PS3-specific BM plasma cells are sufficient to promote full protection against Streptococcus pneumoniae infections. Ten-week-old mice were immunized with PS3 or PS3 followed 2 days later by injection of CpG1668 and irradiated or not 45 days later. Fifteen days after irradiation, 2 mice per group were checked for depletion of total B-1, B-1a, B-1b, and B-2 cells in peritoneal washings as well for the frequency of the PS3-specific lymphocytes as described in Figure 6A and B. In all irradiated groups, B-cell depletion was superior to 98% irrespective of the B-cell subset considered, and the frequencies of PS3-specific lymphocytes in peritoneal washings were reduced at least 100-fold compared with control mice. Fifteen days after irradiation, the survival of nonirradiated and irradiated immune mice (8 per group) was then monitored after challenge with 106 (A) or 107 cfu (B) of live S pneumoniae.
