Toll-like receptor 7 (TLR7) recognizes single-stranded RNA (ssRNA) viruses, such as vesicular stomatitis virus (VSV) and influenza virus. This recognition is crucial for the innate immune response, as it activates plasmacytoid dendritic cells (pDCs) and B cells, leading to the production of cytokines like IFNα. TLR7 is expressed in endosomes, where it recognizes viral RNA, and its function requires intact endocytic pathways. Mice deficient in TLR7 or its adaptor protein MyD88 showed reduced responses to VSV infection, highlighting the importance of TLR7 in viral recognition. TLR7 is distinct from TLR3 and TLR9, which recognize double-stranded RNA (dsRNA) and CpG DNA, respectively. The study also shows that endosomal acidification is essential for TLR7 activation, as inhibitors like chloroquine blocked IFNα production. In vivo, TLR7-mediated recognition of VSV is necessary for IFNα production, demonstrating the role of TLR7 in the innate immune response against ssRNA viruses. The findings suggest that TLR7 is a critical receptor for recognizing a wide range of human pathogenic viruses, and its activation is essential for effective antiviral immunity. This research provides insights into the mechanisms by which the innate immune system detects and responds to viral infections.Toll-like receptor 7 (TLR7) recognizes single-stranded RNA (ssRNA) viruses, such as vesicular stomatitis virus (VSV) and influenza virus. This recognition is crucial for the innate immune response, as it activates plasmacytoid dendritic cells (pDCs) and B cells, leading to the production of cytokines like IFNα. TLR7 is expressed in endosomes, where it recognizes viral RNA, and its function requires intact endocytic pathways. Mice deficient in TLR7 or its adaptor protein MyD88 showed reduced responses to VSV infection, highlighting the importance of TLR7 in viral recognition. TLR7 is distinct from TLR3 and TLR9, which recognize double-stranded RNA (dsRNA) and CpG DNA, respectively. The study also shows that endosomal acidification is essential for TLR7 activation, as inhibitors like chloroquine blocked IFNα production. In vivo, TLR7-mediated recognition of VSV is necessary for IFNα production, demonstrating the role of TLR7 in the innate immune response against ssRNA viruses. The findings suggest that TLR7 is a critical receptor for recognizing a wide range of human pathogenic viruses, and its activation is essential for effective antiviral immunity. This research provides insights into the mechanisms by which the innate immune system detects and responds to viral infections.