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.

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.

In vitro and in vivo characterization of new swine-origin H1N1 influenza viruses

Influenza A viruses cause recurrent outbreaks of local or global scale with potentially severe consequences for human health and the global economy. Recently, a new strain of influenza A virus was detected that causes disease in and transmits among humans, probably owing to little or no pre-existing immunity to the new strain. On June 11, 2009, the WHO declared that the infections caused by the new strain had reached pandemic proportion. Characterized as an influenza A virus of the H1N1 subtype, the genomic segments of the new strain were most closely related to swine viruses1. Most human infections with swine-origin H1N1 influenza viruses (S-OIVs) appear to be mild; however, more than 50% of hospitalized individuals do not have underlying health issues, attesting to the pathogenic potential of S-OIVs. To better assess the risk posed by the new virus, we characterized one of the first US S-OIV isolates, A/California/04/09 (H1N1; CA04), as well as several other S-OIV isolates, in vitro and in vivo. In mice and ferrets, CA04 and other S-OIV isolates tested replicate more efficiently than a currently circulating human H1N1 virus. In addition, CA04 replicates efficiently in nonhuman primates, causes more severe pathologic lesions in the lungs of infected mice, ferrets, and nonhuman primates than a currently circulating human H1N1 virus, and transmits among ferrets. In specific-pathogen free miniature pigs, CA04 replicates without clinical symptoms. The assessment of human sera from different age groups suggests that infection with human H1N1 viruses antigenically closely related to viruses circulating in 1918 confers neutralizing antibody activity to CA04. Finally, we show that CA04 is sensitive to approved and experimental antiviral drugs, suggesting these compounds as a first line of defence against the recently declared S-OIV pandemic.

Basal cells of differentiated bronchial epithelium are more susceptible to rhinovirus infection

We used an in vitro model of differentiated tracheobronchial epithelium to analyze the susceptibility of different cell types to infection with rhinoviruses (RVs). Primary cells from control subjects were cultured in an air-liquid interface to form differentiated epithelia. Suprabasal and basal fractions were separated after trypsin digestion, and cell suspensions were infected with serotypes RV16 and RV1A. These cell fractions were analyzed for expression of viral capsid protein VP2 (flow cytometry), viral replication (real-time PCR), cytokeratin-14, and intercellular adhesion molecule-1 (ICAM-1). Compared with suprabasal fraction, basal cells had increased percentages of cells staining positive for VP2 (RV1A: 37.8% versus 9.1%, P < 0.01; RV16: 12.0 versus 3.0%, P < 0.05). The average number of viral RNA copies per cell was also higher in basal cells (2.2- and 2.4-fold increase in RV1A- and RV16-infected cells, respectively) compared with suprabasal cells. Furthermore, ICAM-1 was expressed by 33.3% of basal cells, compared with 8.1% of suprabasal cells (P < 0.05). Finally, in culture models of epithelial injury (detached suprabasal cells or scratched surface), there was significantly greater replication of RV1A compared with intact cell layer. These findings demonstrate that basal cells are more susceptible to RV infection than suprabasal cells. For major group RV, this may be in part due to increased expression of ICAM-1; however, minor group RV also replicated more effectively in basal cells. These results suggest the possibility that epithelial cell differentiation is associated with the maturation of antiviral defense mechanisms.

Allele-specific targeting of microRNAs to HLA-G and risk of asthma

HLA-G is a nonclassic, class I HLA molecule that has important immunomodulatory properties. Previously, we identified HLA-G as an asthma-susceptibility gene and discovered that the risk of asthma in a child was determined by both the child's HLA-G genotype and the mother's affection status. Here we report a SNP in the 3' untranslated region of HLA-G that influences the targeting of three microRNAs (miRNAs) to this gene, and we suggest that allele-specific targeting of these miRNAs accounts, at least in part, for our earlier observations on HLA-G and the risk of asthma.

Allele-specific targeting of microRNAs to HLA-G and risk of asthma

HLA-G is a nonclassic, class I HLA molecule that has important immunomodulatory properties. Previously, we identified HLA-G as an asthma-susceptibility gene and discovered that the risk of asthma in a child was determined by both the child's HLA-G genotype and the mother's affection status. Here we report a SNP in the 3' untranslated region of HLA-G that influences the targeting of three microRNAs (miRNAs) to this gene, and we suggest that allele-specific targeting of these miRNAs accounts, at least in part, for our earlier observations on HLA-G and the risk of asthma.

Serum and low-density lipoprotein enhance interleukin-8 secretion by airway epithelial cells

Viral respiratory infections rapidly increase vascular permeability, which leads to the transudation of serum proteins into airway secretions and tissues. To determine whether this process activates airway epithelial cells, bronchial epithelial cells were incubated with serum, and interleukin (IL)-8 secretion and gene expression were examined. As little as 0.1% serum significantly enhanced IL-8 secretion, and maximal secretion (65 +/- 4 ng/ml, 48 h) was observed with 10% serum. Low-density lipoprotein, but not albumin or immunoglobulin G, augmented bronchial epithelial IL-8 secretion, which was partially blocked by a monoclonal antibody specific for the low-density lipoprotein receptor. The IL-8-inducing activity of plasma was also augmented by clotting and platelet activation. Mechanistically, serum activated nuclear factor-kappaB and increased the stability and steady state levels of IL-8 mRNA. In summary, specific components of serum are potent activators of IL-8 mRNA and secretion, and the increased IL-8 production is likely to be a result of both increased transcription and mRNA stability. This effect may represent an innate mechanism for the recruitment of neutrophils to the airway in response to noxious stimuli, such as viral infections, that increase vascular permeability.

Similar frequency of rhinovirus-infectible cells in upper and lower airway epithelium

Rhinovirus (RV) infections can alter lower airway physiology and inflammation, yet the characteristics of RV replication in lower airway cells are incompletely understood. An RV serotype 16 (RV16)-specific monoclonal antibody was identified. Immunohistochemistry and an infectious center assay were used to quantitate the infectivity of RV16 in primary bronchial and adenoidal epithelial cells. The proportion of infectible epithelial cells increased with the inoculum but did not exceed 10%. Analysis of bronchial tissue samples infected ex vivo demonstrated a small subset of RV-infected cells in the epithelial layer. These data confirm previous reports that RV infects only a small subset of epithelial cells in upper airway tissues and indicate that lower airway epithelial cells have a similar susceptibility to RV infection. In confirming that RV can infect cells in the lower airway, these results suggest that lower airway dysfunction occurs through this mechanism in susceptible persons.