CD30 signaling enhances expansion of B1a cells and PCs upon TI-2 immunization. (A) Mice were immunized with NP-Ficoll and analyzed 14 days postimmunization. Percentages of PCs (CD138⁺B220^lowGr1⁻Thy1.2.⁻CD11b⁻) and B1a cells (CD5⁺CD19⁺B220^low) in the spleen were determined by flow cytometry. Fourteen days after immunization, IgM- and IgG3-secreting PCs from the spleen were determined by ELISpot analysis (B) and serum titers of IgM and IgG3 antibodies binding to NP17-BSA were determined by ELISA (C). (D) Splenic sections from LMP1/CD30 and control (ctrl) mice were stained for GC B cells (PNA; blue), Metallic macrophages surrounding the primary follicles (MOMA; blue) and B cells (IgM; red/brown) 14 days after NP-CGG immunization. *P < .05, **P < .01, ***P = .001, ****P < .0001. ASC, antibody secreting cell.