Double-stranded RNA (dsRNA) is a potent signal to the host immune system for the presence of an ongoing viral infection. The presence of dsRNA, intracellularly or extracellularly, leads to the induction of innate inflammatory cytokines in many cell types including epithelial cells. However, the cell surface receptor for recognition of extracellular dsRNA is not yet determined. Here, we report that extracellular dsRNA is recognized and internalized by scavenger receptor class-A (SR-A). Treatment of human epithelial cells with specific antagonists of SR-A or with an anti-SR-A antibody significantly inhibited dsRNA induction of tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, IL-8, and regulated on activation normal T-cell expressed and secreted (RANTES). Furthermore, intranasal dsRNA treatment of SR-A-deficient (SR-A(-/-)) mice showed a significant decrease in the expression of inflammatory cytokines and a corresponding decrease in the accumulation of polymorphonuclear leukocytes (PMNs) in lungs. These data provide direct evidence that SR-A is a novel cell surface receptor for dsRNA, and therefore, SR-A may play a role in antiviral immune responses.

Respiratory syncytial virus (RSV) is the major cause of bronchiolitis in infants, and a common feature of RSV infections is increased lung permeability. The accumulation of fluid in the infected lungs is caused by changes in the endothelial and epithelial membrane integrity. However, the exact mechanisms of viral-induced fluid extravasation remain unclear. Here, we report that infection of human epithelial cells with RSV results in significant epithelial membrane barrier disruption as assessed by a decrease in transepithelial electrical resistance (TEpR). This decrease in TEpR, which indicates changes in paracellular permeability, was mediated by marked cellular cytoskeletal rearrangement. Importantly, the decrease in TEpR was attenuated by using p38 MAPK inhibitors (SB-203580) but was partially affected by JNK inhibitor SP-600125. Interestingly, treatment of A549 cells with MEK1/2 inhibitor (U-0126) led to a decrease in TEpR in the absence of RSV infection. The changes in TEpR were concomitant with an increase in heat shock protein 27 (Hsp27) phosphorylation and with actin microfilament rearrangement. Thus our data suggest that p38 MAPK and Hsp27 are required for RSV induction of human epithelial membrane permeability.

Asthma is characterized as a chronic inflammatory disease associated with significant tissue remodeling. Patients with asthma are more susceptible to virus-induced exacerbation, which subsequently can lead to increased rates of hospitalization and mortality. While the most common cause of asthma-related deaths is respiratory viral infections, the underlying factors in the lung environment which render asthmatic subjects more susceptible to viral exacerbation are not yet identified. Since transforming growth factor ␤ (TGF-␤) is a critical cytokine for lung tissue remodeling and asthma phenotype, we have focused on the effects of TGF-␤ on viral replication and virus-induced inflammation. Treatment of human epithelial cells with TGF-␤ increased respiratory syncytial virus (RSV) replication by approximately fourfold. Tumor necrosis factor alpha (TNF-␣) mRNA and protein expression were also significantly increased above levels with RSV infection alone. The increase in RSV replication and TNF-␣ expression after TGF-␤ treatment was concomitant with an increase in virus-induced p38 mitogen-activated protein kinase activation. Our data reveal a novel effect for TGF-␤ on RSV replication and provide a potential mechanism for the exaggerated inflammatory response observed in asthmatic subjects during respiratory viral infections.

Summary Bone morphogenetic proteins (BMPs) have multiple roles during embryogenesis. Current data indicate that the dosage of BMPs is tightly regulated for normal development in mice. Since Bmp2 or Bmp4 homozygous mutant mice show early embryonic lethality, we generated compound heterozygous mice for Bmp2 and Bmp4 to explore the impact of lowered dosage of these BMP ligands. Genotyping pups bred between Bmp2 and Bmp4 heterozygous mice revealed that the ratio of adult compound heterozygous mice for Bmp2 and Bmp4 is much lower than expected. During embryogenesis, the compound heterozygous embryos showed several abnormalities, including defects in eye formation, body wall closure defects, and ventricular septal defects (VSD) in the heart. However, the ratio of the compound heterozygous embryos was the same as expected. Caesarean sections at E18.5 revealed that half of the compound heterozygotes died soon after birth, and the majority of the dead individuals exhibited VSD. Survivors were able to grow to adults, but their body weight was significantly lower than control littermates. They demonstrated progressive abnormalities in the heart, eventually showing a branched leaflet in atrioventricular valves. These results suggest that the dosage of both BMP2 and 4 is critical for functional heart formation during embryogenesis and after birth.