Tissue kallikrein regulates alveolar macrophage apoptosis early in influenza virus infection.

Host cell proteases are involved in influenza pathogenesis. We examined the role of tissue kallikrein 1 (KLK1) by comparing wild-type (WT) and KLK1-deficient mice infected with influenza H3N2 virus. The levels of KLK1 in lung tissue and in bronchoalveolar lavage (BAL) fluid increased substantially during infection. KLK1 did not promote virus infectivity despite its trypsin-like activity, but it did decrease the initial virus load. We examined two cell types involved in the early control of pathogen infections, alveolar macrophages (AMs) and natural killer (NK) cells to learn more about the antiviral action of KLK1. Inactivating the