FIG 4.

Viral load in BALF and neutralizing-antibody titer in serum. (A) Genome equivalent copies (GEC) in bronchoalveolar lavage fluid (BALF) were determined by qRT-PCR and are shown over the course of the infection and for PBS-treated control animals. The limit of detection (LOD) (17,200 GEC/ml) of the qRT-PCR assay was empirically determined using plasmid DNA and is indicated by the dashed line. Values in parentheses give the number of PCR-positive animals and the total number of animals. (B) Infection strain-neutralizing antibodies in blood were assessed by serum neutralization tests. Titers are expressed as the reciprocal 50% neutralizing dose (ND₅₀). Data on 30 infected animals are shown, with lines linking values of individual animals. Numbers in diamonds indicate the number of animals with a certain reciprocal ND₅₀ value at a given time point.