Cell Surface Heparan Sulfate Is a Receptor for Human Herpesvirus 8 and Interacts with Envelope Glycoprotein K8.1

An immunodominant envelope glycoprotein is encoded by the human herpesvirus 8 (HHV-8) (also termed Kaposi's sarcoma-associated herpesvirus) K8.1 gene. The functional role of glycoprotein K8.1 is unknown, and recognizable sequence homology to K8.1 is not detectable in the genomes of most other closely related gammaherpesviruses, such as herpesvirus saimiri or Epstein-Barr virus. In search for a possible function for K8.1, we expressed the ectodomain of K8.1 fused to the Fc part of human immunoglobulin G1 (K8.1DeltaTMFc). K8.1DeltaTMFc specifically bound to the surface of cells expressing glycosaminoglycans but not to mutant cell lines negative for the expression of heparan sulfate proteoglycans. Binding of K8.1DeltaTMFc to mammalian cells could be blocked by heparin. Interestingly, the infection of primary human endothelial cells by HHV-8 could also be blocked by similar concentrations of heparin. The specificity and affinity of these interactions were then determined by surface plasmon resonance measurements using immobilized heparin and soluble K8.1. This revealed that K8.1 binds to heparin with an affinity comparable to that of glycoproteins B and C of herpes simplex virus, which are known to be involved in target cell recognition by binding to cell surface proteoglycans, especially heparan sulfate. We conclude that cell surface glycosaminoglycans play a crucial role in HHV-8 target cell recognition and that HHV-8 envelope protein K8.1 is at least one of the proteins involved.     

TLR3 and TLR4 expression in healthy and diseased human endometrium

Background  

Toll-like receptors (TLRs) play an essential role in the innate immune system by initiating and directing immune response to pathogens. TLRs are expressed in the human endometrium and their regulation might be crucial for the pathogenesis of endometrial diseases.     

Murine Flt3 ligand expands distinct dendritic cells with both tolerogenic and immunogenic properties

Human Flt3 ligand can expand dendritic cells (DC) and enhance immunogenicity in mice. However, little is known about the effects of murine Flt3 ligand (mFlt3L) on mouse DC development and function. We constructed a vector to transiently overexpress mFlt3L in mice. After a single treatment, up to 44% of splenocytes became CD11c(+) and the total number of DC increased 100-fold. DC expansion effects lasted for >35 days. mFlt3L DC were both phenotypically and functionally distinct. They had increased expression of MHC and costimulatory molecules and expressed elevated levels of B220 and DEC205 but had minimal CD4 staining. mFlt3L DC also had a markedly altered cytokine profile, including lowered secretion of IL-6, IL-10, IFN-gamma, and TNF-alpha, but had a slightly increased capacity to stimulate T cells in vitro. However, in a variety of in vivo models, DC expanded by mFlt3L induced tolerogenic effects on T cells. Adoptive transfer of Ag-pulsed mFlt3L splenic DC to naive mice actually caused faster rates of tumor growth and induced minimal CTL compared with control DC. mFlt3L also failed to protect against tumors in which human Flt3 ligand was protective, but depletion of CD4(+) T cells restored tumor protection. Our findings 1) demonstrate that mFlt3L has distinct effects on DC development, 2) suggest an important role for mFlt3L in generating DC that have tolerogenic effects on T cells, and 3) may have application in immunotherapy in generating massive numbers of DC for an extended duration.     

Cutting edge: Toll-like receptor (TLR)2- and TLR4-mediated pathogen recognition in resistance to airborne infection with Mycobacterium tuberculosis

Innate resistance against Mycobacterium tuberculosis is thought to depend critically on engagement of pattern recognition receptors on macrophages. However, the relative contribution of these receptors for containing M. tuberculosis infection has remained unexplored in vivo. To address this issue, we infected mice defective in CD14, TLR2, or TLR4 with M. tuberculosis by aerosol. Following infection with 100 mycobacteria, either mutant strain was as resistant as congenic control mice. Granuloma formation, macrophage activation, and secretion of proinflammatory cytokines in response to low-dose aerosol infection were identical in mutant and control mice. However, high-dose aerosol challenge with 2000 CFU M. tuberculosis revealed TLR2-, but not TLR4-defective mice to be more susceptible than control mice. In conclusion, while TLR2 signaling contributes to innate resistance against M. tuberculosis in borderline situations, its function, and that of CD14 and TLR4, in initiating protective responses against naturally low-dose airborne infection is redundant.     

Antibodies against Mycoplasma bovigenitalium in free-living European bison (Bison bonasus) with balanoposthitis

Since 1980 severe chronic balanoposthitis has been observed in free-living European bison (Bison bonasus) in the Bia?owieza Primeval Forest (Poland). Sera of 50 bison with balanoposthitis and 48 clinically healthy male and 49 female bison were investigated for antibodies against Mycoplasma bovis and M. bovigenitalium by western blot analysis. Prevalence of antibodies against M. bovigenitalium was significantly higher in bison with balanoposthitis than in unaffected male bison. Mycoplasma bovigenitalium may play a role in the pathogenesis of balanoposthitis in European bison.     

Optimization of dendritic cell maturation and gene transfer by recombinant adenovirus

Dendritic cells (DC) have vast potential for immunotherapy. Transferring therapeutic genes to DC may enhance their inherent T cell-stimulatory capacity. Recombinant adenovirus is the most efficient vehicle for DC gene transfer and can alone mature DC. We sought to define the parameters of adenovirus infection of murine bone marrow-derived DC (BMDC) and the concomitant impact on BMDC maturation. The efficiency of adenoviral gene transfer to DC depended on the mouse strain, the organ source of DC, and the level of DC maturation. C57BL/6 BMDC consistently had higher transgene expression than BALB/c DC. While BMDC had considerable GFP expression after AdGFP infection, adenovirus was relatively ineffective in accomplishing transgene expression in freshly isolated hepatic or splenic DC. BMDC that were relatively immature because of a shorter duration of culture had higher transgene expression after infection. Nevertheless, pretreatment of DC with exogenous stimulants such as LPS or TNF-alpha resulted in higher transgene expression. Maturation of BMDC depended only on virus entry but not viral gene or transgene expression. Therefore, DC maturation was disproportionately high compared to the percentage of DC that actually expressed the adenoviral transgene. Maturation by adenovirus was only seen in BMDC, but not in liver or splenic DC, and was more pronounced in DC from later in culture (day 12 versus day 6). There was a dose-response relationship, up to a threshold dose, between adenovirus infection and both DC maturation and enhancement of DC activation of antigen-specific T cells. Our findings underscore the importance of optimizing gene transfer to DC in designing strategies for immunotherapy.     

Molecular cloning and functional expression of zfCx52.6: a novel connexin with hemichannel-forming properties expressed in horizontal cells of the zebrafish retina

Gap junction-mediated electrical coupling contributes to synchronous oscillatory activities of neurons, and considerable progress has been made in defining the molecular composition of gap junction channels. In particular, cloning and functional expression of gap junction proteins (connexins (Cx)) from zebrafish retina have shown that this part of the brain possesses a high degree of connexin diversity that may account for differential functional properties of electrical synapses. Here, we report the cloning and functional characterization of a new connexin, designated zebrafish Cx52.6 (zfCx52.6). This connexin shows little similarity to known connexins from fish and higher vertebrates. By combining in situ hybridization with Laser Capture Microdissection and RT-PCR, we found that this novel fish connexin is expressed in horizontal cells in the inner nuclear layer of the retina. Functional expression of zfCx52.6 in neuroblastoma cells and Xenopus oocytes led to functional gap junctional channels and, in single oocytes, induced large non-junctional membrane currents indicative of the formation of hemichannels, which were inhibited in reversible fashion by raising extracellular Ca(2+) concentrations.