Biomedical subjects

S Cawley

Publications and source records attributed to S Cawley.

8 recordsLinked to original sources

PubMed1990

Cyclosporin A modulation of the acute inflammatory response: an explanation for the effect of CsA on host defences in infection.

Previous studies have shown that the administration of cyclosporin A (CsA) to animals with experimentally induced pyelonephritis resulted in considerable exacerbation of infection. T-lymphocytes are not involved in the host response to pyelonephritis but neutrophils are known to be a key component in the pathogenesis of this infection, so the effect of CsA on this inflammatory component was investigated. CsA administration did not affect the metabolic activity of neutrophils in vitro nor their ability to phagocytose and kill microorganisms. However, the ability of neutrophils to mobilize to a sterile inflammatory focus in vivo was significantly impaired. Further experiments, using models of pyelonephritis and subcutaneous infection, demonstrated that the CsA-induced suppression of neutrophil mobilization was directly related to the observed increase in bacterial numbers and exacerbation of tissue damage. Additionally, the actual effect of CsA on host defences and the outcome of infection was found to be dependent on the level of the initial infectious challenge. The results of this study provide an explanation for the current pattern of infectious disease in patients treated with CsA, in whom infection with extracellular pathogens is still common. It is also clear that the effect of CsA on inflammatory mechanisms may explain the efficacy of the agent in inflammatory diseases such as rheumatoid arthritis. This suggests a wider therapeutic role for CsA than is currently recognized.

Acute-Phase Reaction↗

PubMed1988

Peripheral blood leukocyte count as an index of defense status in the leukopenic host.

These experimental studies have investigated the reliability of the peripheral blood leukocyte count to predict whether the leukopenic host can contain or eliminate infection. Additionally, we have investigated the possibility that determination of leukocyte recruitment, supplementary to peripheral blood leukocyte counts, might allow individuals with neutropenia at risk from serious infection to be distinguished with greater certainty. Varying doses of radiation, cyclophosphamide, and methylprednisolone were used to induce distinct levels of leukopenia in rats. Leukocyte recruitment was measured by quantifying the response of neutropenic animals to evocative, subcutaneous stimuli, and the results of this assay were then compared with circulating leukocyte counts in the same individuals. Six models of experimentally induced infection were used to compare circulating and recruitable leukocytes as indicators of the susceptibility of the leukopenic host to infection. Response curves relating leukocyte numbers to host resistance were similar when circulating or recruitable leukocytes were used as an index of defense capability. These findings support the use of peripheral blood leukocyte numbers as an index of resistance to infection in individuals with leukopenia and suggest that functional analyses such as leukocyte recruitment are unlikely to provide additional information.

Animals↗

PubMed1987

Cellular basis of host defence in pyelonephritis. III. Deletion of individual components.

Hosts were depleted of individual cellular components to determine the effects of these manipulations on cellular defence mechanisms in acute and chronic pyelonephritis. T-lymphocytes were found to have little or no involvement in host protection but cyclosporin A administration had a dramatic effect on the gross pathology and bacteriological status of experimentally induced pyelonephritis. This change represented a major depression of host defence status. Cyclosporin A also activated resolved lesions in chronic pyelonephritis, associated with an increase in bacterial numbers. Administration of antineutrophil serum also led to a 1000-fold increase in bacterial numbers in the acute phase but had little effect on the host-parasite balance in chronic pyelonephritis. Macrophage blockade, on the other hand, did not affect the course of either acute or chronic infection. These studies have provided additional information on the immunobiology of experimental pyelonephritis and have focussed attention on the role of neutrophils, and an unidentified mechanism, affected by cyclosporin A, in host defence to renal infection.

Animals↗

PubMed1986

Sustained release of a corticosteroid using polymeric implants.

An effective sustained release method of drug administration, using methylprednisolone incorporated into acrylic bone cement, has been developed. The effect of this form of treatment on peripheral blood leukocytes, lymphoid tissue weight and the inflammatory response has been evaluated. This mode of methylprednisolone administration was compared with conventional systemic therapy and was found to produce rapid and prolonged pharmacological effects at very low plasma levels of drug. A dose response relationship was established and we determined that, for a given quantity of drug, the level and duration of suppression was greater using sustained release therapy. The inflammatory response was also depressed using this mode of administration. These results, coupled with the commercial availability and existing clinical approval of SIMPLEX P bone cement, suggest that further development may lead to useful clinical protocols.

Adrenal Cortex Hormones↗

PubMed1986

Cellular basis of host defence in pyelonephritis. I. Chronic infection.

Infection persists for long periods in chronic pyelonephritis, but the cellular basis of the host-parasite relationship is poorly understood. We have obtained quantitative data on the relationship between the pathogen (E. coli) and cellular defence mechanisms. Depletion of cellular components was carried out using whole body irradiation, methylprednisolone, cyclophosphamide or carrageenan and silica particles. A system of administering cyclophosphamide and methylprednisolone through the use of a slow release carrier, as well as graded doses of irradiation, was then developed to allow the controlled reduction of cellular competence. Quantitative studies in a host with chronic pyelonephritis and normal cellular defence reserves showed that severe depletion of granulocytic cells is necessary before host defence mechanisms are adversely affected. This finding conflicts with the observation that microorganisms survive and persist in the kidney for extended periods. Additionally, noncellular factors may also limit bacterial growth.

Animals↗

PubMed1986

Cellular basis of host defence in pyelonephritis. II. Acute infection.

We have investigated the cellular basis of host defence mechanisms in experimental pyelonephritis. Cellular components of the host defence system were depleted using cyclophosphamide, methylprednisolone or radiation. Depletion of cellular competence did not affect the course of infection during the first 16 h after challenge with Escherichia coli, but after 96 h up to a 1000-fold increase in bacterial numbers in the kidneys of cytodepleted animals was demonstrable. When quantitative aspects of the relationship between cellular competence and host defence were studied, it was found that severe depletion of cellular components was necessary before host defence mechanisms were adversely affected. Thus while cellular mechanisms are quantitatively adequate and contribute to host defence in pyelonephritis they have little impact on the immediate post-infection phase. Non-cellular factors however, do limit bacterial proliferation in the acute phase and may be important determinants in the biology of pyelonephritis.

Acute Disease↗

PubMed1985

Extended immunosuppression with cyclophosphamide using controlled-release polymeric implants.

An effective method of prolonged immunosuppressive therapy using cyclophosphamide incorporated into acrylic bone cement has been developed. We have studied the effect of this form of administration of cyclophosphamide on circulating immune cells and the inflammatory response. When the slow release mode of cyclophosphamide administration was compared with conventional systemic therapy, it was found to produce a more rapid and prolonged immunosuppression. A dose-response relationship was established and the biological effects of varying the composition and surface area of the implant were determined. The inflammatory response, assessed by measuring the mobilisation of cells into subcutaneously implanted sponges, was also depressed using this mode of administration. These results, coupled with the commercial availability and existing clinical approval of Simplex P bone cement, suggest that the procedure could lead to useful clinical protocols.

Animals↗

PubMed1985

Immunopotentiation in infectious disease, I. Effect of bestatin on the immune response.

Few immunomodulators are available for the control of infectious disease. One reason has been the lack of a suitable protocol for evaluating such agents. We have presented a series of assays of immune function that will allow a standardized approach to this problem. The value of this protocol has been established using long-term low dose, and short-term high dose, administration of bestatin, a small molecular weight microbial product. The experiments were done using both normal and immunocompromised animals. Bestatin had no effect on circulating leukocytes or the reticuloendothelial system. Leukocyte mobilization and T cell responsiveness in immunocompromised animals were enhanced following bestatin treatment. The antibody response to SRBC doubled in normal animals while the same treatment schedule resulted in a marked reduction in the response to Escherichia coli lipopolysaccharide. These results have established the value of the protocol and identified some new immunomodulating properties of bestatin which may be useful in the control of infectious disease.

Adjuvants, Immunologic↗