Cadherin-related family member 3, a childhood asthma susceptibility gene product, mediates rhinovirus C binding and replication.

Members of rhinovirus C (RV-C) species are more likely to cause wheezing illnesses and asthma exacerbations compared with other rhinoviruses. The cellular receptor for these viruses was heretofore unknown. We report here that expression of human cadherin-related family member 3 (CDHR3) enables the cells normally unsusceptible to RV-C infection to support both virus binding and replication. A coding single nucleotide polymorphism (rs6967330, C529Y) was previously linked to greater cell-surface expression of CDHR3 protein, and an increased risk of wheezing illnesses and hospitalizations for childhood asthma. Compared with wild-type CDHR3, cells transfected with the CDHR3-Y529 variant had about 10-fold increases in RV-C binding and progeny yields. We developed a transduced HeLa cell line (HeLa-E8) stably expressing CDHR3-Y529 that supports RV-C propagation in vitro. Modeling of CDHR3 structure identified potential binding sites that could impact the virus surface in regions that are highly conserved among all RV-C types. Our findings identify that the asthma susceptibility gene product CDHR3 mediates RV-C entry into host cells, and suggest that rs6967330 mutation could be a risk factor for RV-C wheezing illnesses.

Propagation of rhinovirus-C strains in human airway epithelial cells differentiated at air-liquid interface.

Rhinovirus-C (RV-C) were discovered recently using molecular methods. Classical methods failed to detect them since they could not grow in standard cell culture. The complete genome sequences of several RV-C strains are now available but there is little information about their biological characteristics. HRV-C were first grown in organ culture, and more recently, we developed a system for culturing RV-C strains in differentiated epithelial cells of human airway at air-liquid interface (ALI). These cultures supported efficient replication of RV-C strains as determined by quantitative RT-PCR. This system has enabled study of the biological characteristics of RV-C strains, including quantitative research.

Effects of rhinovirus species on viral replication and cytokine production.

BACKGROUND: Epidemiologic studies provide evidence of differential virulence of rhinovirus species (RV). We recently reported that RV-A and RV-C induced more severe illnesses than RV-B, which suggests that the biology of RV-B might be different from RV-A or RV-C. OBJECTIVE: To test the hypothesis that RV-B has lower replication and induces lesser cytokine responses than RV-A or RV-C. METHODS: We cloned full-length cDNA of RV-A16, A36, B52, B72, C2, C15, and C41 from clinical samples and grew clinical isolates of RV-A7 and RV-B6 in cultured cells. Sinus epithelial cells were differentiated at the air-liquid interface. We tested for differences in viral replication in epithelial cells after infection with purified viruses (10(8) RNA copies) and measured virus load by quantitative RT-PCR. We measured lactate dehydrogenase (LDH) concentration as a marker of cellular cytotoxicity, and cytokine and/or chemokine secretion by multiplex ELISA. RESULTS: At 24 hours after infection, the virus load of RV-B (RV-B52, RV-B72, or RV-B6) in adherent cells was lower than that of RV-A or RV-C. The growth kinetics of infection indicated that RV-B types replicate more slowly. Furthermore, RV-B released less LDH than RV-A or RV-C, and induced lower levels of cytokines and chemokines such as CXCL10, even after correction for viral replication. RV-B replicates to lower levels also in primary bronchial epithelial cells. CONCLUSIONS: Our results indicate that RV-B types have lower and slower replication, and lower cellular cytotoxicity and cytokine and/or chemokine production compared with RV-A or RV-C. These characteristics may contribute to reduced severity of illnesses that has been observed with RV-B infections.

Modeling of the human rhinovirus C capsid suggests possible causes for antiviral drug resistance.

Human rhinoviruses of the RV-C species are recently discovered pathogens with greater clinical significance than isolates in the RV-A+B species. The RV-C cannot be propagated in typical culture systems; so much of the virology is necessarily derivative, relying on comparative genomics, relative to the better studied RV-A+B. We developed a bioinformatics-based structural model for a C15 isolate. The model showed the VP1-3 capsid proteins retain their fundamental cores relative to the RV-A+B, but conserved, internal RV-C residues affect the shape and charge of the VP1 hydrophobic pocket that confers antiviral drug susceptibility. When predictions of the model were tested in organ cultures or ALI systems with recombinant C15 virus, there was a resistance to capsid-binding drugs, including pleconaril, BTA-188, WIN56291, WIN52035 and WIN52084. Unique to all RV-C, the model predicts conserved amino acids within the pocket and capsid surface pore leading to the pocket may correlate with this activity.

Biological characteristics and propagation of human rhinovirus-C in differentiated sinus epithelial cells.

Information about the basic biological properties of human rhinovirus-C (HRV-C) viruses is lacking due to difficulties with culturing these viruses. Our objective was to develop a cell culture system to grow HRV-C. Epithelial cells from human sinuses (HSEC) were differentiated at air-liquid interface (ALI). Differentiated cultures supported 1-2 logs growth of HRV-C15 as detected by quantitative RT-PCR. Two distinguishing features of HRVs are acid lability and optimal growth at 33-34 °C. We used this system to show that HRV-C15 is neutralized by low pH (4.5). In contrast to most HRV types, replication of HRV-C15 and HRV-C41 was similar at 34 and 37°C. The HSEC ALI provides a useful tool for quantitative studies of HRV-C replication. The ability of HRV-C to grow equally well at 34°C and 37°C may contribute to the propensity for HRV-C to cause lower airway illnesses in infants and children with asthma.

Protective cellular responses elicited by vaccination with influenza nucleoprotein delivered by a live recombinant attenuated Salmonella vaccine.

Orally administered recombinant attenuated Salmonella vaccines (RASVs) elicit humoral and mucosal immune responses against the immunizing antigen. The challenge in developing an effective vaccine against a virus or an intracellular bacterium delivered by RASVs is to introduce the protective antigen inside the host cell cytoplasm for presentation to MHC-I molecules for an efficient cell mediated immune response. To target the influenza nucleoprotein (NP) into the host cell cytosol, we constructed a regulated delayed lysis in vivo RASV strain χ11246(pYA4858) encoding influenza NP with a chromosomal deletion of the sifA gene to enable it to escape from the endosome prior to lysis. Oral immunization of mice with χ11246(pYA4858) (SifA⁻) with 3 booster immunizations resulted in complete protection (100%) against a lethal influenza virus (rWSN) challenge (100 LD50) compared to 25% survival of mice immunized with the isogenic χ11017(pYA4858) (SifA⁺) strain. Reducing the number of booster immunizations with χ11246(pYA4858) from 3 to 2 resulted in 66% survival of mice challenged with rWSN (100 LD50). Immunization with χ11246(pYA4858) via different routes provided protection in 80% orally, 100% intranasally and 100% intraperitoneally immunized mice against rWSN (100 LD50). A Th1 type immune response was elicited against influenza NP in all experiments. IFN-γ secreting NP147₋155 specific T cells were not found to be correlated with protection. The role of antigen-specific CD8⁺ T cells remains to be determined. To conclude, we showed that Salmonella can be designed to deliver antigen(s) to the host cell cytosol for presumably class I presentation for the induction of protective immune responses.

Delivery of woodchuck hepatitis virus-like particle presented influenza M2e by recombinant attenuated Salmonella displaying a delayed lysis phenotype.

The use of live recombinant attenuated Salmonella vaccines (RASV) is a promising approach for controlling infections by multiple pathogens. The highly conserved extracellular domain of the influenza M2 protein (M2e) has been shown to provide broad spectrum protection against multiple influenza subtypes sharing similar M2e sequences. An M2e epitope common to a number of avian influenza subtypes was inserted into the core antigen of woodchuck hepatitis virus and expressed in two different recombinant attenuated Salmonella Typhimurium strains. One strain was attenuated via deletion of the cya and crp genes. The second strain was engineered to exhibit a programmed delayed lysis phenotype. Both strains were able to produce both monomeric fusion proteins and fully assembled core particles. Mice orally immunized with the strain exhibiting delayed lysis induced significantly greater antibody titers than the Δcya Δcrp strain and provided moderate protection against weight loss to a low level challenge with the influenza strain A/WSN/33 modified to express the M2e sequence common to avian viruses. Further studies indicated that the Salmonella expressed core antigen induced comparable antibody levels to the purified core antigen injected with an alum adjuvant and that both are able to reduce viral replication in the lungs. To our knowledge this is the first report demonstrating Salmonella-mediated delivery of influenza virus M2e protein in a mammalian host to induce a protective immune response against viral challenge.

Evaluation of transmission route and replication efficiency of H9N2 avian influenza virus.

A/Chicken/Beijing/1/94 (Ck/BJ/1/94) avian influenza virus (AIV), a prototype of the H9N2 subtype, is phylogenetically similar in its hemagglutinin (HA) and neuraminidase (NA) genes to A/Chicken/Shanghai/F/98 (Ck/SH/F/98; H9N2) AIV, a natural reassortant between different sublineages. To understand the role of HA and NA genes in the airborne transmission of H9N2 AIV, we compared the transmission route and the relative replication efficiency of these strains in specific-pathogen-free chickens. Three recombinant viruses were generated by reverse genetics, containing the HA and NA genes (or both) from A/Chicken/Guangdong/SS/94 (Ck/GD/SS/94), in a background of internal genes derived from Ck/SH/F/98. Inoculated chickens were kept in either direct or indirect contact with uninoculated chickens, and viral shedding and titers were monitored. The results showed that Ck/GD/SS/94 lacks the ability to be transmitted through indirect contact, while Ck/SH/F/98 could be transmitted indirectly. Recombinant virus (RF/SSHA), containing the internal genes of Ck/SH/F/98 and the HA gene of Ck/GD/ SS/94, resulted in decreased viral titers in lung tissue as compared to the parental strain. Interestingly, substituting the NA gene, or both the NA and HA genes, of Ck/SH/F/98 with that of Ck/GD/SS/94 completely abolished the airborne transmission of the recombinant RF/SSNA and RF/SSHA/SSNA. In conclusion, Ck/SH/F/98 acquired the ability of airborne transmission and replicated with a higher efficiency in the respiratory tract of the chickens. Our data indicated that the NA gene of Ck/SH/F/98 can affect virus replication and, therefore, indirectly affect the transmission for the gene constellations of these viruses.

A one-plasmid system to generate influenza virus in cultured chicken cells for potential use in influenza vaccine.

Influenza virus has a set of ribonucleoproteins (RNPs) consisting of viral RNAs, influenza virus polymerase subunits, and nucleoprotein. Intracellular reconstitution of the whole set of RNPs via plasmid transfection results in the generation of influenza virus. By the use of reverse genetics and dual promoters, we constructed a 23.6-kb eight-unit plasmid that contains all the required constituents to generate influenza virus in chicken cells. Our "one-plasmid" system generated higher titers of influenza virus in chicken cells than the "eight-plasmid" system, enabling a simpler approach for generating vaccine seeds. Our study identified plasmid size as a potential limiting factor affecting transfection efficiency and hence the influenza viral yield from chicken cells.