PTX3 enhances PB and PC expansion as well as IgG production in response to encapsulated bacteria. (A and B) ELISA of serum SP-reactive IgG2b, IgG2c, IgG3, and IgM (A) and ELISPOT of splenic SP-reactive antibody-secreting cells (ASCs; B) from WT and Ptx3^−/− mice after i.v. injection (d7) of live SP. RU, relative units. (C) Flow cytometric quantification of frequency (left cytograms) and absolute number (right graphs) of B220⁻CD138⁺ PBs/PCs expressing IgM or class-switched IgG2b, IgG2c, and IgG3 from WT and Ptx3^−/− mice after i.v. injection (d7) of live SP. Dashed lines show the mean frequency or absolute number in nonimmunized WT mice. Similar values were obtained in nonimmunized Ptx3^−/− mice. (D) qRT-PCR of mRNA for AID (Aicda) in splenic B220⁻CD138⁺ PBs/PCs from WT and Ptx3^−/− mice after i.v. injection (d7) of live SP. Results are normalized to mRNA for HPRT and are presented as relative expression (RE) compared with PBs/PCs from WT mice. (E) Flow cytometric quantification of frequency of splenic B220⁻ PBs expressing extracellular (extra) but not intracellular (intra) IgG2b, IgG2c, or IgG3 (left) as well as splenic B220⁻ PCs expressing both extracellular and intracellular IgG2b, IgG2c, or IgG3 (right) from WT and Ptx3^−/− mice after i.v. injection (d7) of live SP. Dashed lines show the mean frequency or absolute number in nonimmunized WT mice. Similar values were obtained in nonimmunized Ptx3^−/− mice. (F) IFA of spleens stained for MMP9 (green), IgG2c (red), and MOMA-1 (blue) from WT and Ptx3^−/− mice after i.v. injection (d7) of live SP. Bars, 50 µm. (G) IFA of splenic tissue from SP-infected WT mice stained for MMP9 (green), IgG2c (red), and DNA (blue) from WT mice after i.v. injection (d7) of live SP. Bar, 3 µm. Data summarize at least two experiments with at least three mice in each experimental group (A–C and E) or one representative experiment of at least three with similar results (D, F, and G). Error bars, SEM. *, P < 0.05; **, P < 0.01; ***, P < 0.001 (two-tailed Student’s t test).