FIGURE 9.

I.n. exposure is not protective against subsequent S. pneumoniae challenge in old mice. Young (2-mo-old) and old (20- to 22-mo-old) C57BL/6 male mice were NP exposed to S. pneumoniae TIGR4, and (A) 3 wk later sera IgG levels against whole bacteria (TIGR4), PC, and purified PPS4 were assessed. Ab units were calculated based on a hyperimmune standard included in each ELISA plate, and the background titers, determined by ELISA of serum of naive mice within each group, were subtracted from the data (see Materials and Methods). Dotted lines represent limit of detection. Data were pooled from n = 7 young (black circles) and n = 5 old (gray circles) mice per group. (B) Mice were then challenged i.t. with 1 × 10⁶ CFU of S. pneumoniae TIGR4 and bacterial numbers in the blood and lungs of NP-exposed (filled bars) and naive (open bars) young and old mice were determined 48 h postchallenge. Bars represent mean ± SEM, and significant differences, determined by Student t test, are indicated by asterisks. Representative data from one of two independent experiments with n = 4 mice per group are shown. (C) Survival over time of young naive (O), young NP-exposed (■), old naive (◇)), and old NP-exposed (●) mice following i.t. challenge was also determined. (D) Naive, wild-type male mice received no serum or 250 μl of pooled serum from NP colonized young or old donors i.p., prior to challenge with S. pneumoniae TIGR4. Data were pooled from three independent experiments with a total of 15 mice per group. Boxed fractions denote survivors over total mice 2 wk after challenge and statistical significance (*p < 0.05) was calculated by the log-rank (Mantel–Cox) test. n.s., not significant.