Most proteins are secreted through conventional protein secretion pathway. These proteins contain signal peptides that direct their transport to the plasma membrane through the ER-Golgi pathway. In our experiments, many classically secreted proteins were detected in cell culture supernatants of macrophages in response to influenza A virus infection. In addition to classical protein secretion, activated immune cells secrete proteins lacking signal peptides through unconventional secretory pathway [47] . DAMPs are nuclear or cytosolic proteins with defined intracellular functions [48] . They are usually hidden in intact cells and released during tissue damage through unconventional protein secretion pathway. Our quantitative high-throughput secretome analysis revealed secretion of several DAMPs in response to influenza A virus infection. These included 50 kDa cleavage product of amyloid precursor protein, HMGBs, galectins, and S100 proteins. Amyloid precursor protein is processed by a-, band c-secretases to generate inflammatory amyloid b peptide [49] . Fibrillogenic amyloid b peptide 42 (Ab 42 ) is a known activator of NLRP3 inflammasome in migroglial cells [50] and it is involved in the pathogenesis of Alzheimer's disease [51] . We were not able to control siRNA and P2X 7 receptor specific siRNAs for 24 h after which the cells were left unstimulated or infected with influenza A virus for 9 h. IL-18 secretion was analyzed from cell culture supernatants with IL-18 ELISA. E. P2X 7 receptor expression was analyzed by Western blotting with anti-P2X 7 specific Abs. F. Macrophages were infected with influenza A virus for 9 h in the presence and absence of PP2 (5 mM), after which the cell culture media was collected and analyzed with IL-18 ELISA. G. Macrophages were primed with LPS for 18 h, after which the macrophages were left untreated or treated with PP2 and infected with influenza A virus for 9 h. The cell culture supernatants were analyzed with IL-1b ELISA. doi:10.1371/journal.ppat.1001340.g005 detect secretion of Ab 42 by ELISA in influenza A virus-infected macrophages (data not shown). However, the secretome data showed that amyloid precursor protein is expressed, processed, and secreted in response to influenza A virus infection. In addition, subcellular proteomics data demonstrates that nicastrin and preselinin, which are components of c-secretases are expressed in human macrophages. This finding suggests that b-amyloid protein and its processing machinery have a specific function in antiviral response.