In the investigators' previous retrospective study, the investigators found that there were some obviously imbalanced immune responses in IPF patients, including increased cluster of differentiation 4 (CD4) T cell population, immunoglobulin and complements. The investigators also found highly expressed inflammatory cytokines (IL-17, MIG and IL-9) and high detection rates of pathogens in AE-IPF patients, especially serum immunoglobulin M (IgM) antibody of some respiratory virus. These findings provide a strong suggestion that there are some imbalance of immunologic function in IPF and there are relationship between AE-IPF and infection, especially "Cold" virus infection might be a key trigger for AE-IPF.