Rapid identification and quantitation of cells infected by recombinant herpesvirus (pseudorabies virus) using a fluorescence-based beta-galactosidase assay and flow cytometry

Brain control of humoral immune responses amenable to behavioural modulation

It has been speculated that brain activities might directly control adaptive immune responses in lymphoid organs, although there is little evidence for this. Here we show that splenic denervation in mice specifically compromises the formation of plasma cells during a T cell-dependent but not T cell-independent immune response. Splenic nerve activity enhances plasma cell production in a manner that requires B-cell responsiveness to acetylcholine mediated by the α9 nicotinic receptor, and T cells that express choline acetyl transferase^1,2 probably act as a relay between the noradrenergic nerve and acetylcholine-responding B cells. We show that neurons in the central nucleus of the amygdala (CeA) and the paraventricular nucleus (PVN) that express corticotropin-releasing hormone (CRH) are connected to the splenic nerve; ablation or pharmacogenetic inhibition of these neurons reduces plasma cell formation, whereas pharmacogenetic activation of these neurons increases plasma cell abundance after immunization. In a newly developed behaviour regimen, mice are made to stand on an elevated platform, leading to activation of CeA and PVN CRH neurons and increased plasma cell formation. In immunized mice, the elevated platform regimen induces an increase in antigen-specific IgG antibodies in a manner that depends on CRH neurons in the CeA and PVN, an intact splenic nerve, and B cell expression of the α9 acetylcholine receptor. By identifying a specific brain-spleen neural connection that autonomically enhances humoral responses and demonstrating immune stimulation by a bodily behaviour, our study reveals brain control of adaptive immunity and suggests the possibility to enhance immunocompetency by behavioural intervention.

Improved retroviral suicide gene transfer in colon cancer cell lines after cell synchronization with methotrexate

Background

Cancer gene therapy by retroviral vectors is mainly limited by the level of transduction. Retroviral gene transfer requires target cell division. Cell synchronization, obtained by drugs inducing a reversible inhibition of DNA synthesis, could therefore be proposed to precondition target cells to retroviral gene transfer. We tested whether drug-mediated cell synchronization could enhance the transfer efficiency of a retroviral-mediated gene encoding herpes simplex virus thymidine kinase (HSV-tk) in two colon cancer cell lines, DHDK12 and HT29.

Methods

Synchronization was induced by methotrexate (MTX), aracytin (ara-C) or aphidicolin. Gene transfer efficiency was assessed by the level of HSV-TK expression. Transduced cells were driven by ganciclovir (GCV) towards apoptosis that was assessed using annexin V labeling by quantitative flow cytometry.

Results

DHDK12 and HT29 cells were synchronized in S phase with MTX but not ara-C or aphidicolin. In synchronized DHDK12 and HT29 cells, the HSV-TK transduction rates were 2 and 1.5-fold higher than those obtained in control cells, respectively. Furthermore, the rate of apoptosis was increased two-fold in MTX-treated DHDK12 cells after treatment with GCV.

Conclusions

Our findings indicate that MTX-mediated synchronization of target cells allowed a significant improvement of retroviral HSV-tk gene transfer, resulting in an increased cell apoptosis in response to GCV. Pharmacological control of cell cycle may thus be a useful strategy to optimize the efficiency of retroviral-mediated cancer gene therapy.

The porcine humoral immune response against pseudorabies virus specifically targets attachment sites on glycoprotein gC

High titers of virus-neutralizing antibodies directed against glycoprotein gC of Pseudorabies virus (PRV) (Suid herpesvirus 1) are generally observed in the serum of immunized pigs. A known function of the glycoprotein gC is to mediate attachment of PRV to target cells through distinct viral heparin-binding domains (HBDs). Therefore, it was suggested that the virus-neutralizing activity of anti-PRV sera is directed against HBDs on gC. To address this issue, sera with high virus-neutralizing activity against gC were used to characterize the anti-gC response. Epitope mapping demonstrated that amino acids of HBDs are part of an antigenic antibody binding domain which is located in the N-terminal part of gC. Binding of antibodies to this antigenic domain of gC was further shown to interfere with the viral attachment. Therefore, these results show that the viral HBDs are accessible targets for the humoral anti-PRV response even after tolerance induction against self-proteins, which utilize similar HBDs to promote host protein-protein interactions. The findings indicate that the host's immune system can specifically block the attachment function of PRV gC. Since HBDs promote the attachment of a number of herpesviruses, the design of future antiherpesvirus vaccines should aim to induce a humoral immune response that prevents HBD-mediated viral attachment.

A flow cytometric method for the rapid detection of beta-galactosidase transfected cells: an in vitro and in vivo study

A flow cytometric method has been developed for the rapid analysis of lacZ transduced cells. The method described is based on an indirect immunofluorescence staining procedure using a monoclonal antibody which binds specifically to beta-galactosidase from E. coli and to beta-galactosidase fusion proteins. This technique was used for the quantification in vitro as well as in vivo of beta-galactosidase expression in B16 melanoma cells. The described method is appropriate for a variety of cell types (species, lineage), is simple, quantitative, reliable, rapid and applicable to all constructs containing the lacZ selectable markers. It should prove to be very helpful (1) for the quantification of cells expressing the lacZ reporter gene and (2) for studying gene regulation, including transfection modality, promoter efficacy, enhancer activity, and other regulatory factors.

Cell surface proteoglycans are not essential for infection by pseudorabies virus

Cell surface proteoglycans, in particular those carrying heparan sulfate glycosaminoglycans, play a major role in primary attachment of herpesviruses to target cells. In pseudorabies virus (PrV), glycoprotein gC has been shown to represent the major heparan sulfate-binding virion envelope protein (T. C. Mettenleiter, L. Zsak, F. Zuckermann, N. Sugg, H. Kern, and T. Ben-Porat, J. Virol. 64:278-286, 1990). Since PrV gC is nonessential for viral infectivity in vitro and in vivo, either the interaction between virion envelope and cellular heparan sulfate is not necessary to mediate infection or other virion envelope proteins can substitute as heparan sulfate-binding components in the absence of gC. To answer these questions, we analyzed the infectivity of isogenic gC+ and gC- PrV on mouse L-cell derivatives with defects in glycosaminoglycan biosynthesis, using a rapid and sensitive fluorescence-based beta-galactosidase assay and single-cell counting in a fluorescence-activated cell sorter. Our data show that (i) in the virion, glycoprotein gC represents the only proteoglycan-binding envelope protein, and (ii) cellular proteoglycans are not essential for infectivity of PrV. Attachment studies using radiolabeled virions lacking either gC or the essential gD confirmed these results and demonstrated that PrV gD mainly contributes to binding of Pr virions to cell surface components other than proteoglycans. These data demonstrate the presence of a proteoglycan-independent mode of attachment for Pr virions leading to infectious entry into target cells.