Fig. 8: Protection from pneumococcal infection fails in pIgR^−/− mice even when vaccinated with CPS14⁺MVs.

A Timeline of immunization, challenge with pneumococci, and sample collection. Six- to 8-week-old female pIgR^+/+ and pIgR^−/− mice were vaccinated with MVs (vector control) or CPS14⁺MVs three times at weeks 0, 3, and 6. At week 9, all the mice were intranasally inoculated with pneumococcal strain ATCC 700676 at the CFU of 2 × 10⁵. Vaccination groupings of mice are described in the right table, which shows the vaccine used, the amount of CPS14 per dose, the route, and the number of mice in each group. Twenty-four hours after infection, mice were euthanized, and the nasal wash and BALF samples were collected. Created in BioRender. Konig, S. (2025) https://BioRender.com/z8u1cwz. B Bacterial clearance in the nasal cavity of pIgR^+/+ and pIgR^−/− mice intranasally immunized with MVs (vector control) or CPS14⁺MVs. The nasal wash samples were analyzed by the CFU assay (left panel) and the real-time PCR assay (right panel). Representative data obtained from the pIgR^+/+ mice (n = 18) and pIgR^−/− mice (n = 17) are the combined results from 3 independent animal experiments. In total, 6- to 8-week-old female pIgR^+/+ mice (n = 18) and pIgR^−/− mice (n = 17) were used in this study. The number of the pIgR^+/+ mice vaccinated with MVs (vector control) or CPS14⁺MVs was 9. The number of pIgR^−/− mice vaccinated with MVs (vector control) or CPS14⁺MVs was 8 or 9, respectively. Shown are the individual data (dots) and mean with SD (bars) of the CFU/600 µL (left panel) and the copy numbers of the lytA gene/600 µL (right panel) in the nasal washes of pIgR^+/+ mice and pIgR^−/− mice, which were immunized with MVs (white bars) or CPS14⁺MVs (red bars). The numbers of open triangles indicate the samples under the limit of detection, which was 10² CFU (left panel) and 495 copies (right panel) in the CFU and real-time PCR assays, respectively. Asterisks denote statistically significant differences. Shown are the results of statistical analysis using the Mann–Whitney U-test. *P < 0.05. ** P < 0.01. ND: no statistically significant difference. No colony on the blood agar was detected from all the BALF samples (data not shown).