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Biomedical subjects

G Knowles

Publications and source records attributed to G Knowles.

At least 37 records · Page 2Linked to original sources
PubMed1991

Discrimination of two fibroblast progenitor populations in early explant cultures of hamster gingiva.

Numerous metabolic studies have demonstrated heterogeneity of fibroblast populations in culture, yet little is known about the structure of fibroblast populations in adult tissues in vivo. To determine if populations of both cycling and non-cycling cells are present in gingiva, hamsters were labelled with [3H]-thymidine to label cycling cells in vivo, and explanted biopsies were subsequently incubated with bromodeoxyuridine to label cycling cells in vitro. Cycling cells were identified by combined immunohistochemistry and radioautography. Fibroblasts were recognized by the presence of vimentin and the absence of keratin as determined by immunofluorescence. The largest proportion of cells were double-labelled with [3H]-thymidine and bromodeoxyuridine (43.8%) indicating the presence of actively cycling populations that maintained their proliferative status upon explanation. Cultures also exhibited a second population of cells labelled only with bromodeoxyuridine (38.7%) that did not cycle in vivo, but retained the capacity for proliferation in vitro. However, limiting dilution analysis of single-cell suspensions revealed only a single class of progenitors capable of forming large colonies in vitro. Approximately 1 in 190 plated cells was capable of colony-formation, indicating that, upon explanation, a subset of the cycling cells in vitro exhibits extensive proliferative capacity. There was also a small population of cells unlabeled with either [3H]-thymidine or bromodeoxyuridine (9.4%) that appeared to be terminally differentiated. Different substrates, including glass and thin films of gelatin and collagen, did not significantly alter the fraction of cells labelled with [3H]-thymidine. These data demonstrate the existence of 2 separate progenitor-cell populations with different capacities for proliferation in vivo and in vitro.

Animals↗
PubMed1991

Variation in resistance to isometamidium chloride and diminazene aceturate by clones derived from a stock of Trypanosoma congolense.

Nine clones were derived from a drug-resistant Trypanosoma congolense stock (IL 2856) and characterized in mice for their sensitivity to isometamidium chloride and diminazene aceturate. All clones were derived from the stock without drug selection and expressed high levels of resistance to isometamidium chloride (50% curative dose [CD50] values ranging from 1.5 to 5.1 mg/kg) and intermediate to high levels of resistance to diminazene aceturate (CD50 values ranging from 5.1 to 21.0 mg/kg). By contrast, the isometamidium chloride and diminazene aceturate CD50 values for a drug-sensitive clone, T. congolense IL 1180, were 0.018 mg/kg and 2.3 mg/kg, respectively. For both drugs, there appeared to be significantly different levels in expression of drug resistance amongst the 9 clones derived from IL 2856. Isoenzyme analysis of 7 enzymes showed that all 9 clones expressed the same electrophoretic variants. Thus, all 9 clones were identical for these phenotypic markers. The clone which expressed the highest level of resistance to isometamidium in mice (IL 3270) was transmitted to Boran cattle via the bite of infected Glossina morsitans centralis. IL 3270 produced an infection rate in tsetse of 5.0%. The resulting infections in cattle were shown to be resistant to intramuscular treatment with 2.0 mg/kg isometamidium chloride and 14.0 mg/kg diminazene aceturate. This contrasts with doses of 0.25 mg/kg isometamidium chloride or 3.5 mg/kg diminazene aceturate which are deemed sufficient to cure fully sensitive infections. Finally, 9 clones (subclones) were derived from IL 3270 and characterized in mice for their sensitivity to isometamidium chloride.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Role of the cellular attachment domain of fibronectin in the phagocytosis of beads by human gingival fibroblasts in vitro.

To study the role of phagocytosis in periodontal tissues, internalization of fibronectin-coated latex beads by Gin-1 fibroblast populations was investigated. Demonstration of phagocytosis by internalization of beads was confirmed by immunofluorescence microscopy, electron microscopy, and flow-cytometry. The percent of cells phagocytosing beads measured by flow-cytometry was negligible at 4 degrees and 23 degrees C, but increased to approximately 17% at 37 degrees C. As measured by automated image analysis, the percentage of phagocytosing cells increased linearly from 8 to 22 with increasing fibronectin concentration of the incubation solution from 30 ng to 300 micrograms/ml. Similar linear increases in the percentage of phagocytosing cells were observed when beads were incubated with cells for periods ranging from 2 h to 2 days. To examine the role of the Arg-Gly-Asp receptor in mediating phagocytosis, fibronectin-coated beads were first coated with either Gly-Arg-Gly-Asp-Ser-Pro or Gly-Arg-Gly-Glu-Ser-Pro peptides at concentrations of 0.125, 0.5, and 1 mg/ml, or with control vehicle, and then incubated with cells. Phagocytosis was completely blocked at 1 mg/ml of the Gly-Arg-Gly-Asp-Ser-Pro peptide, but the Gly-Arg-Gly-Glu-Ser-Pro peptide showed no significant inhibition compared to control values. Blocking antibodies to the cell attachment domain of the fibronectin molecule also reduced the percentage of phagocytosing cells significantly. The data show that these phagocytic assays are sensitive enough to detect the influence of incubation temperature and time, cellular heterogeneity, ligand type, and ligand concentration on the percentage of phagocytosing cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Adhesion↗
PubMed1990

A comparison of the isoenzymes of Trypanosoma (Duttonella) vivax isolates from East and West Africa.

The genetic diversity in 13 stocks and clones of Trypanosoma vivax from East and West Africa was compared by isoenzyme analysis. The Ugandan and West African stocks and clones showed a very high degree of genetic similarity to each other but they differed from the Kenyan stocks and clones. Two haemorrhagic stocks, IL 2337 (Galana, Kenya) and IL 3067 (Bamburi, Kenya), showed a high degree of similarity in enzyme banding patterns in electrophoresed preparations. One of the Kenyan stocks, M1D 627, differed in most of its enzyme banding patterns from all the other stocks and clones used.

Africa, Eastern↗
PubMed1990

Identification of activated T lymphocytes and eosinophils in bronchial biopsies in stable atopic asthma.

We have used immunohistochemistry and monoclonal antibodies to analyze the phenotypic composition and activation status of the cellular infiltrate of bronchial biopsies obtained by fiber optic bronchoscopy of 11 atopic asthmatic subjects (FEV1% predicted range 78 to 114), 9 atopic nonasthmatic control subjects, and 10 normal healthy subjects. Examination of mucosal biopsies obtained from both central (level I) and subsegmental (level II) bronchi showed that the highest number of CD45-, DC3-, DC4-, and CD8-positive cells were found in the group with asthma. There was a significant increase in the number of interleukin-2 receptor (CD25)-positive cells (a marker of lymphocyte activation) at airway level I in the asthmatic group compared with both nonasthmatic atopic (p less than 0.05) and normal control subjects (p less than 0.01). Eosinophil numbers were significantly increased in asthma at both airway levels and at airway level II in the nonasthmatic atopic group when compared with normal healthy control subjects (p less than 0.05). EG2-positive cells (an index of secretion of eosinophil cationic protein following activation) were found at both airway levels in the asthmatic group and at level I in the nonasthmatic atopic control group (p less than 0.05). When asthmatic subjects were compared with normal healthy subjects, there was a reduction in the number of neutrophil elastase-positive cells in the asthmatic subjects which, as a percentage of leukocytes, was significant (p = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Detection of parasite peptidase in the plasma of heifers infected with Trypanosoma congolense.

Plasma samples from heifers infected with Trypanosoma congolense were shown to contain a parasite peptidase. In some instances, trypanosome peptidase was detected in plasma samples taken from heifers for up to 14 days after infections had been successfully treated with diminazene aceturate (Berenil). Trypanosome peptidase was detected in plasma using starch gel electrophoresis and also by a dot blot assay in which a McAb, raised against the enzyme, was spotted onto nitrocellulose filters which were then used to absorb enzyme from the samples. The molecular weight of the enzyme was approximately 60,000. The possible role that a trypanosome peptidase may play in inducing pathology and its use in the diagnosis of infection and disease are discussed.

Animals↗
PubMed1988

Genetically discrete populations of Trypanosoma congolense from livestock on the Kenyan coast.

Twenty-seven stocks of Nannomonas trypanosomes isolated from livestock in 1982 on a ranch at Kilifi on the Kenyan coast were characterized by isoenzyme electrophoresis and by the abilities of the parasite's DNA to hybridize to two repetitive sequence DNA probes. All the Kilifi stocks which were examined had isoenzyme patterns which were markedly different from the 75 patterns previously described from 78 stocks of Trypanosoma congolense. On average only 15% of the enzyme bands present in the Kilifi stocks were present in those stocks of T. congolense which had previously been surveyed for isoenzymes. The DNA from all the Kilifi stocks which had been examined for isoenzymes hybridized with only the repetitive sequence probe isolated from a clone of a Kilifi stock. In contrast, the DNA from all 27 Kilifi stocks failed to hybridize with a repetitive sequence probe isolated from a clone from a different stock of T. congolense. Thus, the trypanosomes in all the Kilifi stocks examined were both phenotypically and genotypically discrete. These genetically discrete trypanosomes have also been detected in 2 stocks isolated from livestock from another location on the Kenyan coast. The results show that there is a wide range of genetic heterogeneity within the trypanosomes currently classified as T. congolense. We suggest that the limits of this genetic heterogeneity could represent incipient speciation.

Animals↗
PubMed1987

Peptidase in the plasma of mice infected with Trypanosoma brucei brucei.

The plasma of mice infected with pleomorphic Trypanosoma brucei brucei contains a peptidase which has the same electrophoretic mobility on starch gels as a parasite peptidase. An enzyme with this electrophoretic mobility was not detected in the plasma of uninfected mice. The molecular weight of this enzyme in either parasite lysate or plasma from infected mice was approximately 40,000 Da when assayed on a size exclusion column using high-performance liquid chromatography. The enzyme can cleave the dipeptides leu-ala, val-leu and pro-leu, but not the dipeptide phe-ala. The enzyme also cleaved the tripeptides tyr-tyr-tyr and leu-gly-gly. Another parasite peptidase which migrates on starch gels to a different position than the above-mentioned peptidase cleaved the dipeptides leu-ala, val-leu and pro-leu but could not cleave the tripeptides tyr-tyr-tyr or leu-gly-gly. Furthermore, incubation of this parasite peptidase with normal mouse plasma at 37 degrees C resulted in an apparent loss of detectable activity. It is postulated that the plasma of mice modifies either the charge or enzymic activity of this peptidase. We speculate that the parasite peptidase present in the plasma of mice infected with T. brucei could contribute to pathogenesis.

Animals↗
PubMed1984

The relationship between the in vitro response of Plasmodium falciparum to chloroquine, quinine and mefloquine.

We have measured the in vitro response of several isolates of Plasmodium falciparum to chloroquine, quinine and mefloquine. We show that parasites which are resistant to chloroquine also have a reduced sensitivity to quinine. However, there appears to be no correlation between chloroquine resistance and reduced sensitivity to mefloquine. We conclude that the emergence and spread of chloroquine resistance could also be establishing a population of parasites with a reduced sensitivity to quinine which may provide the basis for the eventual emergence of quinine resistance.

Animals↗
PubMed1984

Studies of antigens in Plasmodium yoelii. I. Antigenic differences between parasite lines detected by crossed immunoelectrophoresis.

Antigens of three lines of the rodent malaria parasite Plasmodium yoelii have been studied using crossed immunoelectrophoresis. P. y. yoelii line A1 is a mild line which is restricted to reticulocytes. P. y. yoelii line YM and P. y. nigeriensis line D1 are virulent infections which multiply in both immature and mature erythrocytes. One antigen, designated Py-1, was found to differ in its electrophoretic mobility between the lines, being fast (F) in lines A1 and YM and slow (S) in line D1. Antigen Py-1 also varied in quantity among the three lines; greater amounts were detected in parasites inhabiting mature erythrocytes than in those in reticulocytes. These characters were stable during blood and mosquito passage.

Anemia↗
PubMed1984

Studies of antigens in Plasmodium yoelii. II. Inheritance and recombination of antigenic characters.

The inheritance of an antigen designated Py-1 in the rodent malaria parasite Plasmodium yoelii has been investigated. A cross was made between 2 lines differing in the electrophoretic mobility and quantity of Py-1 detected by crossed immunoelectrophoresis. In 10 clones isolated from the progeny of the cross the level of Py-1 always correlated with the virulence of the infection and it was concluded that these characters were different phenotypic effects of the same gene mutation. The electrophoretic mobility of Py-1 segregated independently of the virulence character and was therefore controlled by a different gene. These two antigenic markers also recombined with isoenzyme and drug-sensitivity characters distinguishing the parent lines.

Animals↗
PubMed1984

Antigenic diversity found in isolates of Plasmodium falciparum from Papua New Guinea by using monoclonal antibodies.

Monoclonal antibodies were used to demonstrate antigenic diversity in over 100 primary isolates of Plasmodium falciparum collected from one area of Papua New Guinea. The frequencies of several parasite antigens in our sample is calculated. One particular antigen which had previously been shown to be absent in one-third of established isolates collected from several countries appeared ubiquitous in our sample from Papua New Guinea. A method is presented that can be used to test for associations between antigens; the analysis also reveals whether other variables affect these associations. Several associations between antigens were revealed. In one instance, the association between two particular parasite antigens was affected by the donor's age. The importance of characterizing the antigenic structure of P. falciparum populations, and its relevance to the introduction of an antimalarial vaccine are discussed.

Aging↗
PubMed1983

The use of computerized learning in intensive care: an evaluation of a new teaching program.

A computer-assisted learning program in respiratory intensive care was introduced into the undergraduate curriculum at University College Hospital. Educational effectiveness was assessed. This method of learning was found to be highly acceptable to students. The improvement in students knowledge of the subject was up to three times greater in those who used the computer program, than a control group of students who received only teaching by conventional means, (P = 0 X 016). The results of a questionnaire designed to elicit students' attitudes to this learning experience are discussed.

Anesthesiology↗
PubMed1983

Differential effect of immunoglobulin on the in vitro growth of several isolates of Plasmodium falciparum.

Immunoglobulin isolated from the sera of individuals living in a malarious area of Papua New Guinea was tested for an effect on the growth in vitro of four isolates of Plasmodium falciparum, three from Papua New Guinea and one from Thailand. The Papua New Guinea isolates were inhibited to the same degree by individual immunoglobulin preparations, and inhibition varied from 0 to 98% (assessed by a radioisotopic readout). Immunoglobulin preparations which inhibited the Papua New Guinea isolates caused less inhibition of the Thai parasites. Biosynthetically labeled parasite proteins were analyzed by two-dimensional gel electrophoresis, and differences were detected in the protein and antigenic composition of isolates which differed in their sensitivity to inhibitory immunoglobulin. Three acidic proteins (Mr 200,000, 150,000, and 65,000) were found only in the Papua New Guinea isolates. All Papua New Guinea isolates contained a high-molecular-weight basic protein with an Mr of 220,000 (Pf220), but the corresponding protein of the same molecular weight in the Thai isolate had a more acidic isoelectric point. Another isolate (from Africa) initially showed a degree of resistance to inhibition by Papua New Guinea immunoglobulin (although not to the same extent as the Thai parasite), but in later experiments, this isolate was susceptible to inhibition. During the course of this series of experiments, the antigenic composition of this (uncloned) isolate changed so that it became similar (but not identical) to the Papua New Guinea isolates.

Animals↗