Moreover, the continuing emergence of novel respiratory viruses (through antigenic recombination events and zoonosis), such as the 2009 H1N1 influenza A virus strain, highly pathogenic avian influenza viruses, SARS coronavirus and human cases of monkeypox (11, 17, 18) , taken together with the continued concern of bio-terrorism (anthrax and smallpox) (19, 20) adds to the urgent need to better understand the pathogenesis of respiratory viruses and mechanisms of protection.