface exposed, HpuB interacts physically with HpuA, and TonB energization affects the conformation of HpuAB. Binding assays using [125I]-Hb revealed that the bipartite receptor has a single binding site for Hb (Kd 150 nM). Competitive binding assays using heterologous Hbs revealed that HpuAB Hb recognition was not species specific. The binding kinetics of Hb to HpuAB were dramatically altered in a TonB- mutant and in wild-type meningococci treated with the protonophore carbonylcyanide m-chlorophenylhydrazone (CCCP), indicating that TonB and an intact proton motive force are required for normal Hb binding and release from HpuAB. Our results support a model in which both HpuA and HpuB are required to form a receptor complex in the outer membrane with a single binding site, whose structure and ligand interactions are significantly affected by the TonB-mediated energy state of the receptor.

Bacterial Outer Membrane Proteins↗
PubMed2001

Mycobacterial growth in human macrophages: variation according to donor, inoculum and bacterial strain.

The microbicidal capacity of the macrophage is frequently evaded by mycobacteria, leading to tuberculosis (TB). We investigated a number of parameters affecting the rate of growth of mycobacteria in human monocyte-derived macrophages (MDM). The results show a great deal of variation in the growth of both Mycobacterium bovis BCG and M. tuberculosis H37Rv, using a large number of human macrophage donors, (132 and 40, respectively), but no correlation was seen with the TB status of the MDM donor. Clumping of the mycobacteria resulted in more vigorous growth in MDM, suggesting that inoculum size could affect disease progression. The growth rates of 17 clinical isolates of M. tuberculosis were measured in macrophages derived from three donors and no consistent or marked differences between isolates were observed over the 5-day period of growth measurement. However, all 17 clinical strains grew consistently faster than H37Rv in the same experiments.

Adolescent↗
PubMed2001

Lead toxicosis and trace element levels in wild birds and mammals at a firearms training facility.

In May 1999, lead poisoning was diagnosed in a yellow-rumped warbler (Dendroica coronata) and a gray squirrel (Sciurus carolinensis) found at the Federal Law Enforcement Training Center (FLETC), Glynn County, GA, based on detection of 6.2 and 90.0 ppm wet weight (WW) lead in the liver of the warbler and squirrel, respectively. From October 21--26, 1999, 72 wild animals (37 mammals and 35 birds), comprised of 22 different species, were collected from a 24-ha area surrounding the FLETC outdoor firearms shooting range complex to evaluate exposure to lead and other trace elements. Ten animals were used as controls (five mammals and five birds) and were collected from areas 1.5--3 km outside the shooting range area. Kidney and liver tissues were analyzed for lead, zinc, and other trace elements. Bird gizzards and white-tailed deer abomasums were examined grossly and radiographically to detect metallic objects. Twenty-four (33.3%) animals (11 species) had kidney or liver tissue lead levels > 1.00 ppm, and 12 of these (6 species) had levels > 2.00 ppm. Carcasses of one brown-thrasher (Toxostoma rufum) and two white-tailed deer (Odocoileus virginianus) contained lead fragments. Elevated liver tissue levels of zinc (111.0 ppm) were detected in one brown thrasher that also had elevated kidney and liver tissue lead levels. In February 2000, seven yellow-rumped warblers and one solitary vireo (Vireo solitarius) found dead near the FLETC firearms shooting range also were diagnosed with lead poisoning, with liver and kidney tissue lead levels from 1.77--11.6 and 4.55--17.8 ppm WW, respectively. This frequency of elevated tissue lead levels among the animals examined, in combination with confirmed lead toxicosis in both avian and mammalian species at FLETC, indicates significant lead exposure of local wild bird and mammal communities via bullets and fragments in and on the soil surface of the four outdoor ranges. Most FLETC firearms training is being shifted to new baffled ranges (four walls with semiopen top) with bullet recovery capabilities to preclude future deposition of lead in the environment; existing outdoor ranges will be remediated to remove existing lead.

Animals↗
PubMed2001

The basis of asymmetry in IS2 transposition.

In the first step of IS2 transposition, the formation of an IS2 minicircle, the roles of the two IS ends differ. Terminal cleavage initiates exclusively at the right inverted repeat (IRR) - the donor end - whereas IRL is always the target. At the resulting minicircle junction, the two abutted ends are separated by a spacer of 1 or 2 basepairs. In this study, we have identified the determinants of donor and target function. The inability of IRL to act as a donor results largely from two sequence differences between IRL and IRR - an extra basepair between the conserved transposase binding sequences and the end of the element, and a change of the terminal dinucleotide from CA-3' to TA-3'. These two changes also impose a characteristic size on the minicircle junction spacer. The only sequences required for the efficient target function of IRL appear to be contained within the segment from position 11-42. Although IRR can function as a target, its shorter length and additional contacts with transposase (positions 1-7) result in minicircles with longer, and inappropriate, spacers. We propose a model for the synaptic complex in which the terminus of IRL makes different contacts with the transposase for the initial and final strand transfer steps. The sequence differences between IRR and IRL, and the behavioural characteristics of IRL that result from them, have probably been selected because they optimize expression of transposase from the minicircle junction promoter, Pjunc.

DNA Transposable Elements↗
PubMed2001

Processes involved in the development of latent fingerprints using the cyanoacrylate fuming method.

Chemical processes involved in the development of latent fingerprints using the cyanoacrylate fuming method have been studied. Two major types of latent prints have been investigated-clean and oily prints. Scanning electron microscopy (SEM) has been used as a tool for determining the morphology of the polymer developed separately on clean and oily prints after cyanoacrylate fuming. A correlation between the chemical composition of an aged latent fingerprint, prior to development, and the quality of a developed fingerprint has been observed in the morphology. The moisture in the print prior to fuming has been found to be more important than the moisture in the air during fuming for the development of a useful latent print. In addition, the amount of time required to develop a high quality latent print has been found to be within 2 min. The cyanoacrylate polymerization process is extremely rapid. When heat is used to accelerate the fuming process, typically a period of 2 min is required to develop the print. The optimum development time depends upon the concentration of cyanoacrylate vapors within the enclosure.

Cyanoacrylates↗
PubMed2000

Galectin-1 induces partial TCR zeta-chain phosphorylation and antagonizes processive TCR signal transduction.

Galectin-1 is an endogenous lectin with known T cell immunoregulatory activity, though the molecular basis by which galectin-1 influences Ag specific T cell responses has not been elucidated. Here, we characterize the ability of galectin-1 to modulate TCR signals and responses by T cells with well defined hierarchies of threshold requirements for signaling distinct functional responses. We demonstrate that galectin-1 antagonizes TCR responses known to require costimulation and processive protein tyrosine phosphorylation, such as IL-2 production, but is permissive for TCR responses that only require partial TCR signals, such as IFN-gamma production, CD69 up-regulation, and apoptosis. Galectin-1 binding alone or together with Ag stimulation induces partial phosphorylation of TCR-zeta and the generation of inhibitory pp21zeta. Galectin-1 antagonizes Ag induced signals and TCR/costimulator dependent lipid raft clustering at the TCR contact site. We propose that galectin-1 functions as a T cell "counterstimulator" to limit required protein segregation and lipid raft reorganization at the TCR contact site and, thus, processive and sustained TCR signal transduction. These findings support the concept that TCR antagonism can arise from the generation of an inhibitory pp21zeta-based TCR signaling complex. Moreover, they demonstrate that TCR antagonism can result from T cell interactions with a ligand other than peptide/MHC.

Adjuvants, Immunologic↗
PubMed2000

Lead poisoning in a northern bobwhite in Georgia.

A northern bobwhite (Colinus virginianus) was observed with partial paralysis on 3 March 1997 and found dead on 8 March 1997 on Di-Lane Plantation Wildlife Management Area (Burke County, Georgia, USA). The juvenile male was necropsied by the Southeastern Cooperative Wildlife Disease Study (Athens, Georgia) and diagnosed with lead toxicosis. The bobwhite had liver tissue lead levels of 399 parts per million wet weight and two worn 1-mm diameter lead shot pellets were found in the gizzard.

Animals↗
PubMed1999

Galectin-1 specifically modulates TCR signals to enhance TCR apoptosis but inhibit IL-2 production and proliferation.

Galectin-1 is an endogenous lectin expressed by thymic and lymph node stromal cells at sites of Ag presentation and T cell death during normal development. It is known to have immunomodulatory activity in vivo and can induce apoptosis in thymocytes and activated T cells (1-3). Here we demonstrate that galectin-1 stimulation cooperates with TCR engagement to induce apoptosis, but antagonizes TCR-induced IL-2 production and proliferation in a murine T cell hybridoma and freshly isolated mouse thymocytes, respectively. Although CD4+ CD8+ double positive cells are the primary thymic subpopulation susceptible to galectin-1 treatment alone, concomitant CD3 engagement and galectin-1 stimulation broaden susceptible thymocyte subpopulations to include a subset of each CD4- CD8-, CD4+ CD8+, CD4- CD8+, and CD4+ CD8- subpopulations. Furthermore, CD3 engagement cooperates with suboptimal galectin-1 stimulation to enhance cell death in the CD4+ CD8+ subpopulation. Galectin-1 stimulation is shown to synergize with TCR engagement to dramatically and specifically enhance extracellular signal-regulated kinase-2 (ERK-2) activation, though it does not uniformly enhance TCR-induced tyrosine phosphorylation. Unlike TCR-induced IL-2 production, TCR/galectin-1-induced apoptosis is not modulated by the expression of kinase inactive or constitutively activated Lck. These data support a role for galectin-1 as a potent modulator of TCR signals and functions and indicate that individual TCR-induced signals can be independently modulated to specifically affect distinct TCR functions.

Adjuvants, Immunologic↗
PubMed1999

Phase variation of HpuAB and HmbR, two distinct haemoglobin receptors of Neisseria meningitidis DNM2.

We have previously described HpuAB, a two-component receptor that mediates binding to haemoglobin (Hb), haemoglobin-haptoglobin (Hb-Hp) and apo-haptoglobin (Hp). In this communication, we constructed non-polar mutations in the hpuA and hpuB loci to examine the individual roles of HpuA and HpuB. Our results indicate that both HpuA and HpuB are required for the acquisition of Fe from Hb and Hb-Hp. We isolated Hb utilization-positive (Hb+) variants of our Hb utilization-negative (Hb-) hpu mutants at a frequency of 10(-3) and demonstrated that the Hb+ phenotype resulted from the expression of a second Hb receptor, HmbR. Expression of HmbR in DNM2 was found to be controlled by translational frameshifting involving a polyguanine (G) tract located within the hmbR locus. The hpuA locus also contains a poly(G) tract, which suggested that meningococci could phase vary each Hb receptor independently by slip-strand mispairing in the poly(G) tracts found in hpuA and hmbR. Thus, we isolated a naturally occurring Hb- variant of DNM2, designated DNM2 Hb-, which did not express either HpuAB or HmbR. Hb+ variants of DNM2Hb- were selected and examined for HpuAB and HmbR expression. In each instance, acquisition of HpuAB or HmbR expression was correlated with phase variation in the poly(G) tract of each Hb receptor.

Bacterial Outer Membrane Proteins↗
PubMed1999

Mannose-binding protein B allele confers protection against tuberculous meningitis.

Inhalation is the principal mode of entry for Mycobacterium tuberculosis in humans. Primary infection is usually restricted to the lungs and contiguous lymph nodes. In a subset of infected individuals, predominantly children, the infection is spread hematogenously to the meninges. The host factors that influence the development of tuberculous meningitis have not been well elucidated. The mannose-binding protein (MBP), a serum protein, is considered as an "ante-antibody." MBP has been shown to bind mycobacteria and acts as an opsonin in vitro. Although MBP plays a role in first-line host defense, it may under certain circumstances be deleterious to the host. In tuberculosis (TB), MBP may assist the spread of this intracellular pathogen. Therefore, we hypothesized that MBP genotypes that result in a phenotype of low MBP levels might be protective. We studied a well-defined South African population in which TB has reached epidemic levels. We found that the MBP B allele (G54D), which disrupts the collagen region of the protein and results in low MBP levels, was found in 22 of 79 (28%) of the TB-negative controls from the same community, compared with 12 of 91 (13%) of the patients with pulmonary TB (p < 0.017), and 5 of 64 (8%) of patients with tuberculous meningitis (p < 0.002). In addition, we found significantly lower serum MBP concentrations in TB-negative controls compared with postacute phase, fully recovered TB patients (p < 0.004). These findings suggest that the MBP B allele affords protection against tuberculous meningitis.

Adult↗
PubMed1999

Potassium nitrite reaction with 11-nor-delta 9-tetrahydrocannabinol-9-carboxylic acid in urine in relation to the drug screening analysis.

Recently potassium nitrite has been used as an adulterant to interfere with the analysis of 11-nor-delta 9-tetrahydro-cannabinol-9-carboxylic acid (THC-COOH) in urine. A comprehensive study of the THC-COOH and nitrite reaction chemistry and stability under various conditions is presented. Reverse phase high performance liquid chromatography (HPLC) and negative electrospray mass spectrometry (ESMS) results are given to substantiate the derived reaction mechanism and properties leading to reaction termination. The addition of potassium carbonate as a buffering agent prior to or following sample void as a means of preventing the formation of a nitroso-complexed form of the 11-nor-delta 9+-tetrahydrocannabinol-9-carboxylic acid is evaluated.

Carbonates↗
PubMed1998

Transport of intact porphyrin by HpuAB, the hemoglobin-haptoglobin utilization system of Neisseria meningitidis.

The meningococcal hemA gene was cloned and used to construct a porphyrin biosynthesis mutant. An analysis of the hemA mutant indicated that meningococci can transport intact porphyrin from heme (Hm), hemoglobin (Hb), and Hb-haptoglobin (Hp). By constructing a HemA- HpuAB- double mutant, we demonstrated that HpuAB is required for the transport of porphyrin from Hb and Hb-Hp.

Aldehyde Oxidoreductases↗
PubMed1997

The Lck SH2 phosphotyrosine binding site is critical for efficient TCR-induced processive tyrosine phosphorylation of the zeta-chain and IL-2 production.

The lymphocyte-specific tyrosine kinase Lck is essential for TCR-mediated signal transduction. This is in part due to its enzymatic activity as a tyrosine kinase responsible for TCR-induced tyrosine phosphorylation of zeta and CD3 receptor subunits. In addition to its catalytic domain, the Lck protein contains SH3 and SH2 domains capable of associating with other signaling molecules. It has been proposed that phosphotyrosine binding by the Lck SH2 domain may enhance substrate tyrosine phosphorylation by facilitating the processive phosphorylation of multiple sites within the TCR complex. Alternatively or additionally, it may function in adapter activity for facilitating required protein-protein interactions. Previous experiments demonstrate that overexpression of a constitutively activated form of Lck (F505) in the BI-141 T cell hybridoma leads to the Lck kinase activity-dependent enhancement of TCR-mediated signals. Here we demonstrate that mutation of amino acids important for SH2 phosphotyrosine binding significantly compromises the ability of F505 to enhance TCR-mediated protein tyrosine phosphorylation and Ag-induced IL-2 production in BI-141. Examination of the effects of TCR-regulated phosphorylation of the Lck substrate zeta provides in vivo evidence for a role for the Lck SH2 domain in the processive phosphorylation of a multiply phosphorylated substrate.

Binding Sites↗
PubMed1997

T cell antigen receptor-induced IL-2 production and apoptosis have different requirements for Lck activities.

The T cell hybridoma BI-141 has been previously used to dissect the roles of Lck in Ag-induced IL-2 production. Here we demonstrate that BI-141 undergoes apoptosis in response to TCR stimulation using Ag or anti-TCR Abs. Using a panel of BI-141 transfectants expressing constitutively activated Lck (F505) or phosphotyrosine-binding (K154F505 and C156F505) or kinase-impaired (R273F505) mutants, we assess the relative requirements for Lck in TCR-mediated IL-2 production and apoptosis. While BI-141 transfectants expressing F505 are dramatically enhanced in their ability to produce IL-2 in response to Ag relative to K154F505-, C156F505-, or R273F505-expressing transfectants, no differences between these transfectants are observed in their ability to undergo TCR-induced apoptosis. TCR-induced Fas ligand (FasL) expression is demonstrated to be dependent on Lck SH2 and kinase activities, although FasL expression cannot be correlated with apoptosis. Low levels of Fas are constitutively expressed at equal levels on transfectants and are not increased in response to TCR ligation. Together, these data indicate that TCR-induced apoptosis in BI-141 is regulated through a mechanism(s) distinct from the Lck-induced expression of Fas, FasL, or IL-2 production. This TCR signal may be independent of Lck kinase and SH2 activities, or may require lower threshold activity. The identification of differential requirements for particular T cell functions is crucial to understanding how TCR engagement affects downstream T cell functions and may aid in the rational design of therapeutics aimed at specifically modulating particular T cell responses.

Animals↗
PubMed1997

Phylogenetic relationships of the liverworts (Hepaticae), a basal embryophyte lineage, inferred from nucleotide sequence data of the chloroplast gene rbcL.

Sequence data from the chloroplast-encoded gene rbcL were obtained for 24 liverworts, a basal group of embryophytes. Maximum likelihood and parsimony analyses of these data, along with data from other major green plant lineages, confirm hypotheses based on morphological data, such as the paraphyly of bryophytes, and the basal position of liverworts. Molecular data corroborate the deep separation between the complex thalloid and leafy/simple thalloid liverworts implied by morphological data, but the monophyly of liverworts could not be rejected. The effects of accounting for site-to-site rate heterogeneity in these data were examined using maximum likelihood methods. Comparison of trees obtained with and without rate heterogeneity showed that simply allowing for heterogeneity had a greater improvement on likelihood score than optimization of transition/transversion bias. Incorporation of site-to-site rate heterogeneity in the larger analysis, however, did not necessarily change which topology was favored. Properties of rbcL sequences from the two liverwort groups were compared. Significantly different substitution rates were found between leafy/simple thalloid and complex thalloid liverwort taxa, with rates of rbcL sequence evolution in leafy/simple thalloid taxa being higher and more indicative of those of vascular plants, and with those of complex thalloid taxa (such as Marchantia) being slower. Codon usage in rbcL in complex thalloid liverworts was biased toward NNU and NNA, compared to the leafy/simple thalloid liverworts. Although base composition and relative substitution rates differed between the two groups, no significant differences were detected within each of the two groups of liverworts. The signal present in first and second codon sites versus third codon sites was compared. While the third codon positions in rbcL across this taxon sampling are highly variable (with only 15 constant sites of 439), the trees obtained were in general agreement with trees from the entire data set and with trees obtained from independent sources of data. The presence of signal in third codon positions across greater than 400 MY of plant evolution means that definitions of saturation based on pair-wise comparisons of sequences inadequately assess phylogenetic signal.

Chloroplasts↗