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Biomedical subjects

R Norrby

Publications and source records attributed to R Norrby.

84 records · Page 5Linked to original sources
PubMed1971

Immunological Study on the Host Cell Penetration Factor of Toxoplasma gondii.

The host cell penetration factor (PEF) of Toxoplasma gondii was studied by biochemical and immunological techniques. Sephadex gel filtration of an ammonium sulfate-precipitated PEF yielded two components with different molecular weight, but both having penetration-enhancing activity. The methods for purification removed at least 99.9% of extraneous protein. For demonstration of a significant enhancement of penetration, 0.001 mug of protein was sufficient. Biochemically, they appeared to be acid proteins with the same electrophoretic mobility. Both components showed maximal enhancement of penetration at pH 7.6 and 37 C. PEF antisera reduced the penetrative capacity of Toxoplasma parasites. The penetration-enhancing effect of the two components of PEF was inhibited by antiserum against any of them. Moreover, immunologically identical immunoprecipitates were obtained when antiserum reacted with the two components. The results thus indicated that the two components of PEF were immunogenically identical and that the difference in molecular weights might result from aggregation. Immunofluorescence indicated that PEF was related to cytoplasmic structures located in the anterior end of Toxoplasma. A possible relation between these structures and the paired organelle or the convoluted tubes was discussed. The number of parasites with immunofluorescence was low shortly after host cell penetration and increased during the intracellular life of the parasites after kinetics, previously observed for synthesis of PEF as well as for lysosomal activity of Toxoplasma.

Journal Article↗
PubMed1970

Host Cell Penetration of Toxoplasma gondii.

The host cell penetration of Toxoplasma gondii was studied with reference to synthesis of a penetration-enhancing factor and the penetrative capacity of the parasites during the various phases of the infectious cycle. HeLa cells as suspension or monolayer cultures were infected with Toxoplasma. After a lag phase shorter than 1 hr, there was a synthesis of penetration-enhancing factor demonstrable in the parasites. Exposure of the factor to host cells resulted in disappearance of its penetration-enhancing activity. The findings were in accord with the hypothesis that Toxoplasma gondii is capable of synthesizing an enzyme-like factor, reacting with the host cell surface, and, thereby, facilitating the penetration of the parasites. This hypothesis was further supported by the observations that the penetrative capacity of extracellular parasites gradually was reduced in presence of host cells and that intracellular parasites released artificially from host cells shortly after penetration were found to have a reduced penetrative capacity. Parasites allowed to remain for 4 hr or more intracellularly could restore and markedly improve their penetrative capacity.

Journal Article↗
PubMed1968

Penetration-enhancing factor extracted from Toxoplasma gondii which increases its virulence for mice.

Fractionation of extracts of disintegrated Toxoplasma gondii resulted in preparations which, when tested in cell cultures, enhanced penetration of host cells by this parasite. The influence of the preparations on the virulence of the RH strain and on two naturally avirulent strains for mice was studied simultaneously with the in vitro studies. It was demonstrated that the preparations increased the virulence of Toxoplasma. Mice inoculated with the preparation plus Toxoplasma suffered earlier morbidity and had a greater mortality rate than the control animals. There was a direct correlation between the effect of the preparations on the cell-penetrating capacity of the parasites and the increase in virulence for mice, indicating that the same mechanism is operative in both the in vivo and in vitro systems observed.

Animals↗
PubMed1968

Lysosomes of Toxoplasma gondii and their possible relation to the host-cell penetration of toxoplasma parasites.

Lysosome-like structures of Toxoplasma gondii were observed by means of vital staining with acridine orange and by the Gomori technique. These structures were found scattered over the cytoplasm but were often located at one end of the parasite. In comparison with parasites of the inoculum used for infecting HeLa cell cultures, the toxoplasma which had penetrated the HeLa cells revealed a markedly lower percentage of parasites showing lysosomal staining. After the penetration, the number of parasites with demonstrable lysosomes increased successively and, at the time for release of newly formed parasites (at 24 hr), the majority of the parasites demonstrated lysosome-like bodies in the cytoplasm. The observations are discussed with special reference to the mechanism of host-cell penetration.

Acridines↗
PubMed1967

Factors enhancing the host-cell penetration of Toxoplasma gondii.

The penetration into HeLa cells of Toxoplasma gondii was studied with a cell culture technique. The influence on the rate of penetration and the number of penetrating Toxoplasma parasites was tested by use of preparations of disintegrated parasites mixed with test parasites. These preparations were found to contain factors enhancing the penetrating rate of the parasites. This effect was demonstrable by use of untreated parasites as well as parasites lacking active motility owing to a previous exposure to Formalin. The preparations of disintegrated parasites contained, in addition, components inhibitory to the penetration-enhancing factors. These inhibitory components were able to reduce the penetrating capacity of normal Toxoplasma parasites, suggesting that the studied enhancing factors may play a role in the natural process of penetration. The efficacy of various techniques for disintegration of Toxoplasma parasites was investigated for release of penetration-enhancing factors from Toxoplasma parasites. The methods used resemble those used for liberation of lysosomal enzymes. Reduced osmotic pressure was obviously not adequate for release of enhancing factors, whereas the freezing and thawing procedure, sonic treatment, and irradiation produced high yields. It was difficult to evaluate the effect of incubation at acid pH on release of enhancing activity, because the penetration-promoting factors seemed unstable on both the acid and the alkaline sides of pH 7.6.

Freezing↗
PubMedDate not supplied

Penetration of newer cephalosporins into cerebrospinal fluid.

A review of the world literature on the penetration (ratio of concentrations of cerebrospinal fluid to concentrations of serum) and attainable antibiotic concentrations in the cerebrospinal fluid in humans for cefuroxime, cefoxitin, cefotaxime, ceftizoxime, cefmenoxime, cefamandole, cefoperazone, moxalactam, ceftazidime, and ceftriaxone indicates that, with the exceptions of cefamandole and cefoperazone, all agents appear equivalent. We conclude that the choice of cephalosporin for the treatment of acute bacterial meningitis should depend mainly on the potency of the agent for the specific meningeal pathogens in question. For the treatment of common meningeal pathogens (Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis) and for gram-negative bacilli, mainly Escherichia coli and Klebsiella (excluding Pseudomonas aeruginosa), the cefotaxime-ceftriaxone group of cephalosporins has accrued the most clinical experience and the most pharmacokinetic data, while for P. aeruginosa the major interest has centered on ceftazidime.

Animals↗
PubMedDate not supplied

Invasive pneumococcal infections: incidence, predisposing factors, and prognosis.

A retrospective analysis of the case records of 494 patients with 508 episodes of pneumococcal infections verified by cultures from blood or from cerebrospinal, pleural, and/or synovial fluid from 1964 through 1980 is presented and discussed in relation to the literature on invasive pneumococcal infections. The documented incidence (1976-1980) of pneumococcal meningitis in a defined area of southwestern Sweden was similar to that reported from the United States; 1.4 cases per 100,000 persons per year; for nonmeningitic infections (mainly bacteremic pneumonia) the incidence was 6.1 per 100,000 per year. The highest age-specific incidence was seen in infants younger than two years. In the vast majority of patients, predisposing conditions (young or old age or severe underlying diseases) were present. In adults, alcoholism was the most important risk factor. The fatality rate was 33% for patients with meningitis and 15% for patients with non-meningitic infections, figures that were strikingly similar to those reported in other studies. Underlying diseases and young or old age contributed significantly to the high mortality rates.

Adolescent↗