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Biomedical subjects

P Ames

Publications and source records attributed to P Ames.

13 recordsLinked to original sources
PubMed1997

Fetal proteins and chronic treatment with low-dose erythropoietin.

The potential stimulating effect of erythropoietin on the production of fetal proteins (FPs) has not been explored in human subjects. Therefore, the plasma levels of fetal fibrinogen (FF), carcinoembriogenic antigen (CEA), alpha-fetoprotein (AFP), and fetal hemoglobin (HbF) were measured in 12 uremic hemodialyzed patients before the first administration and after 1, 2, and 3 months of low-dose erythropoietin (r-Hu-EPO; 45 U/kg body wt I.V., thrice weekly). Such a treatment efficaciously increased total hemoglobin (Hb). CEA and AFP increased from 5.8 +/- 1.1 ng/ml and 2.9 +/- 0.9 ng/ml to the final value of 43.2 +/- 3.9 ng/ml and 8.7 +/- 1.1 ng/ml, respectively, in the absence of detectable neoplastic diseases. The levels of FF did not change. HbF levels increased from <3% of Hb to the peak value of 48% at the end of the first month; subsequently, a progressive reduction in HbF was observed. Similar changes were detected in the reticulocyte count (RET). A striking correlation was found between HbF and RET (r = 0.8633, p < 0.0001), indicating that the increment in HbF was dependent on the erythroid activity. In conclusion, this study evidences broader than expected effects of erythropoietin on the synthesis of FP and suggests that (1) r-Hu-EPO markedly increases HbF in a condition of suppressed bone marrow activity, (2) the measurement of the cell proliferation markers CEA and AFP is unreliable during r-Hu-EPO therapy, and (3) the prothrombotic state associated with chronic r-Hu-EPO treatment in patients with uremia cannot be attributed to the presence of FF.

Adult↗
PubMed1996

Transformation in recurrent ovarian granulosa cell tumors: Ki67 (MIB-1) and p53 immunohistochemistry demonstrates a possible molecular basis for the poor histopathologic prediction of clinical behavior.

Ovarian granulosa cell tumors (GCTs) behave unpredictably. Stage I patients suffer recurrences many years after treatment, and histopathologic evaluation of the primary GCT offers only a few clues. Grading, in particular, is largely ineffective. Ki67 (MIB-1) and p53 monoclonal antibodies (active on paraffin embedded tissues) provide insight into nuclear proliferation and control, respectively. In this study, the authors hypothesized that these molecular markers will help predict the clinical behavior of GCTs. Paraffin sections from 68 GCTs (arising in 56 patients: 53 primary and 15 recurrent) including 34 typical and 27 diffuse adult, and seven juvenile types were immunostained for Ki67 (MIB-1 clone; Immunotech, Westbrook, ME) and p53 (DO7 clone; Novacastra Laboratories, UK). The Ki67 proliferation index (Ki67PI = percentage immunoreactive on a count of at least 400 nuclei) ranges from 1 to 50% (mean, = 12.2%; median, 9.3%). Nineteen percent of GCTs exhibited focal p53 immunoreactivity; the number of GCTs and proportion of nuclei decorated were as follows: four, <1%; seven, 1% to 10%; and one, 20%. Ki67PI was higher in recurrent tumors (P<.001) and correlated with mitotic rate (r = .75; P<.0001). p53 staining was associated with juvenile type GCTs (P<.001) and higher Ki67PI (P<.005). Other histopathologic features exhibited no association with p53 staining or Ki67PI. Follow-up was available for 54 of 56 patients: 18 suffered recurrences after 16 to 229 months (mean, 72.1 months; median 59 months), and 36 were disease free 16 to 369 months (mean, 78.2 months; median, 70 months) after diagnosis. Curiously, high Ki67PI and mitotic rates of primary GCT correlated weakly with a disease-free course (P=.03 and .07 respectively). Disease recurrence was associated with stage >I (P<.0005), vessel invasion in the capsule (P<.001), ruptured tumors (P<.005), and older patients (P<.02). p53 staining and size or subtype of GCT exhibited no prognostic value. For 12 patients, paired primary and first recurrence of GCT showed a striking increase in Ki67PI (P<.00005) and mitotic activity (P<.02) in the recurrence. p53 expression also appeared (de novo) in two recurrent GCTs. The interpretation of focal p53 staining (>10% nuclei decorated in only one GCT) is controversial. Some investigators suggest that this represents overexpression of wild type p53 rather than p53 gene mutation. Primary GCTs exhibit a wide spectrum of proliferative activity, and the seven juvenile GCTs (the most proliferative type) demonstrated no recurrences in this study. Recurrent GCTs displayed a transformation of molecular markers to increased proliferative activity and overexpression of p53, fundamentally, by these markers, a different GCT than the primary one. These findings suggest a molecular basis for the lack of histopathologic predictors for recurrence. Factors other than proliferation of the primary GCT (which relates most closely to grading) either extrinsic to the neoplasm (host dependent) or as yet undetectable must determine malignant behavior.

Adolescent↗
PubMed1996

Methylation segments are not required for chemotactic signalling by cytoplasmic fragments of Tsr, the methyl-accepting serine chemoreceptor of Escherichia coli.

The serine chemoreceptor Tsr and other methyl-accepting chemotaxis proteins (MCPs) control the swimming behaviour of Escherichia coli by generating signals that influence the direction of flagellar rotation. MCPs produce clockwise (CW) signals by stimulating the autophosphorylation activity of CheA, a cytoplasmic histidine kinase, and counter-clockwise signals by inhibiting CheA. CheW couples CheA to chemoreceptor control by promoting formation of MCP/CheW/CheA ternary complexes. To identify MCP structural determinants essential for CheA stimulation, we inserted fragments of the tsr coding region into an inducible expression vector and used a swimming contest called 'pseudotaxis' to select for transformant cells carrying CW-signalling plasmids. The shortest active fragment we found, Tsr (350-470), stimulated CheA in a CheW-dependent manner, as full-length Tsr molecules do. It spans a highly conserved 'core' (370-420) that probably specifies the CheA and CheW contact sites and other determinants needed for stimulatory control of CheA. Tsr (350-470) also carries portions of the left and right arms flanking the core, which probably play roles in regulating MCP signalling state. However, this Tsr fragment lacks all of the methylation sites characteristic of MCP molecules, indicating that methylation segments are not essential for generating receptor output signals.

Amino Acid Sequence↗
PubMed1994

Constitutively signaling fragments of Tsr, the Escherichia coli serine chemoreceptor.

Tsr, the serine chemoreceptor of Escherichia coli, has two signaling modes. One augments clockwise (CW) flagellar rotation, and the other augments counterclockwise (CCW) rotation. To identify the portion of the Tsr molecule responsible for these activities, we isolated soluble fragments of the Tsr cytoplasmic domain that could alter the flagellar rotation patterns of unstimulated wild-type cells. Residues 290 to 470 from wild-type Tsr generated a CW signal, whereas the same fragment with a single amino acid replacement (alanine 413 to valine) produced a CCW signal. The soluble components of the chemotaxis phosphorelay system needed for expression of these Tsr fragment signals were identified by epistasis analysis. Like full-length receptors, the fragments appeared to generate signals through interactions with the CheA autokinase and the CheW coupling factor. CheA was required for both signaling activities, whereas CheW was needed only for CW signaling. Purified Tsr fragments were also examined for effects on CheA autophosphorylation activity in vitro. Consistent with the in vivo findings, the CW fragment stimulated CheA, whereas the CCW fragment inhibited CheA. CheW was required for stimulation but not for inhibition. These findings demonstrate that a 180-residue segment of the Tsr cytoplasmic domain can produce two active signals. The CCW signal involves a direct contact between the receptor and the CheA kinase, whereas the CW signal requires participation of CheW as well. The correlation between the in vitro effects of Tsr signaling fragments on CheA activity and their in vivo behavioral effects lends convincing support to the phosphorelay model of chemotactic signaling.

Bacterial Proteins↗
PubMed1988

Transmembrane signaling by bacterial chemoreceptors: E. coli transducers with locked signal output.

Methyl-accepting chemotaxis proteins (MCPs) function as transmembrane signalers in bacteria. We isolated and characterized mutants of the E. coli Tsr protein that produce output signals in the absence of overt stimuli and that are refractory to sensory adaptation. The properties of these "locked" transducers indicate that MCP molecules are capable of generating signals that actively augment clockwise and counter-clockwise rotation of the flagellar motors. Transitions between MCP signaling states can be influenced by amino acid replacements in many parts of the molecule, including the methylation sites, at least one of the two membrane-spanning segments, and a linker region connecting the receptor and signaling domains. These findings suggest that transmembrane signaling may involve direct propagation of conformational changes between the periplasmic and cytoplasmic portions of the MCP molecule.

Amino Acid Sequence↗
PubMed1987

Opsonophagocytic killing antibody to Pseudomonas aeruginosa mucoid exopolysaccharide in older noncolonized patients with cystic fibrosis.

The principal cause of morbidity and mortality in cystic fibrosis is persistent respiratory colonization with mucoid strains of Pseudomonas aeruginosa. To investigate possible mechanisms of resistance to this organism, we studied serum from 16 older (greater than or equal to 12 years) patients not colonized with mucoid P. aeruginosa, 11 older (greater than or equal to 14 years) colonized patients, 10 younger (less than or equal to 11 years) noncolonized patients, and 20 healthy adults. The samples from the older patients not colonized with mucoid P. aeruginosa contained antibody specific to the mucoid-exopolysaccharide antigen, which could mediate bacterial killing in conjunction with complement and white cells (titers of 4 to 80). These opsonophagocytic killing antibodies were not detected in samples from the 20 normal controls (P less than 0.0001 vs. noncolonized older patients) or 9 of 10 younger (less than or equal to 11 years) noncolonized patients (P = 0.0072 vs. noncolonized older patients). Although the patients with chronic colonization had higher titers of serum opsonophagocytic killing antibody than did the older noncolonized patients (P = 0.0005), these antibodies were not specific to the mucoid-exopolysaccharide antigen. We conclude that there is an association between mucoid-exopolysaccharide-specific opsonophagocytic killing antibody and a lack of detectable P. aeruginosa colonization in a subset of older, relatively healthy patients with cystic fibrosis.

Adolescent↗
PubMed1985

Opsonophagocytic killing activity of rabbit antibody to Pseudomonas aeruginosa mucoid exopolysaccharide.

We used an in vitro opsonophagocytic killing assay to measure the functional activity of antibody directed at the mucoid exopolysaccharide (MEP) antigen expressed by Pseudomonas aeruginosa strains isolated from cystic fibrosis patients. Rabbit antibodies raised to purified MEP were able to mediate phagocytic killing in the presence of human peripheral blood leukocytes and a low level (final concentration, 0.3%) of fresh normal human serum as a complement source. No bacterial killing was observed when peripheral blood leukocytes, antiserum, or complement was omitted. Specificity of the antibody for the MEP antigen was shown by adsorption and inhibition assays. Affinity-purified antibody to MEP also mediate phagocytic killing. These data indicate that antiphagocytic properties attributable to MEP can be overcome by specific antibody.

Animals↗
PubMed1984

Mediation of the killing of rough, mucoid isolates of Pseudomonas aeruginosa from patients with cystic fibrosis by the alternative pathway of complement.

The mechanism of killing of 12 serum-sensitive strains of mucoid Pseudomonas aeruginosa isolated from patients with cystic fibrosis was investigated. A quantitative assay indicated that more than 90% of cells were killed in 50% normal human serum (NHS). All strains failed to grow in NHS concentrations of greater than 10%. Killing was unaffected by adsorption of NHS with the mucoid bacteria or chelation with MgCl2-ethyleneglycol bis(beta-aminoethyl ether)N,N1-tetraacetate (MgCl2-EGTA) but was abolished in serum heated to 50 C for 20 min. Incubation of NHS with mucoid P. aeruginosa reduced the hemolytic capability of MgCl2-EGTA-chelated NHS against rabbit red blood cells by 56%-99%. Killing of the serum-sensitive mucoid strains was also seen in hypogammaglobulinemic serum. These data suggest that killing of such strains by NHS can occur via antibody-independent activation of the alternative pathway of complement. The importance of this finding lies in the implication that complement levels in the lungs of patients with cystic fibrosis who are colonized by these organisms are inadequate to deal with this chronic, progressive infection.

Adult↗
PubMed1984

Rhizobia are attracted to localized sites on legume roots.

Clouds of Rhizobium meliloti were attracted to localized sites on the surface of the infectible region of alfalfa roots. This behavior, which required active motility and chemotaxis, was not species specific. Correlation between the behavior of various mutants and their competitiveness for nodulation suggests that cloud formation has a role in the infection of host legume roots by rhizobia.

Chemotaxis↗
PubMed1981

Competitive advantage provided by bacterial motility in the formation of nodules by Rhizobium meliloti.

The effect of motility on the competitive success of Rhizobium meliloti in nodule production was investigated. A motile strain formed more nodules than expected when mixed at various unfavorable ratios with either flagellated or nonflagellated nonmotile derivatives. We conclude that motility confers a selective advantage on rhizobia when competing with nonmotile strains.

Medicago sativa↗
PubMed1980

Behavioral mutants of Rhizobium meliloti.

Rhizobium meliloti exhibited behavior resembling that of other chemotactic bacteria. Nonflagellated, nonmotile but flagellated, and nonchemotactic mutants were isolated, and genetic mapping placed all three types of lesions within a small region of the R. Meliloti chromosome. Results from nodulation experiments performed with these mutants indicate that members of the three classes (Fla-, Mot-, and Che-) infect and produce as many nodules on alfalfa plants as does the wild-type strain.

Chemotaxis↗
PubMed1979

The influence of chemotherapy on response of patients with hematologic malignancies to influenza vaccine.

Bivalent influenza vaccine (containing antigens A/Victoria and A/New Jersey) was administered to 52 patients with hematologic malignancies, and pre- and postvaccination antibody titers to both antigens were determined by hemagglutination-inhibition. In comparison to healthy controls, mean antibody titer elevations were lower for both antigens in all disease groups, being significant (p less than 0.05) for A/Victoria in patients with non-Hodgkin's lymphoma, acute leukemia and lymphoproliferative diseases, and for A/New Jersey in patients with Hodgkin's and non-Hodgkin's lymphomas. In comparison to controls, significant depression of antibody response to both antigens was seen in patients on combination chemotherapy (p less than 0.0005), to a lesser extent in patients on daily single alkylating agent chemotherapy (p less than 0.05), while untreated patients did not differ significantly. Lymphopenia and depressed immunoglobulin levels were associated with a higher failure rate in eliciting "protective" greater than or equal to fourfold antibody titer increases. The findings suggest that patients with hematologic malignancies who are receiving chemotherapy at the time of vaccination are unlikely to attain seroconversion to protective antibody levels with influenza vaccine.

Antibodies, Viral↗