Background. Repeated immunizations with polysaccharide (PS) vaccines cause hyporesponsiveness through undefined mechanisms. We assessed the effects of a PS booster on immune responses, frequency, and survival of PS-specific B-cell subpopulations in spleen and bone marrow. Methods. Neonatal mice were primed with meningococcus serotype C (MenC) conjugate MenC-CRM 197+CpG1826, boosted with MenC-CRM 197, MenC-PS, or saline; subsequently, bromodeoxyuridine (BrdU) was injected daily intraperitoneally. MenC-PS-specific cells were labeled with fluorescent MenC-PS and phenotyped by flow cytometry. Results. After MenC-PS booster, proliferating (BrdU +) MenC-PS-specific naive B cells (CD138 -/B220 +; P =. 0003) and plasma cells (CD138 +/B220 -; P =. 0002) in spleen were fewer than after saline booster. BrdU + MenC-PS-specific plasma cells were also reduced in bone marrow (P =. 0308). Compared to saline, MenC-PS booster reduced BrdU + IgG + MenC-PS-specific B cells in spleen (P =. 0002). Twelve hours after the MenC-PS booster, an increased frequency of apoptotic (AnnexinV +) MenC-PS-specific B cells in spleen was observed compared with MenC-CRM197 (P =. 0286) or saline (P =. 001) boosters.Conclusions.We demonstrated that the MenC-PS booster significantly reduced the frequency of newly activated MenC-PS-specific B cells - mostly switched IgG + memory cells - by driving them into apoptosis. It shows directly that apoptosis of PS-specific memory cells is the cause of PS-induced hyporesponsiveness. These results should be taken into account prior to consideration of the use of PS vaccines.
Bibliographical noteFunding Information:
Financial support. This work was funded by The University of Iceland Research Fund and the Landspitali University Hospital Research Fund.