Synapsin associates with cyclophilin B in an ATP- and cyclosporin A-dependent manner

Immunophilins are ubiquitous enzymes responsible for proline isomerisation during protein synthesis and for the chaperoning of several membrane proteins. These activities can be blocked by the immunosuppressants cyclosporin A, FK506 and rapamycin. It has been shown that all three immunosuppressants have neurotrophic activity and can modulate neurotransmitter release, but the molecular basis of these effects is currently unknown. Here, we show that synapsin I, a synaptic vesicle-associated protein, can be purified from Torpedo cholinergic synaptosomes through its affinity to cyclophilin B, an immunophilin that is particularly abundant in brain. The interaction is direct and conserved in mammals, and shows a dissociation constant of about 0.5 microM in vitro. The binding between the two proteins can be disrupted by cyclosporin A and inhibited by physiological concentrations of ATP. Furthermore, cyclophilin B co-localizes with synapsin I in rat synaptic vesicle fractions and its levels in synaptic vesicle-containing fractions are decreased in synapsin knockout mice. These results suggest that immunophilins are involved in the complex protein networks operating at the presynaptic level and implicate the interaction between cyclophilin B and synapsins in presynaptic function.     

Opposite effects of serotonin and interferon-α on the membrane potential and function of human natural killer cells

Summary In an earlier article, we reported that serotonin (5-hydroxytryptamine, 5-HT) inhibits the natural killer cell (NK) cytotoxicity of human whole blood in a dose-dependent manner and that natural human interferon-α (IFN-α) partially eliminates this effect. Because natural IFN-α might contain factors other than IFN, we repeated these experiments with recombinant human interferon-α (rhIFN-α) and separated blood lymphocytes enriched with NK cells and then demonstrated that IFN really is responsible for this effect. Furthermore, this investigation was carried out to clarify the mechanisms of the action of 5-HT and of rhIFN-α on NK cells. The inhibition of the cytotoxicity was pronounced when 5-HT was added at the onset of the cytotoxic assay, whereas the pretreatment of lymphocytes for 18 h only led to a slight inhibition. Moreover, rhIFN-α applied 1 h before or 1 h after the addition of 5-HT decreased the inhibitory effect of 5-HT. Flow cytometric analysis involving the use of a voltage-sensitive dye, oxonol, revealed that 5-HT depolarized, whereas rhIFN-α hyperpolarized the plasma membrane of the lymphocytes. Thus, it seems likely that the inhibitory effect of 5-HT on the cytotoxicity of peripheral human lymphocytes is due to the depolarization on the plasma membrane of the effector cells and that rhIFN-α antagonizes this ability via its hyperpolarizing activity.     

Smallpox vaccine-induced antibodies are necessary and sufficient for protection against monkeypox virus

Vaccination with live vaccinia virus affords long-lasting protection against variola virus, the agent of smallpox. Its mode of protection in humans, however, has not been clearly defined. Here we report that vaccinia-specific B-cell responses are essential for protection of macaques from monkeypox virus, a variola virus ortholog. Antibody-mediated depletion of B cells, but not CD4+ or CD8+ T cells, abrogated vaccine-induced protection from a lethal intravenous challenge with monkeypox virus. In addition, passive transfer of human vaccinia-neutralizing antibodies protected nonimmunized macaques from severe disease. Thus, vaccines able to induce long-lasting protective antibody responses may constitute realistic alternatives to the currently available smallpox vaccine (Dryvax).     

Distinct functions of DC-SIGN and its homologues L-SIGN (DC-SIGNR) and mSIGNR1 in pathogen recognition and immune regulation

Antigen presenting cells express C-type lectins that are involved in pathogen capture, processing and antigen presentation to induce immune responses against these pathogens. However, it is becoming clear that pathogens have evolved to subvert the function of some C-type lectins to escape immune surveillance. An important C-type lectin family is represented by DC-SIGN and its homologues in human and mouse. Here we discuss the structure in relation to the pathogen binding specificity of the SIGN receptors and the function of these receptors in mouse and humans.     

Human neutrophils kill Bacillus anthracis

Bacillus anthracis spores cause natural infections and are used as biological weapons. Inhalation infection with B. anthracis, the etiological agent of anthrax, is almost always lethal, yet cutaneous infections usually remain localized and resolve spontaneously. Neutrophils are typically recruited to cutaneous but seldom to other forms of anthrax infections, raising the possibility that neutrophils kill B. anthracis. In this study we infected human neutrophils with either spores or vegetative bacteria of a wild-type strain, or strains, expressing only one of the two major virulence factors. The human neutrophils engulfed B. anthracis spores, which germinated intracellularly and were then efficiently killed. Interestingly, neutrophil killing was independent of reactive oxygen species production. We fractionated a human neutrophil granule extract by high-performance liquid chromatography and identified alpha-defensins as the component responsible for B. anthracis killing. These data suggest that the timely recruitment of neutrophils can control cutaneous infections and possibly other forms of B. anthracis infections, and that alpha-defensins play an important role in the potent anti-B. anthracis activity of neutrophils.     

Silent antibodies

Over the past years, progress has been made in understanding B cells and antibody recognition functions, particularly in the context of autoimmune diseases. In addition to the existence of "natural antibodies", recent studies suggest the existence of immunoglobulins with no apparent specificity that may acquire polyreactivity following a mild denaturation in inflammatory sites. They are called "silent antibodies". Together with related observations on B cell development, selection and signaling, the recent insights are providing clues into our understanding of autoimmunity.     

Seasonal environmental changes regulate the expression of the histone variant macroH2A in an eurythermal fish

Adaptation to cold and warm conditions requires dramatic change in gene expression. The acclimatization process of the common carp Cyprinus carpio L. in its natural habitat has been used to study how organisms respond to natural environmental changes. At the cellular level, adaptation to cold condition is accompanied by a dramatic alteration in nucleolar structure and a down regulation of the expression of ribosomal genes. We show that the enrichment of condensed chromatin in winter adapted cells is not correlated with an increase of the heterochromatin marker trimethyl and monomethyl K20H4. However, the expression of the tri methyl K4 H3 and of the variant histone macroH2A is significantly increased during the winter season together with a hypermethylation of CpG residues. Taking into account the properties of macroH2A toward chromatin structure and dynamics and its role in gene repression our data suggest that the increased expression of macroH2A and the hypermethylation of DNA which occurs upon winter-acclimatization plays a major role for the reorganization of chromatin structure and the regulation of gene expression during the physiological adaptation to a colder environment.     

Contrasting effects of low-dose IL-2 on vaccine-boosted simian immunodeficiency virus (SIV)-specific CD4+ and CD8+ T cells in macaques chronically infected with SIVmac251

IL-2, the first cytokine discovered with T cell growth factor activity, is now known to have pleiotropic effects on T cells. For example, it can promote growth, survival, and differentiation of Ag-selected cells, or facilitate Ag-induced cell death of T cells when Ag persists, and in vivo, it is thought to contribute to the regulation of the size of adaptive T cell response. IL-2 is deficient in HIV-1 infection and has been used in the management of HIV-1-infected individuals undergoing antiretroviral therapy. In this study, we investigated how continuous low-dose IL-2 affected the CD4+ and CD8+ T cell response induced by two inoculations of a canarypox recombinant SIV-based vaccine candidate in healthy macaques chronically infected with SIVmac251. These macaques had normal levels of CD4+ T cells at the beginning of antiretroviral therapy treatment. Vaccination in the presence of IL-2 significantly augmented Gag-specific CD8+ T cell responses, but actually reduced Gag-specific CD4+ T cell responses. Although IL-2 at low doses did not change the overall concentration of circulating CD4+ or CD8+ T cells, it expanded the frequency of CD4+CD25+ T cells. Depletion of the CD4+CD25+ T cells in vitro, however, did not result in a reconstitution of Gag-specific CD4+ responses or augmentation of SIV-specific CD8+ T cell responses. Thus, we conclude that the decrease in virus-specific CD4+ T cell response may be due to IL-2-promoted redistribution of cells from the circulation, or due to Ag-induced cell death, rather than suppression by a T regulatory population.