FIG. 4.

Abundance of pulmonary CD8⁺ IFN-γ⁺ T cells on the indicated days following primary infection with wt RSV, RSV/IL-4, or placebo and on day 6 (day 33) following a challenge with wt RSV performed on day 27 (the mock control group was included in the challenge). The expression of CD8⁺ IFN-γ⁺ cells was made following specific stimulation in vitro using the RSV peptide epitope. Each cell population is expressed as the mean of the percentage of total PMC, with the standard error, based on four mice per group for wt RSV and RSV/IL-4 and one or two mice for mock infection. The total PMC were isolated, stimulated with the RSV-specific peptide as described in Materials and Methods, stained for CD8, permeabilized, stained for IFN-γ, and analyzed by flow cytometry. The data for day 9, when the difference between the wt RSV and RSV/IL-4 groups was statistically significant (P < 0.05), are indicated by a star. On days 4, 5, 7, and 12, the fraction of IFN-γ⁺ cells in the mock-infected group was very low and cannot be seen with this scale.