pDCs sense MHV via TLR7. Bone marrow–derived pDCs from TLR3^−/−, TLR7^−/−, TLR3^−/−/TLR7^−/−, MyD88^−/−, or wt mice were infected with MHV A59 (moi = 1) or treated with CpG oligonucleotides. IFN-α in tissue culture supernatants was determined 24 hours after infection by ELISA. Bars represent means with values from individual mice shown as open circles. Statistical analysis was performed using Student t test (**P < .01).