TLR4 and infection: The amount of replicating virus detected in the lungs at various time points p.i., was not significantly different between the WT and TLR4−/− mice and in both groups the virus was cleared efficiently from the lungs by day 7 p.i. To determine whether the absence of TLR4 affected protection from subsequent reinfection, we investigated viral replication in WT and TLR4−/− mice challenged with hMPV six weeks after primary infection.