Figure 4.

Expression of the homeostatic chemokine CCL19, CCL21 and CXCL13 in the spleen of young and aged mice 18 hours post-immunization. Snap-frozen spleen portions were homogenized and analyzed for CCL19, CCL21 and CXCL13 mRNA content by real-time PCR (A), or for CCL19 and CCL21 protein content by ELISA (B). Data represent the mean ± SEM of 5-8 mice/group. Statistical significance was determined by unpaired Student’s t test. ***, p<0.0001. (C) Localization of CCL21 expression by immunofluorescence staining of frozen spleen sections showing the B cell follicles using B220 staining (green) and CCL21 (red). The figure shows 3 representative spleen sections from young (i-iii) and aged (iv-vi) hosts of at least 10. Each panel shows whole spleen sections created from stitched images taken at a magnification of 200X. Scale bars represent 500 μm. (D) Localization of CXCL13 expression by immunofluorescence staining of frozen spleen sections from one representative young (left panel) and aged (right panel) host. The arrows point to the marginal zone expression of CXCL13 in young mice that is absent in aged mice. Pictures were taken at a magnification of 200X. Scale bars represent 100 μm. (E) Number of OTII donor cells recovered from the spleen of plt and WT hosts 1, 2, 3 and 4 days post-immunization. (F) CFSE-dilution profile of OTII donor cells recovered from plt and WT mice 3 days post-immunization. The gate delimits the undivided population (48.6% for plt mice and 1.5% for WT mice). Error bars represent the mean ± sem of 2-3 mice/group. Statistical significance was determine by 2-way anova followed by Bonferroni’s post-tests. ***, p<0.001 WT vs plt mice.