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This paper discusses how best to develop the educational platforms that can foster a wider appreciation of the importance of the One Health concept in medical and veterinary education. There are many compelling examples, from genetics to infectious diseases, where significant advances have been made in medicine and veterinary medicine by applying the principles of One Health, i.e. by recognising the interconnectedness between medicine, veterinary medicine and related sciences. In the medical and veterinary curriculum the objective should be to ensure that all opportunities are taken throughout preclinical and clinical teaching to incorporate the lessons which have been learned from the success stories in One Health. This will ensure that advances continue to be made and that a more pervasive and forward-looking scientific culture sustains One Health in the future.

Transmissible spongiform encephalopathies (TSEs) may be acquired peripherally, in which case infectivity usually accumulates in lymphoid tissues before dissemination to the nervous system. Studies of mouse scrapie models have shown that mature follicular dendritic cells (FDCs), expressing the host prion protein (PrP(c)), are critical for replication of infection in lymphoid tissues and subsequent neuroinvasion. Since FDCs require lymphotoxin signals from B lymphocytes to maintain their differentiated state, blockade of this stimulation with a lymphotoxin beta receptor-immunoglobulin fusion protein (LT beta R-Ig) leads to their temporary dedifferentiation. Here, a single treatment with LT beta R-Ig before intraperitoneal scrapie inoculation blocked the early accumulation of infectivity and disease-specific PrP (PrP(Sc)) within the spleen and substantially reduced disease susceptibility. These effects coincided with an absence of FDCs in the spleen for ca. 28 days after treatment. Although the period of FDC dedifferentiation was extended to at least 49 days by consecutive LT beta R-Ig treatments, this had little added protective benefit after injection with a moderate dose of scrapie. We also demonstrate that mature FDCs are critical for the transmission of scrapie from the gastrointestinal tract. Treatment with LT beta R-Ig before oral scrapie inoculation blocked PrP(Sc) accumulation in Peyer's patches and mesenteric lymph nodes and prevented neuroinvasion. However, treatment 14 days after oral inoculation did not affect survival time or susceptibility, suggesting that infectivity may have already spread to the peripheral nervous system. Although manipulation of FDCs may offer a potential approach for early intervention in peripherally acquired TSEs, these data suggest that the duration of the treatment window may vary widely depending on the route of exposure.

Reactive changes occurring within lymph nodes draining the subcutaneous site of acute infection with maedi-visna virus (MVV) were studied, and the appearance of infected cells correlated with the immune response. Cells infected with virus were detected in the node by cocultivation from day 4 postinfection (p.i.), with maximum numbers being seen between days 7 and 14, but even then infected cells were rare, with a maximum frequency of 23 50% tissue culture infective doses (TCID50) in 10(6) lymph node cells. At later times, infected cells were still detected, but their numbers fell to 1 to 2 TCID50 per 10(6) cells. Virus-specific CD8+ cytotoxic T-cell precursors (CTLp) were isolated from infected nodes from day 10 p.i. onwards, and T-cell proliferative responses to MVV were first detected on day 7 and consistently detected after day 18. Histological analysis showed a vigorous immune response in the node. There was a marked blast reaction in the T-cell-rich zones, which was greatest at the time when the number of virally infected cells was at its height. At this stage, large numbers of plasma cells were seen in the medullary cords, indicating that extensive T-cell-dependent B-cell activation was occurring in the T-cell-rich zones. Germinal centers were prominent shortly after the onset of the T-zone response and were still present at 40 days p.i. Phenotype studies of isolated lymph node cells failed to detect major changes in the proportion or phenotype of macrophages, CD1+ interdigitating cells, and CD4+ or CD8+ T cells despite the fact that CD8+ lymphoblasts form a major population leaving the node in efferent lymph. This suggests that there is a balanced increase in the number of all cell types in response to the virus within the node and selective migration of CD8+ lymphoblasts containing virus-specific CTLp from the node. Virus-specific immune responses are therefore present within the node when infectious virus isolation is maximal, but cellular immunity may act to control the level of infection from day 18 onwards.

We have investigated several aspects of gamma delta T cells in sheep. gamma delta T cells of sheep express a unique transmembrane protein termed T19 but lack the expression of particular cell-surface molecules such as CD2, CD4 and CD8 which are typically associated with alpha beta T cells. The majority of gamma delta T cells isolated from animals of all ages examined lacked the expression of CD45RA. A faster rate of activation by gamma delta T cells compared to either CD4 or CD8 T cells was seen in the time-course of IL-2 receptor alpha chain (CD25) cell-surface expression. All gamma delta T cells expressed the CD25 protein within 8 hr of activation whereas the majority of CD4 or CD8 T cells did not express CD25 until 24 hr post-concanavalin A (Con A) stimulation. This difference in the rate of expression of activation molecules was not restricted to CD25, as a similar trend was seen with cell-surface expression of major histocompatibility complex (MHC) class II molecules. We have used the distinct phenotypic profile of ovine gamma delta T cells to purify these cells by positive selection via the T19 molecule to assess their in vitro proliferative response to various antigens. Routinely, cell populations comprising more than 93% gamma delta T cells with yields of approximately 55% were obtained. Purified gamma delta T cells were capable of responding to Mycobacterium tuberculosis antigen in a primary and secondary in vitro proliferation assay and to ovalbumin in a secondary response. Ovine gamma delta T cells showed little, if any, proliferative response to allogeneic stimulator cells.

The antidiuretic (V2) agonist, dDAVP, stimulates release of the clotting factors von Willebrand factor (vWF) and factor VIIIc (FVIIIc) in humans. The objective of these studies was to identify and characterize dDAVP stimulation of clotting factor release in pentobarbital-anesthetized rhesus monkeys using V2 receptor agonists (dDAVP, SKF 101926, SKF 104146, SKF 104244) and a V2 receptor antagonist (SKF 105494) given i.v. dDAVP (3.0 micrograms/kg) stimulated release of vWF, FVIIIc and renin and was associated with tachycardia and blood pressure-lowering activity. The V2 receptor antagonist, SKF 105494 (30 micrograms/kg, i.v.), had no effect on clotting factor release, heart rate or blood pressure, but prevented dDAVP stimulation of clotting factor release and tachycardia. The V2 agonists SKF 101926, SKF 104146 and SKF 104244 did not stimulate clotting factor release, blood pressure, heart rate or plasma renin activity in this species at the doses tested. Thus, the rhesus monkey is a nonhuman primate species in which dDAVP stimulation of FVIIIc and vWF occurs. The results support the hypothesis that dDAVP stimulation of clotting factor release is mediated by a low-affinity, V2-like receptor mechanism. The tachycardia and renin release associated with dDAVP administration are most likely secondary to vasodilation, also mediated by a V2-like mechanism.