PubMed Health⌕ Search

Biomedical subjects

I R Tizard

Publications and source records attributed to I R Tizard.

At least 55 records · Page 3Linked to original sources
PubMed1978

The generation of phospholipase A and hemolytic fatty acids by autolysing suspensions of Trypanosoma congolense.

When T. congolense undergoes autolysis there is a concomitant appearance of phospholipase A activity and hemolytic fatty acids. The generation of enzyme activity is exponential, and the appearance of hemolytic activity corresponds to a free fatty acid concentration of 0.02 to 0.03 mg. per ml. The concentration of the trypanosome suspension markedly affected the kinetics of the generation process. In contrast, the autolysis of T. lewisi did not generate hemolytic activity unless exogenous phospholipase A was added to the organisms.

Autolysis↗
PubMed1978

The immunosuppressive and mitogenic effects of Trypanosoma musculi.

In CD-1 mice infected with Trypanosoma musculi, the production of IgM and IgG antibodies in response to sheep erythrocytes (SRBC) was significantly suppressed when mice were immunized with SRBC once high parasitaemias had developed. In infected mice which were not immunized with SRBC, background plaque-forming responses of spleen cells to SRBC were significantly higher than in uninfected, unimmunized mice. Factors derived from T. musculi were found to be mitogenic in vitro for spleen cells taken from CD-1 mice. The mitogenic response to these factors by spleen cells from athymic mice was highly significant, whereas the response of spleen cells taken from CD-1 mice which had been pre-treated with cyclophosphamide was much less, suggesting that the B cell was the major target of the trypanosome-derived mitogen. In this paper we discuss the possible relationship of T. musculi-induced mitogenesis to the immunosuppression and non-specific antibody formation associated with T. musculi infections.

Animals↗
PubMed1978

Mechanisms of the anemia in trypanosomiasis: studies on the role of the hemolytic fatty acids derived from Trypanosoma congolense.

Trypanosoma congolense releases a number of hemolytic free fatty acids on autolysis of which the most potent is linoleic acid. These fatty acids can lyse washed rat and bovine erythrocytes in vitro. Autolysed T. congoleuse will cause increased fragility of erythrocytes in whole rat blood but not in whole bovine blood. The lack of effect of these fatty acids on bovine erythrocytes tends to be confirmed by the failure of this material to influence the survival of these cells in vivo. Calculations based on the amount of free fatty acids required to cause hemolysis in vivo also confirm that this mechanism of erythrocyte destruction is probably unimportant in bovine trypanosomiasis.

Anemia↗
PubMed1978

The prevalence of serum antibodies to Toxoplasma gondii in Ontario mammals.

The prevalence of seropositive reactions to Toxoplasma gondii was studied in farm animals, companion animals, wild rodents and birds. Of the animals tested, 17% of cattle, 65% of sheep, 45% of pigs, 9% of horses, 33% of dogs and 20% of cats were seropositive by the Sabin-Feldman dye test. In addition 11% of mice (Mus musculus), 5% of deer mice (Peromyscus), 3% of rats (Rattus norvegicus) and less than 2% of sparrows (Passer domestcus) were seropositive. All samples from short-tailed field mice (Microtus pennsylvanicus), squirrels (Sciurus carolinensis), chipmunks (Tamias striatus), meadow jumping mice (Zapus hudsonius) and starlings (Sturnus vulgaris) were seronegative. The significance of these findings in relation to the epizootiology of toxoplasmosis in Ontario is discussed.

Animals↗
PubMed1978

The absence of Trypanosoma congolense from the lymph of an infected sheep.

The lymph draining the prefemoral lymph node of a sheep infected with Trypanosoma congolense was examined over a period of 10 days. Only six trypanosomes were detected in 1500 ml of this fluid during this time, in spite of the animal having about 65,000 organisms/ml in its blood. It is concluded that the suggestion that T congolense is a strict plasma parasite is essentially proven for this specific situation.

Animals↗
PubMed1977

Free fatty acids, complement activation, and polyclonal B-cell stimulation as factors in the immunopathogenesis of African trypanosomiasis.

Human and animal forms of African trypanosomiasis are characterised by sustained hypocomplementaemia, gross hypergammaglobulinaemia M, and profound immunosuppression. It is suggested that this hypocomplementaemia is probably due to the action of a trypanosome-derived complement-activating factor and that the elevated IgM levels may be the combined result of this decomplementation, together with a subsequent failure of the normal IgM-to-IgG antibody switch mechanism and polyclonal B-lymphocyte activation by a trypanosome-generated mitogen. The immunosuppression in this disease may be a result of the collective immunosuppressive effects of trypanosome-derived immune-modulating free fatty acids, polyclonally stimulating B-cell mitogen, and complement-activating factors.

Animals↗
PubMed1977

The generation and identification of the hemolysin of Trypanosoma congolense.

The hemolytic activity of Trypanosoma congolense appears to be due to the presence of free fatty acids generated by the action of phospholipase A on endogenous phosphatidyl choline. Some lysolecithin also contributes to the lytic activity. Trypanosoma lewisi, being devoid of phospholipase A, does not generate free fatty acids and is therefore non-hemolytic.

Animals↗
PubMed1977

Toxocaral larva migrans: the use of larval secretory antigens in haemagglutination and soluble antigen fluorescent antibody tests.

Toxocara larval excretions and secretions collected from in vitro culture were used as antigen in passive haemagglutination and soluble antigen fluorescent antibody tests for the diagnosis of visceral larva migrans in experimental animals and man. Antibody to toxocaral secretions was detected in rabbits within 13 days of light Toxocara infection (ten larvae per kg) and within four days of heavy infection (10(4) larvae). Antibody was not detected following infection with 10(4) Ascaris suum larvae. In human sera, antibody was detected at low titre in 1% of 100 healthy adults and in 2% of 50 children. High titres were observed in one third of 170 patients with suspected visceral larva migrans and in 23 of 27 such patients presenting with an eosinophilia greater than 20%. In 25 patients with ocular lesions of an undiagnosed nature, four showed significant levels of anti-Toxocara antibody.

Adult↗
PubMed1977

The release of soluble vasoactive material from Trypanosoma congolense in intraperitoneal diffusion chambers.

Millipore diffusion chambers containing living or lysed Trypanosoma congolense cause a local inflammatory reaction when implanted intraperitoneally into rats. Empty chambers do not do this. The active material is of low molecular weight and is possibly peptide in nature. It appears to act by increasing local vascular permeability. It was found to be neither chemotactic nor cytotoxic in several assay systems. It is considered that this material may contribute to the pathogenesis of T. congolense infection in animals.

Animals↗
PubMed1977

The prevalence and epidemiology of toxoplasmosis in Ontario.

The results of testing 7060 human serum specimens obtained in the Province of Ontario, Canada, were analysed for the presence of antibodies to Toxoplasma gondii. Of these samples 38% were serologically positive at a titre of 1/16 or greater. The age-specific rates climbed from 2.7% in infants between 6 months and 1 year of age, to about 50% in individuals aged 25 years or over. Variations in prevalence were noted between different areas within the province and evidence is put forward to show that an inverse relation exists between urban size and toxoplasma prevalence. Seasonal and annual variations were not shown to be significant. On the basis of a very small sample of specimens, cat ownership not appear to cause a significant increase in the risk of acquiring this infection.

Adolescent↗
PubMed1976

The generation of toxic activity from trypanosoma congolense.

Trypanosoma congolense organism, on incubation at 20 degrees C for 91/2h, were found to generate phospholipase like activity which was capable of mediating lysis of both nucleated cells and erythrocytes as well as acute inflammatory response on intradermal inoculation.

Animals↗
PubMed1976

Some observations on the epidemiology of toxoplasmosis in Canada.

Between 1961 and 1974, 11934 samples of serum were tested by the Sabin-Feldman Dye test for the presence of antibodies to Toxoplasma gondii. Analysis of high-titred sera suggested that a 6-year cycle of high disease prevalence occurred across Canada. In addition, a decline in the percentage of positive reactions each year in the Fall. The suggestion that this decline was due to dry conditions during the summer months was supported by the observation that differences in the prevalence of toxoplasma infection in ten Canadian cities were related to their average summer rainfall. The significance of these observations in relation to the epidemiology of toxoplasmosis in this country is discussed. The influence of patient age on the prevalence of infection was also investigated; the results obtained suggested that at least 75% of infants with high antibody titres against T. gondii had obtained these antibodies by placental transfer from their mothers.

Adolescent↗
PubMed1976

Studies on the anemia in experimental African trypanosomiasis. II. The pathogenesis of the anemia in calves infected with Trypanosoma congolense.

It was postulated that the anemia commonly seen in mammalian trypanosomiasis, and specifically in Trypanosoma congolense-infected calves, was of immunological origin. Specifically, we postulated that trypanosome antigen-antibody-complement complexes, deposited on the surface of erythrocytes of infected calves, resulted in their immune elimination leading to clinical anemia. This hypothesis was tested experimentally. Immunoglobulins bound to the erythrocytes of 13 infected calves were detected by a direct antiglobulin test from 7 to 10 days post infection. The reaction was strongest between 3 and 9 weeks and remained inconsistently positive until the calves were killed by euthanasia 15 to 18 weeks after infection. Erythrocytes reacting positively in this test were then lysed and immunoglobulins were eluted from the washed stromata by means of the low pH buffer. Sixteen out of 74 eluates prepared in this way and concentrated, contained IgM and IgG. Antibody activity of these eluates against T. congolense was demonstrated by means of the complement fixation test, the indirect hemagglutination test, and the indirect antiglobulin test. It is considered that the original hypothesis has been essentially proven.

Anemia↗
PubMed1976

The prevalence of antibodies against Toxoplasma gondii in some Ontario mammals.

A survey of serum samples from mammals trapped in Central Ontario showed that many contained antibodies to Toxoplasma gondii. The prevalence of infection as reflected by positive reactions in the Sabin-Feldman Dye Test appeared to be related to the type of diet of each species examined, and specifically, to the proportion of rodents in the diet. Of the fox blood samples tested, 84% were positive. The percentage of positive samples diminished through, coyote, mink, bear, fisher skunk, raccoon, marten and rabbit. Blood samples from squirrel, deer, hare and groundhog were negative.

Animals↗