| Influenza A virus (IAV) causes respiratory tract infection in humans. IAV initiates infection in nose and spreads throughout the respiratory tract. The upper respiratory tract (URT), despite being the initial site of IAV infection, has attracted very little attention in terms of studies involving replication kinetics and associated pathology. Similarly the sinus cavity, a continuation of nasal cavity, has not been investigated, even though it potentially offers a considerable surface area for IAV replication. In this study, attempts were made to investigate IAV replication in the mouse respiratory tract including sinus cavity and also to understand the gene expression pattern of mouse β-defensin (mBD) and hydrophilic surfactant protein (SP) by Real-time PCR.;Mice were intranasally infected with either A/HK/8/68 (H3N2) or A/PR/8/34 (H1N1) strains of IAV, either at a high dose (HD) or low dose (LD). Nasal and sinus tissues were microdissected, along with trachea and lungs at various time points and used for viral titer analysis by plaque assay. The tissues from HD infection were also used for quantifying gene expression. Upon infection with HD of A/HK/8/68, the infection persisted in the URT atleast until day 7 post infection (p.i), but in lower respiratory tract (LRT) and with A/HK/8/68 LD infection, the viral titer was cleared after day 5 p.i. Whereas during both, HD and LD infection with A/PR/8/34, the viral titer persisted atleast until day 6 and day 7 respectively in all four tissues, except in lungs from HD infection, and caused more morbidity than A/HK/8/68.;Real-time PCR quantification of gene expression revealed that during A/HK/8/68 infection, mBD-1, 3, 4, SP-A and SP-D were upregulated in URT and with A/PR/8/34 infection, mBD-1 and mBD-4 were upregulated in LRT, mBD-3 was upregulated in URT. SP-D was upregulated in both URT and LRT, and SP-A was downregulated in LRT. In conclusion, replication kinetics and expression of β-defensins and surfactant proteins during A/HK/8/68 and A/PR/8/34 infection shared similarities though few differences were noted. This study also emphasizes the importance of sinus cavity in IAV infections, and the feasibility of using mice as a model for investigating IAV infections in URT and possibly for other sinus related complications. |
