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Biomedical subjects

D H Walker

Publications and source records attributed to D H Walker.

At least 145 records · Page 8Linked to original sources
PubMed1990

Kinetics of IgM and IgG responses to experimental and naturally acquired Rickettsia rickettsii infection in dogs.

The kinetics of specific IgM and IgG antibody response was characterized in four 9-month-old Beagles after inoculation of 2 x 10(2) plaque-forming units (PFU) of Sheila Smith strain of Rickettsia rickettsii. Immunoglobulin M antibodies were first detected by indirect immunofluorescence on postinoculation (PI) day 9, peaked by PI day 20, and were no longer detectable by PI day 80. Immunoglobulin G antibodies became detectable between PI days 22 and 28, peaked by PI day 42, and decreased gradually through PI day 130. Subsequent challenges with R rickettsii on PI days 216 (2 x 10(2) PFU/dog) and 1,029 (5 x 10(4) tissue culture infective dose [TCID50]/dog) resulted in slightly different serologic responses. The initial challenge exposure failed to increase the concentration of IgG antibodies and induced only low concentrations of IgM antibodies. After the second challenge inoculation, IgM antibodies were not detectable and the concentration IgG antibodies increased slightly. Clinical abnormalities and seroconversion were documented in control dogs following each challenge exposure. Examination of acute and convalescent serum samples from 55 dogs in which Rocky Mountain spotted fever was suspected clinically suggested that sole evaluation of IgM antibodies in acute-phase serum would result in inaccurate diagnoses because of false-positive and -negative results. Use of a composite conjugate that detects IgM and IgG antibodies to R rickettsii appears to be satisfactory for diagnostic purposes; however, concurrent quantitation of IgM antibodies may facilitate serodiagnosis in a select group of dogs in which a four-fold increase in convalescent antibody titer is not detected by use of the composite conjugate.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Mechanism of upper gastrointestinal hemorrhage in Mediterranean spotted fever.

Gastrointestinal (GI) hemorrhage is not a common complication of Mediterranean spotted fever (MSF). We describe three MSF cases with upper digestive tract bleeding in patients from Salamanca (Spain) and the results of the histologic studies performed in two of them. Besides the classical clinical triad of the disease (fever, rash and lesion at the site of tick bite, 'tache noire'), these patients presented purpuric rash and hypoalbuminemia, previously identified in severe forms of the disease. The hemorrhagic complication occurred late in the course of the MSF (between 13 and 20 days after the onset of fever) and was the consequence of multiple acute superficial erosions of the gastric mucosa. The histologic substrate of these lesions was identified as a vasculitic process - characteristically lymphohistiocytic - affecting the small vessels of the gastric wall. Rickettsial vascular injury at this level of the digestive tract is histologically similar to that observed in other organs in patients with MSF and may manifest clinically as digestive tract bleeding.

Aged↗
PubMed1989

Histopathology and immunohistologic demonstration of the distribution of Rickettsia typhi in fatal murine typhus.

An 81-year-old woman had chills, fever, nausea, vomiting, and epigastric pain. On day 3 she had hematuria and was treated with trimethoprim-sulfamethoxazole. On day 5 she had a cough, hypotension, anemia, azotemia, and elevated hepatic enzyme levels. Her condition deteriorated with thrombocytopenia, anuria requiring dialysis, edema, and hypoalbuminemia. Treatment with chloramphenicol and doxycycline was started on day 10. By day 11, she was in hypotensive shock; on day 12 she had seizures and died. Murine typhus was diagnosed by demonstration of antibodies to Rickettsia typhi by indirect immunofluorescence. Necropsy revealed interstitial pneumonia, pulmonary edema, hyaline membranes, alveolar hemorrhages, petechiae and vasculitis in the central nervous system, interstitial myocarditis, multifocal interstitial nephritis and hemorrhages, splenomegaly, portal triaditis, and mucosal hemorrhages in urinary tract. Immunofluorescent R. typhi were demonstrated in the lungs, brain, kidneys, liver, and heart. This unusual death occurred in an elderly patient without rash who was treated too late with antirickettsial drugs.

Aged↗
PubMed1989

Rickettsioses of the spotted fever group around the world.

Spotted fever group rickettsioses comprise Rocky Mountain spotted fever (Rickettsia rickettsii), boutonneuse fever (R. conorii), North Asian tick typhus (R. sibirica), Queensland tick typhus (R. australis), rickettsialpox (R. akari), and Oriental spotted fever (R. japonica). Ticks or mites serve as the vector and reservoir hosts of the rickettsiae. These obligate intracellular bacteria invade vascular endothelial cells, which are damaged directly, causing increased vascular permeability. The rash usually appears in Rocky Mountain spotted fever on the third day of illness and later evolves to become petechial maculopapules in 50% of cases with involvement of the palms and soles in a similar proportion of patients. Eschar occurs in some SFG rickettsioses at the site of tick bite, but rarely in Rocky Mountain spotted fever. Diagnosis often proves difficult, and laboratory assays for antibodies to SFG rickettsiae are generally useful only in convalescence. Rickettsiae are demonstrable by diagnostic immunohistology in biopsies of rash or eschar. Empiric treatment with doxycycline, tetracycline, or chloramphenicol should be given early in the course on the basis of clinical suspicion of the diagnosis of a SFG rickettsiosis.

Humans↗
PubMed1989

Rocky Mountain spotted fever: a disease in need of microbiological concern.

Rocky Mountain spotted fever, a life-threatening tick-transmitted infection, is the most prevalent rickettsiosis in the United States. This zoonosis is firmly entrenched in the tick host, which maintains the rickettsiae in nature by transovarian transmission. Although the incidence of disease fluctuates in various regions and nationwide, the problems of a deceptively difficult clinical diagnosis and little microbiologic diagnostic effort persist. Many empiric antibiotic regimens lack antirickettsial activity. There is neither an effective vaccine nor a generally available assay that is diagnostic during the early stages of illness, when treatment is most effective. Microbiology laboratories that offer only the archaic retrospective Weil-Felix serologic tests should review the needs of their patients. Research microbiologists who tackle these challenging organisms have an array of questions to address regarding rickettsial surface composition, structure-function analysis, and pathogenic and immune mechanisms, as well as laboratory diagnosis.

Animals↗
PubMed1988

Purification and characterization of a phosphatidylinositol kinase from A431 cells.

A phosphatidylinositol kinase from A431 cells has been purified to near homogeneity. Purification was achieved through the use of a combination of chromatography steps including affinity elution of the enzyme from a heparin-agarose column with PI. Characterization of the [32P]PIP formed by the purified PI kinase indicates that the enzyme phosphorylates the inositol on the 4-position and is therefore a phosphatidylinositol 4-kinase. The enzyme has a subunit weight of 55,000 as estimated by SDS gel electrophoresis and appears to be active as a monomer. Studies of the hydrodynamic properties of the enzyme indicate that the PI kinase binds substantial amounts of Triton X-100 and is actually present in detergent-containing solutions as a complex with a molecular weight of approximately 120,000. The Km of the enzyme for PI is 16 microM and for ATP is 74 microM. The enzyme is inhibited by adenosine with an IC50 of 100 microM. These properties are essentially identical with those of the membrane-bound PI kinase in A431 cells which is stimulated by EGF. The data therefore suggest that the EGF-stimulated PI kinase is a 55,000-Da monomer.

1-Phosphatidylinositol 4-Kinase↗
PubMed1988

Pathogenesis of rickettsial eschars: the tache noire of boutonneuse fever.

Prospective investigation of cutaneous lesions of 24 Sicilian patients revealed that 17 were taches noires from patients with a documented diagnosis of boutonneuse fever. Immunofluorescent Rickettsia conorii were demonstrated in 14 of 17 taches noires. The major pathologic lesions observed were a moderate-to-severe lymphohistiocytic vasculitis (17 of 17 cases), generally moderate dermal edema (17 of 17 cases), and cutaneous necrosis (12 of 16 cases). In contrast with previous observations of eschars in Rocky Mountain spotted fever, thrombosis was usually absent (nine of 17 cases) or inconsequential (five of 17 cases). Thus, it appears that the pathogenic mechanism of the ischemic necrosis is not thrombosis, suggesting either compression of the microcirculation by the dermal edema or another mechanism. Review of the biomedical literature related to eschars and cutaneous arthropod bites strongly argues against a pathogenetic contribution of the tick bite itself other than the intradermal inoculation of rickettsiae. The tache noire offers an excellent, accessible model for the study of the human-rickettsia interaction, including the pathogenic mechanisms leading to necrosis and the immune mechanisms resulting in killing the rickettsiae.

Adult↗
PubMed1988

Meningoencephalitis as a major manifestation of Rocky Mountain spotted fever.

Although our two patients had very different courses, both illustrate the gravity of rickettsial meningoencephalitis. The presence of neurologic signs and symptoms is ominous and should be recognized as a possible manifestation of Rocky Mountain spotted fever. A high index of suspicion for RMSF needs to be maintained in patients with an acute febrile illness, especially in endemic areas, even during periods other than "tick season," and in patients without a rash.

Brain↗
PubMed1988

Protective monoclonal antibodies recognize heat-labile epitopes on surface proteins of spotted fever group rickettsiae.

Thirty-eight monoclonal antibodies that have not been reported previously were developed from mice immunized with Rickettsia rickettsii, R. conorii, and R. sibirica. Western immunoblotting showed that these monoclonal antibodies are directed against heat-sensitive epitopes which are located on two major surface polypeptides with molecular sizes ranging from 115 to 150 kilodaltons. The detection of the two bands did not depend on the presence of 2-mercaptoethanol. Both bands were destroyed by treatment with proteinase K. Monoclonal antibodies examined by immunofluorescence assay reacted with epitopes that are species specific, group reactive, or shared among a smaller subset of species of spotted fever group rickettsiae. Nine of the monoclonal antibodies were evaluated for their ability to neutralize rickettsial infection and thus protect animals against disease caused by homologous species of rickettsiae. Treatment of rickettsiae with monoclonal antibodies F3-12, F3-14, and F3-36 completely protected guinea pigs against illness caused by the homologous organism R. rickettsii. Monoclonal antibodies F9-5G11 and F15-5B12, derived from mice immunized with R. sibirica, conferred partial protection by delaying the onset and shortening the duration of fever in guinea pigs inoculated with R. sibirica. Monoclonal antibodies F2-15, F2-31, F2-53, and F3-12 protected mice from a lethal infection with R. conorii. Heat-labile epitopes of spotted fever group rickettsial surface proteins are important candidate antigens for development of vaccines to confer protective immunity.

Animals↗
PubMed1988

Antigenic analysis of Chinese strains of spotted fever group rickettsiae by protein immunoblotting.

Protein immunoblotting demonstrated that 6 Chinese strains of spotted fever group (SFG) rickettsiae from northern China had antigenic polypeptides identical to those of Rickettsia siberica (strains 246 and 232), and dissimilar to other SFG rickettsiae. The various species of other SFG rickettsiae exhibited serologically distinct epitopes as well as many cross-reactive epitopes in protein immunoblotting. All SFG rickettsiae examined in this study had major antigenic polypeptides of 113-160 kDa.

Animals↗
PubMed1988

Clinical, hematologic, and humoral immune response in female dogs inoculated with Rickettsia rickettsii and Rickettsia montana.

Female Beagles were inoculated intradermally with a sublethal dose of Rickettsia rickettsii and R montana. Three dogs (group 1) were inoculated with 2 X 10(2) plaque-forming units (PFU) of R rickettsia and were treated with tetracycline beginning on postinoculation day (PID) 12; 3 dogs (group 2) were inoculated with 2 X 10(2) PFU of R rickettsii but were not treated; 3 dogs (group 3) were inoculated with 2 X 10(2) PFU of R montana. Group-3 dogs failed to seroconvert and were inoculated a second time on PID 68. Groups 1 and 2 dogs inoculated with R rickettsii became depressed and developed occasional inappetence, fever, hematochezia, and ocular lesions. These dogs had a decrease in PCV and RBC count, an initial decrease in WBC count followed by leukocytosis, and a decrease in platelet count. Group-3 dogs inoculated with R montana remained healthy. After R rickettsii inoculation, the serologic response to spotted fever group (SFG) rickettsial antigens (R rickettsii, R rhipicephali, R montana, and R bellii) was similar. The antibody response to R rickettsii was first detected on PID 9, with peak titers reached by PID 20. Serum titers to R rickettsii remained stable or decreased one dilution through PID 120. Of 4 SFG rickettsial antigens, the highest serologic response was to R rickettsii. A cross-reacting antibody response with R rhipicephali and R montana was nearly identical and was only slightly less than the response to R rickettsii. Cross-reacting antibodies to R belli were of lower mean titer and of shorter duration than were cross-reacting antibodies to other SFG rickettsiae.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Substrate specificity and kinetic mechanism of human placental insulin receptor/kinase.

The insulin receptor has been shown to be a protein kinase which phosphorylates its substrates on tyrosine residues. To examine the acceptor specificity of affinity-purified insulin receptor/kinase, hydroxyamino acid containing analogues of the synthetic peptide substrate Arg-Arg-Leu-Ile-Glu-Asp-Ala-Glu-Tyr-Ala-Ala-Arg-Gly were prepared. Substitution of serine, threonine, or D-tyrosine for L-tyrosine completely ablated the acceptor activity of the synthetic peptides. These peptides, along with a phenylalanine-containing analogue, did serve as competitive inhibitors of the insulin receptor/kinase with apparent Ki values in the range of 2-4 mM. These data suggest that the insulin receptor/kinase is specific for tyrosine residues in its acceptor substrate and imply that serine phosphate or threonine phosphate present in receptor is due to phosphorylation by other protein kinases. The kinetics of the phosphorylation of the L-tyrosine-containing peptide were examined by using prephosphorylated insulin receptor/kinase. Prephosphorylation of the receptor was necessary to maximally activate the kinase and to linearize the initial velocity of the peptide phosphorylation reaction. The data obtained rule out a ping-pong mechanism and are consistent with a random-order rapid-equilibrium mechanism for the phosphorylation of this peptide substrate. Additional experiments demonstrated that the autophosphorylated insulin receptor was not able to transfer the preincorporated phosphate to the synthetic peptide substrate. Thus, the insulin receptor/kinase catalyzes the reaction via a mechanism that does not involve transfer of phosphate from a phosphotyrosine-containing enzyme intermediate.

Binding, Competitive↗