FIG. 5.

Localized memory CD4 T-cell-directed responses in the lung are distinct from diffuse T-cell distribution during primary infection. (A) Localization of CD3⁺ T cells in the lungs of uninfected C57BL/6 mice (top) and influenza virus-infected C57BL/6 mouse recipients of total CD4 T cells from naive (middle left) or C57BL/6 flu-memory (lower left) mice 7 days after infection with X31, using immunohistochemistry. Similar CD3 immunohistochemistry analysis was performed on lungs from PR8-infected RAG2^−/− mice that received total CD4 T cells from naive (middle right) or C57BL/6 flu-memory (lower right) mice (see Fig. 6). CD3⁺ T cells stain brown, as indicated by arrows, and images for representative animals of five mice per group are shown at a magnification of ×20. (B) CD3 T cells were enumerated by counting the total number of cells staining for CD3 and taking the average for five 1-mm² sections of lung per animal. Each section counted had a similar lung architecture. Data shown are the average counts for five animals per group. ***, P < 0.001, representing the difference in CD3 numbers between groups, as determined by ANOVA.