Induction of anti-CD8 resistant cytotoxic T lymphocytes by anti-CD8 antibodies. Functional evidence for T cell signaling induced by multi-valent cross-linking of CD8 on precursor cells

The effector function of most MHC class I allospecific CTL is inhibited by anti-CD8 mAb. In the present study, we report the surprising observation that multi-valent cross-linking of CD8 molecules on precursor cells by specific antibody actively induces the generation of CD8+ class I allospecific CTL whose lytic function is resistant to anti-CD8 antibody inhibition, and actively induces down-modulation of cell surface CD8 expression on these cells. In marked contrast, bi-valent cross-linking of CD8 inhibits the generation of CD8+ CTL from precursor cells and fails to induce down-modulation of cell surface CD8 expression. These results demonstrate that CD8 can transduce net positive signals, but only when the molecule is extensively cross-linked.     

Bone graft survival in expanded skin

The effect of tissue expansion on iliac bone graft (onlay) survival was studied on the skulls of 35 New Zealand white rabbits. Wet bone weights at the time of grafting and at sacrifice in control animals (group I) were compared to three experimental groups. Histologic sections of the developing and resolving pseudosheath and skin envelope were performed. A self-inflating 5-mil-thick silicone expander was used for soft-tissue expansion over the rabbit snout. Bone grafts were subsequently placed in this site. Elliptical snout excision without expansion (group II) demonstrated no statistically significant difference in bone graft survival when compared to controls (group I) (p = 0.350). Full tissue expansion followed by immediate bone grafting (group III) within the pseudosheath cavity likewise demonstrated no statistically significant difference in bone graft survival when compared to controls (group I) (p = 0.500); however, when full tissue expansion was followed by delayed (2 weeks) bone grafting to allow for resolution of the giant cell inflammatory reaction of the pseudosheath (group IV), a statistically significant increased bone graft survival was achieved (p less than 0.001). The study demonstrates that the increased vascularity in the pseudosheath and in the expanded soft-tissue envelope significantly increased bone graft survival only when bone grafting was delayed.     

Nonequivalent effects of PKC activation by PMA on murine CD4 and CD8 cell-surface expression

The membrane glycoproteins CD4 (L3T4) and CD8 (Lyt2) are expressed on distinct populations of mature murine T lymphocytes, and are thought to be receptors for monomorphic determinants expressed on MHC class II and class I molecules, respectively. Although they differ in their ligand specificity, it has been presumed that CD4 and CD8 perform equivalent functions in the T cells that bear them. Since activation of protein kinase C (PKC) is known to cause rapid down-regulation of various receptors, including the T cell receptor complex (TcR complex), we treated cells with phorbol 12-myristate 13-acetate (PMA), a PKC activator, to determine whether cell-surface expression of CD4 and CD8 would be similarly affected by this intracellular mediator. Brief or relatively prolonged treatment with PMA induced mature murine T cells to reduce their surface expression of the TcR complex and of CD4, but not of CD8. Similarly, PMA rapidly induced transfected L cells to down-regulate surface CD4 expression, but had no effect on surface CD8 expression. Most significantly, PMA treatment induced CD4+CD8+ immature thymocytes to rapidly reduce their surface CD4 expression, but, again, it had no immediate effect on the surface expression of CD8. These results indicate that CD4 and TcR complex cell-surface expression are both sensitive to PKC activation by brief treatment with PMA, whereas CD8 expression is not, and suggest that CD4 and CD8 surface expression levels are regulated by distinct intracellular mechanisms.     

Studies on the immediate and delayed leucocytosis elicited by brief (30-min) strenuous exercise

Eight healthy male volunteers exercised for two 30-min sessions starting 3 h apart on an electronically braked cycle ergometer at a work load (mean 155.9 W, SD 33.4 W) which required an oxygen consumption that was 70% of their maximal rate of oxygen uptake. Venous blood samples were taken through an indwelling cannula over a period of 6 h beginning shortly before the first bout of exercise and were analysed for routine haematological parameters and for lactate, noradrenaline, adrenaline and cortisol. Both bouts of exercise induced an immediate leucocytosis due to rises in lymphocytes and neutrophils but only the first exercise bout induced a substantial delayed neutrophilia. In at least five subjects, changes in lymphocyte and platelet numbers were correlated (Spearman's rank procedure, P less than 0.05) with simultaneous changes in the plasma concentrations of lactate, noradrenaline and adrenaline over the 6-h period studied. Increases in the plasma concentration of cortisol due to exercise correlated positively with the percentage changes in neutrophil numbers at 3 h and 6 h. These results are consistent with the suggestion that the immediate and delayed leucocytosis induced by exercise are mediated respectively by catecholamine and by cortisol.     

Effect of light and nutrients on biomass allocation in Calamagrostis canadensis

The effects of light intensity and nutrient availability on the biomass allocation of Calamagrostis canadensis were studied under both greenhouse and field conditions In the greenhouse, seedlings from forest and wetland populations were grown in sand-peat mixtures, under three light intensities and three fertilizer levels Total above and below ground growth increased with light intensity and nutrient availability, nutrient availability, however, only altered plant growth when light intensity was above moderate levels Numbers of rhizomes were greatest under low and moderate nutrient regimes but high light was also needed for maximum numbers of rhizomes In the field, tillers and rhizomes were examined under open, 40% and 85% canopy cover Tiller and rhizome weight and diameter of rhizomes decreased with canopy closure However, proportional allocation of biomass to rhizomes was greatest and percentage total non-structural carbohydrates of rhizomes was lowest under a 40% canopy     

Species-specific diversity among simian immunodeficiency viruses from African green monkeys

The prevalence, natural history, and genetic characteristics of simian immunodeficiency virus (SIV) infections in most feral African monkey species are presently unknown, yet this information is essential to elucidate their origin and relationship to other simian and human immunodeficiency viruses. In this study, a combination of classical and molecular approaches were used to identify and characterize SIV isolates from West African green monkeys (Cercopithecus sabaeus) (SIVagm isolates). Four SIVagm viruses from wild-caught West African green monkeys were isolated and analyzed biologically and molecularly. Amplification, cloning, and sequencing of a 279-bp polymerase fragment directly from uncultured peripheral blood mononuclear cells was facilitated by the use of nested polymerase chain reaction. The results indicated that West African green monkeys are naturally infected with SIVs which are closely related to East African SIVagm isolates. However, structural, antigenic, and genetic differences were observed which strongly suggest that the West African green monkey viruses comprise a phylogenetically distinct subgroup of SIVagm. These findings support our previous hypothesis that SIVagm viruses may have evolved and diverged coincident with the evolution and divergence of their African green monkey host. In addition, this study describes a polymerase chain reaction-based approach that allows the identification and molecular analysis of divergent SIV strains directly from primary monkey tissue. This approach, which does not depend on virus isolation methods, should facilitate future studies aimed at elucidating the origins and natural history of SIVs in feral African green monkey populations.     

Interaction of lymphocytes and high endothelial venules in irradiated lymph nodes

After total-body exposure to various doses of ionizing radiation, the ability of lymphocytes to interact specifically with high endothelial venules of rat cervical and mesenteric lymph nodes was analyzed in frozen sections. Following a radiation dose of 1.5 Gy, high endothelial venules remained intact and the binding of unirradiated lymphocytes to the venules was enhanced relative to unirradiated controls. At radiation doses above 5.0 Gy, damage to high endothelial venules was observed histologically as well as assessed functionally. There was a significant decrease in specific lymphocyte-venule binding and a significant increase in nonspecific binding. These findings suggest that radiation-induced damage to high endothelial venules might play a role in radiation-induced immunosuppression by interfering with the normal passage of lymphocytes from the blood into lymph nodes via a specific interaction between lymphocytes and high endothelial venules.     

Apoptosis: final control point in cell biology

The discovery of apoptosis, a widespread and morphologically distinct form of physiological cell death, has had an extraordinary impact on cell biology. The importance of apoptosis stems from its active nature and its potential for controlling biological systems. The growing appreciation of the significance of this process has stimulated intense investigation into the molecular mechanisms involved and into its fundamental implications for developmental biology, immunology and oncology.