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D H Walker

Publications and source records attributed to D H Walker.

At least 127 records · Page 7Linked to original sources
PubMed1992

Antigenic characterization of ehrlichiae: protein immunoblotting of Ehrlichia canis, Ehrlichia sennetsu, and Ehrlichia risticii.

In recent years a febrile illness apparently associated with tick bite in patients in the United States has been attributed to infection by an Ehrlichia species. This implication is based on serologic responses to E. canis, morphologic demonstration of ehrlichiae in clinical materials, and a single isolate distinct from E. canis which was obtained from a human patient by the Centers for Disease Control. Little is known about the antigens of the ehrlichiae. This report expands the breadth of available knowledge concerning the antigenic components and serologic responses to component antigens of E. canis, E. sennetsu, and E. risticii. Protein immunoblotting after sodium dodecyl sulfate-polyacrylamide gel electrophoresis by using density gradient-purified ehrlichiae and homologous antisera demonstrated reproducible and characteristic antigens within each species (for E. sennetsu, 91, 64, 54, 44, 36, 34, 28, 25, and 24 kDa; for E. risticii, 70, 52, 48, 44, 35, 28, 24, 23, and 20 kDa; for E. canis, 110, 64, 52, 42, 33, 28, 24, 23, and 20 kDa). When antisera were reacted with heterologous antigens, cross-reactivity among these species was virtually restricted to the 70-kDa antigen. Furthermore, when serum samples obtained from 10 patients who were convalescing from ehrlichiosis were tested against each antigen, only three serum samples had any reactivities, and these serum samples reacted with only a few of the antigenic bands. These results documented the molecular sizes of electrophoretically separated antigens of the three Ehrlichia species, confirm their serologic relationships, and support the novel nature of the agent(s) of human ehrlichiosis in the United States.

Animals↗
PubMed1992

Antigenic diversity of Rickettsia conorii.

Analysis of seven strains designated as Rickettsia conorii for reactivity with a panel of 12 monoclonal antibodies to surface-protein epitopes of spotted fever group rickettsiae and by Western immunoblotting with standard serotyping sera revealed remarkable antigenic diversity. Rickettsial strains from France, Morocco, Ethiopia, Kenya, South Africa, India, and the USSR differed from one another in reactivity with at least one and as many as five monoclonal antibodies. Simko and Indian strains were similar to one another and differed substantially from other R. conorii strains. All seven strains reacted with three R. conorii-specific monoclonal antibodies. Western immunoblotting demonstrated a major 120-kD protein and a major 135-kD protein in all strains. The principal differences were the presence of a major undenatured 130-kD protein in all strains except Indian and Simko, which had an analogous protein of 124 kD. Immunodominant antigenically related, heat-denatured protein bands of 170 kD (Malish 7 strain), 175 kD (Manuel strain), and 190 kD (Kenya tick typhus, Indian, and Simko strains) were not detected in the M-1 and Moroccan strains. This antigenic diversity is greater than that previously reported for other spotted fever group rickettsial species, suggesting that R. conorrii is an older species than R. rickettsii with a longer period of time for evolutionary divergence.

Animals↗
PubMed1991

Role for cyclin A in the dependence of mitosis on completion of DNA replication.

THE cyclins were first identified by their cell-cycle-dependent synthesis and destruction and have a key role in the control of mitosis in Xenopus embryonic cell cycles. All higher eukaryotes have at least two types of cyclins, the A- and B-type, which can be distinguished by sequence motifs and the timing of their destruction in the cell cycle. The degradation of both cyclins is required for exit from mitosis, but the activation and destruction of cyclin A occur earlier in the cell cycle than with the B-type cyclins. This suggests that cyclin A has a distinct role in cell-cycle progression. We have used an antisense oligodeoxy-nucleotide directed against cyclin A to investigate this role. Ablation of cyclin A messenger RNA in cytostatic factor/metaphase-arrested extracts of Xenopus eggs, followed by in vitro progression into interphase, resulted in the premature appearance of cyclin B-cdc2-associated H1 kinase activity and premature entry into mitosis. Although cyclin A-ablated extracts could initiate DNA synthesis during interphase, S phase was not completed before entry into mitosis. The effects of cyclin A ablation were reversed by the addition of cyclin A mRNA or cyclin A protein to the extracts.

Animals↗
PubMed1991

Clinical and laboratory features of murine typhus in south Texas, 1980 through 1987.

OBJECTIVE: --The clinical and laboratory features of patients with murine typhus have not been extensively reviewed since 1946. We have updated these findings in patients from south Texas who were examined by modern clinical and laboratory methods from 1980 through 1987. DESIGN: --Patients were identified by serological methods in this case series, and clinical, epidemiologic, laboratory, and therapeutic data were compiled and analyzed. SETTING: --The majority of patients (77 of 80) were identified in a primary care community hospital setting; the remainder (3 of 80) were ambulatory hospital outpatients. PATIENTS: --From 1980 through 1987, a total of 345 patients were diagnosed with murine typhus; 90 of these patients were seen at four hospitals in south Texas; of these, 80 had clinical and laboratory data available for review. MAIN OUTCOME MEASURES: --The frequency of common clinical manifestations (eg, headache, fever, and rash) and laboratory findings (eg, leukocyte and platelet counts and serum chemistry abnormalities) of patients with infectious diseases was tabulated. Clinical severity was semiquantitatively assessed and was correlated with clinical, laboratory, and therapeutic results. RESULTS: --Most cases (69%) occurred from April through August. Rash occurred in 54%; the triad of fever, headache, and rash was observed in only 12.5% of patients when first examined by a physician; respiratory and gastrointestinal symptoms were also frequent. Multiple organ involvement was documented by frequent abnormal laboratory findings of the hematologic, respiratory, hepatic, and renal systems. Disease severity was related to older patient age, the presence of renal dysfunction, leukocytosis, and hypoalbuminemia, and previous therapy with sulfa antibiotics. CONCLUSIONS: --Infection by Rickettsia typhi causes a systemic illness with clinical and laboratory abnormalities not previously recognized or described. Early clinical diagnosis and treatment are needed to avoid undue morbidity and mortality.

Diagnosis, Differential↗
PubMed1991

Ehrlichia.

Explore the source record for details and available documents.

Animals↗
PubMed1991

Epidemiology of rickettsial diseases.

Rickettsial diseases have a diversity of epidemiologic characteristics reflective of the variety of ecologic situations in which the obligate intracellular bacteria are transmitted to humans. For the spotted fever group (SFG) rickettsiae, Rickettsia typhi, R. tsutsugamushi, Coxiella burnetii, and the human ehrlichial agent, humans are a dead-end host who plays no role in the maintenance of the organism in nature. All rickettsioses exist as zoonoses. Moreover, all rickettsiae are found in infected arthopods, which generally serve as the natural hosts and can transmit the infection to the next generation of ticks, mites, chiggers, or fleas. From our anthropocentric viewpoint, Q fever aerosol infection from parturient animals and Brill-Zinsser disease ignited epidemics of louse-borne epidemic typhus are exceptions. However, silent cycles of C. burnetii in ticks and R. prowazekii in the flying squirrel flea may have maintained these agents in transovarial or enzootic cycles for eons before humans and their domestic animals arrived on the scene. Thus, the epidemiology of rickettsial diseases must be recognized as an unfortunate aberration of the rickettsial economy. Several excellent reviews of rickettsial ecology contain a wealth of useful information.

Animals↗
PubMed1991

Activation of p34cdc2 kinase by cyclin A.

Functional clam cyclin A and B proteins have been produced using a baculovirus expression system. Both cyclin A and B can induce meiosis I and meiosis II in Xenopus in the absence of protein synthesis. Half-maximal induction occurs at 50 nM for cyclin A and 250 nM for cyclin B. Addition of 25 nM cyclin A to activated Xenopus egg extracts arrested in the cell cycle by treatment with RNase or emetine activates cdc2 kinase to the normal metaphase level and stimulates one oscillatory cell cycle. High levels of cyclin A cause marked hyperactivation of cdc2 kinase and a stable arrest at the metaphase point in the cell cycle. Kinetic studies demonstrate the concentration of cyclin A added does not affect the 10 min lag period required for kinase activation or the timing of maximal activity, but does control the rate of deactivation of cdc2 kinase during exit from mitosis. In addition, exogenous clam cyclin A inhibits the degradation of both A- and B-type endogenous Xenopus cyclins. These results define a system for investigating the biochemistry and regulation of cdc2 kinase activation by cyclin A.

Animals↗
PubMed1991

Rocky Mountain spotted fever.

Rocky Mountain spotted fever, the most prevalent rickettsial disease in the United States, is one of the most severe of all infectious diseases. It remains an important infectious disease because of its prevalence, the difficulty of clinical diagnosis, potentially fatal outcome, and lack of a widely available sensitive and specific diagnostic test during the acute stage of the illness.

Animals↗
PubMed1990

Stimulation of purified phosphatidylinositol 4-kinase by cobra venom cardiotoxin.

Cobra venom cardiotoxin was found to stimulate the phosphatidylinositol kinase activity present in A431 cell membranes and in detergent extracts of these membranes. Incubation of highly purified phosphatidylinositol 4-kinase from this source with cardiotoxin resulted in a 2- to 3-fold stimulation of phosphatidylinositol kinase activity. The activation of the purified phosphatidylinositol 4-kinase by cardiotoxin was time- and dose-dependent and appeared to be associated with a decrease in the Km apparent of the enzyme for phosphatidylinositol with no change in the Vmax apparent of the enzyme. The data suggest that the phosphatidylinositol 4-kinase is activated by direct interaction of the enzyme with cobra venom cardiotoxin.

1-Phosphatidylinositol 4-Kinase↗
PubMed1990

Biological characterization of major polypeptides on the surface of spotted fever group rickettsiae.

There are two major polypeptides on the surface of spotted fever group rickettsiae that play important roles as immunogens and possibly relate to the pathogenicity of rickettsial diseases. Digestion with trypsin and staphylococcal V-8 protease shows that the 115-kDa protein of Rickettsia conorii is a trypsin-sensitive, surface-exposed protein. The 135-kDa protein is relatively trypsin resistant. Both proteins resist heat treatment up to 52 degrees C and maintain their antigenic reactivity with monoclonal antibodies when the intact rickettsiae are heated. When rickettsiae are dissolved in SDS-containing sample buffer, these polypeptides lose their antigenic reactivity with monoclonal antibodies after incubation at 45 degrees C for 10 min. Staphylococcal V-8 protease does not appear to affect these polypeptides under the current experimental conditions. Monoclonal antibody to the 115-kDa protein reduces rickettsial attachment. The 115-kDa polypeptide may play a role in rickettsial adhesion to the host cell surface.

Bacterial Adhesion↗
PubMed1990

Species-specific monoclonal antibodies to Rickettsia japonica, a newly identified spotted fever group rickettsia.

A total of 192 hybridomas were developed from mice immunized with Rickettsia japonica, a newly identified spotted fever group rickettsia pathogenic for humans. Of these hybridomas, 101 were species specific, 37 were spotted fever group reactive, and the other 54 were also reactive with one or more of the other pathogenic species of spotted fever group rickettsiae, Rickettsia akari, Rickettsia australis, Rickettsia conorii, Rickettsia rickettsii, and Rickettsia sibrica. Seven of the species-specific monoclonal antibodies were characterized. These monoclonal antibodies all belong to the immunoglobulin G class and react with all five strains of R. japonica at the same immunofluorescence titers, indicating that the five strains all belong to a single species. The species-specific epitopes reactive with these monoclonal antibodies are located on the surface proteins of the organisms demonstrated as 145- and 120-kilodalton bands on Western immunoblots. These two antigenic bands were shown to be proteins, because treatment with proteinase K completely destroyed the reactivity of the bands with the monoclonal antibodies.

Animals↗
PubMed1990

Vascular permeability and coagulation during Rickettsia rickettsii infection in dogs.

The vascular permeability of the ocular fundus, alterations in the coagulation system, and plasma concentrations of thromboxane B2 (TXB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) were studied in dogs following intradermal inoculation with 5 x 10(5) TCID50 of Rickettsia rickettsii. Twenty-four to 48 hours after the onset of fever and rickettsemia, multifocal areas of retinal vasculitis were evident, which corresponded to areas of altered vascular permeability demonstrated by fluorescein angiography. The number and intensity of retinal vessels with sodium fluorescein leakage peaked during the second week after inoculation, and retinal vascular permeability remained altered during the third week of infection, well past the phase of clinical and clinicopathologic recovery. Development of retinal vasculitic foci was associated with thrombocytopenia, increased concentrations of circulating fibrinogen, and slight prolongation of activated partial thromboplastin time. Increased concentrations of fibrin/fibrinogen degradation products were detected in 4 of 9 dogs. Despite the degree of vascular endothelial damage evident on fluorescein angiographic and histologic studies in these dogs, plasma TXB2 and 6-keto-PGF1 alpha concentrations were not increased.

6-Ketoprostaglandin F1 alpha↗