Recombinant subtype A and B human respiratory syncytial virus clinical isolates co-infect the respiratory tract of cotton rats.

Human respiratory syncytial virus (HRSV) is an important respiratory pathogen causing a spectrum of illness, from common cold-like symptoms, to bronchiolitis and pneumonia requiring hospitalization in infants, the immunocompromised and the elderly. HRSV exists as two antigenic subtypes, A and B, which typically cycle biannually in separate seasons. There are many unresolved questions in HRSV biology regarding the interactions and interplay of the two subtypes. Therefore, we generated a reverse genetics system for a subtype A HRSV from the 2011 season (A11) to complement our existing subtype B reverse genetics system. We obtained the sequence (HRSVA11) directly from an unpassaged clinical sample and generated the recombinant (r) HRSVA11. A version of the virus expressing enhanced green fluorescent protein (EGFP) from an additional transcription unit in the fifth (5) position of the genome, rHRSVA11EGFP(5), was also generated. rHRSVA11 and rHRSVA11EGFP(5) grew comparably in cell culture. To facilitate animal co-infection studies, we derivatized our subtype B clinical isolate using reverse genetics toexpress the red fluorescent protein (dTom)-expressing rHRSVB05dTom(5). These viruses were then used to study simultaneous in vivo co-infection of the respiratory tract. Following intranasal infection, both rHRSVA11EGFP(5) and rHRSVB05dTom(5) infected cotton rats targeting the same cell populations and demonstrating that co-infection occurs in vivo. The implications of this finding on viral evolution are important since it shows that inter-subtype cooperativity and/or competition is feasible in vivo during the natural course of the infection.

Measles virus infection of epithelial cells in the macaque upper respiratory tract is mediated by subepithelial immune cells.

Measles virus (MV), one of the most contagious viruses infecting humans, causes a systemic infection leading to fever, immune suppression, and a characteristic maculopapular rash. However, the specific mechanism or mechanisms responsible for the spread of MV into the respiratory epithelium in the late stages of the disease are unknown. Here we show the crucial role of PVRL4 in mediating the spread of MV from immune to epithelial cells by generating a PVRL4 "blind" recombinant wild-type MV and developing a novel in vitro coculture model of B cells with primary differentiated normal human bronchial epithelial cells. We utilized the macaque model of measles to analyze virus distribution in the respiratory tract prior to and at the peak of MV replication. Expression of PVRL4 was widespread in both the lower and upper respiratory tract (URT) of macaques, indicating MV transmission can be facilitated by more than only epithelial cells of the trachea. Analysis of tissues collected at early time points after experimental MV infection demonstrated the presence of MV-infected lymphoid and myeloid cells contacting respiratory tract epithelium in the absence of infected epithelial cells, suggesting that these immune cells seed the infection in vivo. Thereafter, lateral cell-to-cell spread of MV led to the formation of large foci of infected cells in the trachea and high levels of MV infection in the URT, particularly in the nasal cavity. These novel findings have important implications for our understanding of the high transmissibility of measles.