FIG 2.
Comparison of URT and LRT-plus-URT MuHV-4 infections. (a) BALB/c mice were inoculated i.n. with MuHV-4 under anesthesia (104 PFU in 30 μl). After 2 days, lung sections were stained for viral antigens (brown) and counterstained with Mayer's hemalum (blue) to reveal infection of the lung alveoli (arrows). (b) BALB/c mice were inoculated i.n. with MuHV-4 without anesthesia (105 PFU in 5 μl). After 2 days, nose sections were stained for viral antigens as for panel a to reveal infection of the olfactory neuroepithelium (open arrows), but not the adjacent respiratory epithelium (filled arrows). (c) Mice were inoculated with MuHV-4 as for panel a (LRT plus URT) and then analyzed for URT infection as for panel b. Again, the olfactory neuroepithelium was infected. (d) Mice were inoculated with MuHV-4 as for panel b (URT) and then analyzed for LRT infection as for panel a. No viral antigens were detected. (e) BALB/c mice were inoculated i.n. with luciferase+ MuHV-4 either in the LRT plus URT as for panel a or in the URT as for panel b. Infection was then imaged by serial luciferin injection and CCD camera scanning. A representative image is shown for each time point. LRT-plus-URT inoculation led to lung and nose infections. At day 15, infection is seen in the SCLN and spleen. URT inoculation produced detectable infection only in the nose and SCLN. p/s/cm2/sr, photons/second/cm2/steradian. (f) Quantitation of luciferase signals, as illustrated in panel e, showing the mean ± SEM of 3 to 6 mice per time point. The dashed lines show the lower limit of assay sensitivity. Day 5 nose and SCLN signals were significantly higher with URT than with LRT-plus-URT inoculation (P < 0.005). (g) Mice were inoculated with MuHV-4 in either the URT or LRT plus URT. Splenic infection was then tracked by infectious-center assay. Splenic virus titers were significantly higher after LRT-plus-URT inoculation at days 7 to 17 (P < 0.005), but not at days 21 to 30 (P > 0.3). The lower limit of assay sensitivity was 102 infectious centers/spleen.