Very little is known about the mechanism of cell entry of hepatitis A virus (HAV), and the identification of cellular receptors for this picornavirus has been elusive. Here we describe the molecular cloning of a cellular receptor for HAV using protective monoclonal antibodies raised against susceptible African green monkey kidney (AGMK) cells as probes. Monoclonal antibodies 190/4, 235/4 and 263/6, which reacted against similar epitopes, specifically protected AGMK cells against HAV infection by blocking the binding of HAV. Expression cloning and nucleotide sequence analysis of the cDNA coding for epitope 190/4 revealed a novel mucin‐like class I integral membrane glycoprotein of 451 amino acids, the HAV cellular receptor 1 (HAVcr‐1). Immunofluorescence analysis indicated that mouse Ltk‐ cells transfected with HAVcr‐1 cDNA gained limited susceptibility to HAV infection, which was blocked by treatment with monoclonal antibody 190/4. Our results demonstrate that the HAVcr‐1 polypeptide is an attachment receptor for HAV and strongly suggest that it is also a functional receptor which mediates HAV infection. This report constitutes the first identification of a cellular receptor for HAV.

Entry of Japanese encephalitis virus (JEV) into cells was analysed by using the vertebrate cell line Vero. Vero cells were treated with chlorpromazine, nystatin or cytochalasin D, which inhibit clathrin-and caveola-dependent endocytosis, and macropinocytosis of the cells, respectively. Productive JEV infection was inhibited by pretreatment with chlorpromazine; the number of JEV antigen-positive cells was less than one-fifth of that in untreated cultures, but was not significantly decreased by pretreatment with nystatin or cytochalasin. Viral antigens were detected in the membrane fractions, but not in the endosome fractions from chlorpromazine-treated JEV-inoculated cells. When the cells were treated with chlorpromazine, clathrin heavy chain antigen and JEV antigen were not detected in cytoplasm by indirect immunofluorescence staining. These results indicate that JEV is taken up by cells through the clathrin-dependent endocytic pathway, and this process leads to infection.

CD8ϩ cytotoxic T lymphocytes (CTLs) recognize virus-derived peptides in association with major histocompatibility complex class I molecules on the surface of antigen-presenting cells and kill the virus-infected target cells. There are a number of evidences showing that CTLs play a central role in the clearance of pathogenic viruses (67). In case of hepatitis C virus (HCV) infection, vigorous HCV-specific CTL responses existed in the persons resolving acute HCV infection (27). In the experimental model, chimpanzees who cleared HCV generated strong CTL but poor antibody responses, whereas other chimpanzees developing chronic hepatitis generated much weaker CTL response (12). Thus, spontaneous resolution of HCV is likely to be associated with HCV-specific CTLs rather than neutralizing antibodies (12,18,27,58). However, Ͼ60% of HCV-infected individuals turn out to have chronic hepatitis (1). Chronic HCV hepatitis eventually progresses to cirrhosis and hepatocellular carcinoma (53). In the chronic stage, HCVspecific CTLs are detectable in both peripheral blood and liver, but the precursor frequency of HCV-specific CTLs is extremely low (27,50,51). Therefore, enhancement of HCVspecific CTL induction in HCV-infected individuals should be considered to be a strategy to clear the virus. DNA vaccination has been proven to be a useful strategy for inducing both humoral and cellular immune responses (19). DNA vaccine safely mimics the effect of live, attenuated virusbased vaccine to generate a long-lasting CTL response. However, the efficiency of DNA vaccine is sometimes quite low and, therefore, several modifications have been attempted in recent years (19). Thus far, the most successful protocol of DNA immunization for CTL induction is likely to be a consecutive immunization involving priming with plasmid DNA and boosting with recombinant virus (2,24,35,43,54). The rationale behind this strategy is that DNA priming elicits low-level but persistent immunity, followed by strong boosting with virus encoding the same recombinant antigen as the DNA encodes. This regimen of the consecutive immunization has been proven to be efficient for CTL induction by many groups (2,24,35,37,43,54). Recently, McConkey et al. (37) have shown that the prime-boost immunization induced high frequencies of antigen-specific T-cell responses to malaria antigen and displayed partial protection in humans.Interleukin-12 (IL-12) is a heterodimeric proinflammatory cytokine formed by a 35-kDa light chain (p35) and a 40-kDa heavy chain (p40) (57). This cytokine is a dominant factor in the differentiation of T helper type 1 (Th1) cells and plays an essential role in a link between innate and adaptive immunities (60). Recently, two novel polypeptides, p19 (42) and p28 (48), have been identified by searching the databases with a computationally derived profile of IL-6. These factors do not show

Since the natural immune response to hepatitis C virus (HCV) is often unable to clear the infection, to enhance immunogenicity we studied substituted peptides from an HCV cytotoxic T lymphocyte (CTL) epitope (C7A2) from a conserved region of the HCV core protein (DLMGYIPLV) recognized by CTL lines from HLA-A2.1 ϩ HCV-infected patients and HLA-A2.1 transgenic mice. HLA-A2.1 binding, human and murine CTL recognition, and in vivo immunogenicity (using mice transgenic for human HLA-A2 in lieu of immunizing humans) were analyzed to define peptides with enhanced immunogenicity. Peptides substituted at position 1 showed enhanced HLA-A2 binding affinity, but paradoxically poorer immunogenicity. A peptide with Ala substituted at position 8 (8A) showed higher HLA-A2 binding affinity and CTL recognition and was a more potent in vivo immunogen in HLA-A2-transgenic mice, inducing higher CTL responses with higher avidity against native C7A2 than induced by C7A2 itself. These results suggest that peptide 8A is a more potent in vitro antigen and in vivo immunogen than C7A2 and may be useful as a vaccine component. They provide proof of principle that the strategy of epitope enhancement can enhance immunogenicity of a CTL epitope recognized by human CTL. ( J. Clin. Invest.

Two types of light-emitting electrochemical cells (LECs) are commonly distinguished, the polymer-based LEC (p-LEC) and the ionic transition metal complex-based LEC (iTMC-LEC). Apart from marked differences in the active layer constituents, these LEC types typically show operational time scales that can differ by many orders of magnitude at room temperature. Here, we demonstrate that despite these differences p-LECs and iTMC-LECs show current, light output, and efficacy transients that follow a universal shape. Moreover, we conclude that the turn-on time of both LEC types is dominated by the ion conductivity because the turn-on time exhibits the same activation energy as the ion conductivity in the off-state. These results demonstrate that both types of LECs are really two extremes of one class of electroluminescent devices. They also implicate that no fundamental difference exists between charge transport in small molecular weight or polymeric mixed ionic and electronic conductive materials. Additionally, it follows that the ionic conductivity is responsible for the dynamic properties of devices and systems using them. This likely extends to mixed ionic and electronic conductive materials used in organic solar cells and in a variety of biological systems.