The dermal delayed type hypersensitivity reaction in sheep naturally infected with maedi-visna virus

Maedi Visna virus (MVV) is the prototype lentivirus, capable of infecting cells of the monocyte/macrophage series in sheep. Infection is associated with pathological changes characterised by dysfunction of the cell mediated immune system. The work described in this thesis was undertaken to study in vivo cell mediated immune function in sheep infected with MVV using the tuberculin driven delayed type hypersensitivity (DTH) reaction as the experimental system.The gross and immunohistological characteristics of the DTH were firstly evaluated in control sheep (CD4+, CD8+, y8, and B lymphocytes, macrophages and MHC class II expression). Grossly, the reaction consisted of an indurative plaque, maximal in size at 48-72 hours post challenge. Histologically, there was an early infiltrate of polymorphonuclear neutrophils (PMNs), with a subsequent influx of CD4+ and CD8+ T cells. Macrophages and MHC class II bearing cells left the lesion at the later stages. In comparison, MVV infected sheep exhibited a reduction in the size of the gross DTH which was significantly associated with a decreased density of PMNs and CD4+ cells in the early reaction, but not with the degree of classical pathological change evaluated at subsequent post mortem or the presence of viral RNA in the skin.Depletion of circulating PMNs using cytotoxic drugs in control sheep resulted in the depression in the size of the DTH and a reduced influx of CD4+ cells, confirming the importance of PMNs in the development of the DTH lesion.The migratory ability of PMNs and CD4+ cells to the sites of dermally injected proinflammatory mediators (IL-8, TNF-a, and zymosan activated plasma) was subsequently shown to similar in control and MVV infected sheep.Evaluation of the levels of circulating anti-PPD antibodies in the MVV infected and control groups provided evidence for a negative association between antibody levels and DTH size suggesting a switch to a Th2 type response in the MVV infected sheepFinally, the presence of cytokine mRNA (IL-10, TNF-a, IFN-y and IL2-R) in the early lesions of both groups was assessed using reverse transcription polymerase chain reaction (RT-PCR) technology. This indicated that the mRNA expression pattern of these cytokines was not significantly different in control and MVV infected sheep.In conclusion, the work has shown a significant depression of the DTH response in sheep infected with MVV. This depression is associated with decreased density of PMNs and CD4+ cells in the early reaction, but is not associated with abnormalities in the trafficking of these cells to dermally injected proinflammatory mediators, the presence of antibody/antigen complexes, the presence of viral RNA, or difference in the cytokine mRNA production profile. The importance of the PMN in the DTH has been indicated, and a defect in the in vivo immune response of the PMN in MVV infected sheep has been described

The effect of buried fibres on offshore pipeline plough performance

Ploughing is a technique often used to bury offshore pipelines in the seabed. During this process the operator must ensure that a sufficiently deep, level trench is produced while towing the plough with the available bollard pull of a suitable trenching support vessel. This paper reports experimental work investigating the effect that encountering fibres or reinforcing elements such as buried tree branches in the soil (e.g. relict debris from deltaic flood washout) may have on the ploughing operation. It is shown that fibres in soil can have a reinforcing effect and hinder plough progress by both increasing tow force and leading to potential 'ride-out' of the plough (significant loss of trenching depth). This behaviour is correlated with the percentage of fibre reinforcement volume in sand and a simple method is provided to estimate changes in tow force and plough inclination during ploughing operations.</p

\u3ci\u3eAgropyron arizonicum\u3c/i\u3e (Gramineae: Triticeae) and a natural hybrid from Arizona

The new hybrid X Agrositanion pinalenoensis (Gramineae: Tribe Triticeae) is found in disturbed, forested areas of higher elevations in southern Arizona. In the Pinaleno Mountains where logging has been heavy, numerous disturbed habitats have permitted frequent hybrid populations to persist. Intermediate phenotype, chromosome behavior, lack of seed set, and pollen sterility were used to interpret the status of this hybrid derivative. Introgression and/or segregation are not apparent

Global Recognition of Qualified Toxicologic Pathologists: Credential Review as a Potential Route for Recognizing the Proficiency of Pathologists Involved in Regulatory-type Nonclinical Studies*

Recent international summits of the International Federation of Societies of Toxicologic Pathologists (IFSTP) have debated the desirability and potential means by which the proficiency of an individual toxicologic pathologist might be recognized and communicated throughout the world. The present document describes the advantages and disadvantages of implementing such a global recognition system by any means, and provides a proposal whereby recognition might be accorded via rigorous credential review of a practitioner’s education and experience