Potentiation of infectivity and pathogenesis of influenza a virus by a house dust mite protease

Common house dust mites (e.g., Dermatophagoides farinae) excrete a serine-type (Df) protease. Dfprotease obtained from cultured mites enhanced viral replication in vitro via proteolytic cleavage of viral hemagglutinin (HA) into HAl and HA2, which confers potent viral infectivity. Its potency is 2- to 5-fold higher than bovine trypsin or human plasmin. Df protease also markedly accelerated virus propagation in vivo: A minute quantity of protease (estimated delivered amount, 0.8-3.2 μg) produced ∼4- to 100-fold increases in infectious virus in the mouse lung. Similar augmentation of viral replication by Df protease was observed in ferret models of nasopharyngeal infections of influenza virus. All extracts from ordinary house dust contained a serine-type protease that cleaved HA into HAl and HA2. Thus, mite protease in house dust may enhance the pathogenesis of influenza virus.