Why does the influenza virus specifically infect cells of respiratory tract?

The influenza virus has a strong preference for infecting cells of the respiratory tract due to several factors:

Receptor Specificity: The influenza virus's hemagglutinin (HA) protein binds to specific receptors on the surface of respiratory tract cells. These receptors are sialic acids, which are abundant in the respiratory tract, particularly in the nose, throat, and lungs. The HA protein allows the virus to attach to and enter these cells, initiating infection.

Cellular Environment: The respiratory tract provides a favorable environment for the influenza virus to replicate and spread. The cells in this region have the necessary machinery to support viral replication, including the presence of enzymes and other factors required for viral transcription and translation.

Temperature: The temperature of the respiratory tract is ideal for the virus's replication. The slightly cooler temperature in the nose compared to the rest of the body is optimal for the influenza virus to initiate infection.

Mucociliary Clearance: The respiratory tract is constantly exposed to various pathogens and particles from the environment. To defend against these foreign substances, the respiratory system has a self-defense mechanism called mucociliary clearance. This process involves the movement of mucus and cilia, which helps to trap and remove foreign particles from the airways. However, the influenza virus has evolved mechanisms to evade mucociliary clearance and establish successful infection within the respiratory tract.

Host Immune Response: The respiratory tract is constantly exposed to pathogens, leading to frequent immune responses. The influenza virus has developed mechanisms to evade or suppress the host immune response, allowing it to persist and replicate within the respiratory tract.

Overall, the structural features of the influenza virus, the favorable environment of the respiratory tract, and the virus's ability to evade the host immune response contribute to its specific infection of respiratory tract cells.