No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

The constant battle between pathogen and host has led to substantial diversity and adaptability of the host immune system. Pathogens too, have evolved unique mechanisms to evade their hosts. The production of superantigens is one of these mechanisms. Superantigens are potent T cell mitogens that have the unique ability to bind simultaneously to major histocompatibility complex (MHC) class II molecules and T cell receptors (TCRs). The resulting uncontrolled activation of up to 20% of all T cells and the subsequent cytokine release, can lead to fever, shock and death. Superantigens are not processed intracellularly like conventional antigens but instead bind as intact proteins to MHC class II molecules expressed on the surface of professional antigen presenting cells. On the hypothesis that the unique properties of superantigens may serve useful for vaccine delivery, several bacterial superantigens were selectively mutated at their TCR-binding site with the ultimate goal of creating a safe, non-toxic carrier protein that could target antigen presenting cells by binding to MHC class II. Antigen presenting cells that expressed MHC class II were indeed targeted by the TCR-binding-deficient superantigens. Cellular internalisation of the superantigen into vesicles was observed as early as 30 min. These supcrantigens were also shown to traffic to, and be captured by, the lymph nodes of immunised mice. Using TCR-binding-deficicnt superantigens as vaccine carrier proteins, enhanced antigenicity and immunogenicity of the conjugated MHC class I-restricted peptide antigen. GP33, was observed in a mouse model. In vitro studies revealed up to 200-fold enhancement of antigenicity when GP33 was conjugated to superantigen. Enhanced immunogenicity was also observed in vivo, with conjugates providing protection against Lymphocytic choriomeningitis virus infection after only a single immunisation. These results indicate that modified superantigens are able to safely deliver peptides for cross-presentation, and may serve as a novel mechanism for vaccine delivery.

The temporal and spatial relationships between altered vascular function and cardiac muscle cell injury at the margins of developing myocardial infarcts were investigated, because such knowledge might provide potential for intervention in the evolution of myocardial infarcts and limitation of their size. Regional myocardial ischaemia was modelled in isolated rabbit hearts subjected to ligation of the ventral interventricular branch of the left coronary artery (0,30,60,120 or 240 minutes duration), the remainder of the heart being continuously perfused with oxygenated Krebs-Henseleit buffer solution. After the experimental ischaemic period, the whole heart was fixed by perfusion with phosphate-buffered 2.5% glutaraldehyde which, in preliminary studies, was shown not only to preserve the morphological appearance of cardiac muscle cells, but also to stabilise the distribution of flow through the myocardial blood vessels in the pattern pertaining immediately prior to fixation. Polymerising acrylic resin (L.R. White) was then injected into the vessels of the ischaemic and non-ischaemic regions simultaneously at identical pressures. Resin injected into the ischaemic region contained lead dioxide whilst that injected into the other vessels contained Fat Red 7B dye to allow identification of the source of supply of blood vessels within the heart. Cryofracture, freeze-drying and imaging by scanning electron microscopy (SEM) with a backscattered electron detector and low vacuum specimen chamber conditions were used. This made possible examination of transmural segments of myocardium spanning the margins of the ischaemic and control ventricular myocardium containing blood vessels filled by resin. SEM showed severe injury of cardiac muscle cells after 60 minutes of ischaemia, as characterised by separation and swelling of some organelles. Earlier ischaemic changes in some cells (focal increase in prominence of t-tubules and sarcoplasmic reticulum) were seen after 30 minutes. There was a transmural progression in development of irreversible injury from the subendocardium to the epicardium between 60 and 120 minutes corresponding to the "wavefront phenonenon". The lateral margins did not show such marked progression and were typically sharply demarcated on a cell-to-cell basis after 60 minutes. An increase in the proportion of functional capillary pathways (from 55% to 85%) in early (30 minutes) ischaemia was succeeded by a profound perfusion defect, corresponding to the "no-reflow" phenomenon, which had a very close temporal and spatial association with severe injury of cardiac muscle cells. Loss of patency was associated with increased proportions of collapsed, compressed capillaries and swollen myocardial cells. This study demonstrated that there is a significant region of myocardium which for a period shows intermediate degrees of myocyte injury (and is thus potentially salvageable) in the subepicardial portion of the developing infarct. Contrary to the claims of various authors similar potentially salvageable lateral "border zones" were neither large nor non-existent. Within 150 microns of the typically abrupt boundary, small discontinuous areas (<20% of this region) showed intermediate degrees of injury, and there was also an increased proportion of non-functional capillaries which were not collapsed or compressed, resulting in a 'low-flow' zone. This narrow lateral zone requires further investigation to determine whether it is static, and thus of negligible size, or whether it moves in advance of infarction and is thus pathogenetically significant.

Several studies have shown that non-cycling cells are resistant to the cytotoxic effects induced by amsacrine (m-AMSA; 4'-(9-acridinylamino)methanesulphon-m-anisidide). This resistance may limit the activity of m-AMSA and related 9-anilinoacridine antitumour agents against solid tumours. The biochemical mechanism(s) for this resistance have been investigated using spontaneously transformed Chinese hamster fibroblast (AA8 cells) in log- and plateau-phase spinner cultures. In early plateau phase most cells entered a growth-arrested state with a G1-G0 DNA content and showed a marked decrease in sensitivity to cytotoxicity after a 1-h exposure to m-AMSA or its solid tumour-active analogue, CI-921. Studies with radiolabelled m-AMSA demonstrated that changes in sensitivity to m-AMSA-induced cell killing were not due to a difference in uptake or retention of drug by log- and plateau-phase cells, and there was no significant metabolism of drug by either log- or plateau-phase cells. Thus, after a 1-h exposure to [3H]-m-AMSA at 37°C, a small proportion (1%) of cell-associated radioactivity was covalently bound to macromolecules, but most of the cell-associated radioactivity represented unchanged m-AMSA. There was no evidence for any oxidative metabolism to reactive quinoidal species in these tumour cells. However, studies with a fluorescence assay for DNA unwinding indicated that plateau-phase cells were 3 to 4 times less sensitive to m-AMSA-induced DNA breakage than log-phase cells, and changes in sensitivity to m-AMSA-induced DNA breakage correlated with changes in sensitivity to cell killing by m-AMSA as cell progressed from log to plateau phase. Further studies showed that the decrease in sensitivity to m-AMSA-induced DNA stand breakage correlated with a decrease in sensitivity to covalent DNA-protein complex formation in plateau-phase cells after m-AMSA treatment. Combined with evidence that the DNA lesions rapidly disappeared from both log- and plateau-phase cells following the removal of m-AMSA (half-time approx. 4 min), this indicated that the lesions detected by the FADU assay probably arose from the stimulation of DNA-topoisomerase II (topo II) cleavable complex formation by m-AMSA. K+/SDS precipitation assays with [32p] 3’-end-labelled pBR322 DNA indicated that nuclear extracts containing topo II activity from plateau-phase cells were 3- to 4-fold less sensitive to stimulation of DNA-topo II complex formation by m-AMSA than nuclear extracts from log-phase cells. This change in sensitivity to m-AMSA-induced DNA-topo II complex formation was therefore similar to that observed with intact cells. However, P4 unknotting assays indicated that topo II activity in nuclear extracts from plateau-phase cells was only 2-fold lower than that in nuclear extracts from log-phase cells. Resistance to treatment with m-AMSA may therefore reflect a decrease in topo II activity and/or a decrease in sensitivity of topo II enzymes to stimulation of cleavable complex formation by m-AMSA in non-cycling cells.