Old mice have increased numbers of circulating and recruited Ly6C^high monocytes during the course of <i>S</i>. <i>pneumoniae</i> colonization.

<p>(A) Colony forming units (CFUs) in nasal lavages from young and old WT mice were quantified on days 3, 7, 14 and 21 following intranasal colonization with <i>S</i>. <i>pneumoniae</i> (± SEM; <i>n</i> = 5–22). (B) CFUs of <i>S</i>. <i>pneumoniae</i> in the lungs at day 3 following intranasal colonization (± SEM; <i>n</i> = 9–22). (C) Survival of young and old mice after intranasal <i>S</i>. <i>pneumoniae</i> colonization (± SEM; <i>n</i> = 12). (D) Total serum CCL2 in young and old mice following intranasal <i>S</i>. <i>pneumoniae</i> colonization was measured by a high sensitivity ELISA. The data represent the mean (± SEM) of 3 mice per time point. (E) Ly6C^high monocytes as a percent of CD45⁺ cells in the blood of young and old WT mice during nasopharyngeal <i>S</i>. <i>pneumoniae</i> colonization (± SEM; <i>n</i> = 5–8) was measured by flow cytometry. (F) Mean expression of F4/80 on Ly6C^high monocytes in the blood of old mice during <i>S</i>. <i>pneumoniae</i> colonization is decreased as compared to young mice. (G) Levels of CCL2 transcript in the nasopharynx during the course of <i>S</i>. <i>pneumoniae</i> colonization were measured by quantitative PCR. (± SEM; <i>n</i> = 3). (H-I) Total numbers of (H) Ly6C^high monocytes and (I) macrophages detected by flow cytometry in the nasopharnyx of young and old mice during <i>S</i>. <i>pneumoniae</i> colonization (± SEM; <i>n</i> = 3–8). (J) Mean F4/80 expression on nasopharyngeal macrophages is lower in old mice during <i>S</i>. <i>pneumoniae</i> colonization (± SEM; <i>n</i> = 3–8). Statistical significance was determined by two-tailed Mann-Whitney-Wilcoxon test, one-way or two-way ANOVA with Fisher's LSD post-test. (K) Circulating blood monocytes from old mice bind fewer TRITC-labelled <i>S</i>. <i>pneumoniae</i> (4°C) but there is no difference in internalization of the bacteria (37°C). Survival in (C) was determined by the Mantel-Cox Log-rank test. * indicates <i>p</i> < .05, ** indicates <i>p</i> < 0.005, *** indicates <i>p</i> < 0.0005 and **** indicates p < 0.00005. (A-J) is representative of 3 independent experiments.