Toll-like receptor agonists allow generation of long-lasting antipneumococcal humoral immunity in response to a plain polysaccharidic vaccine.

Toll-like receptors (TLRs) are considered as potential targets for vaccine adjuvants. Here, we explored the impact of TLR agonists on the B cell response to a prototypic thymus-independent (TI) antigen: a Streptococcus pneumoniae capsular polysaccharide (PS). In adult mice, all TLR agonists (and CpG oligodeoxynucleotides [ODN] in particular) enhance the PS antibody response, provided that their administration is delayed until the second day after PS vaccination. In infant mice, CpG ODN not only potentiated the PS3 antibody response but also restored responsiveness to PS3 vaccination. Moreover, the immune protection induced by the plain PS3 vaccine adjuvanted by CpG ODN was comparable to that conferred by the conjugate vaccine in terms of efficiency and longevity. CpG ODN exert their adjuvant effect by increasing the survival rate of antigen-stimulated B cells as well as the output of plasmablasts. Our results provide a rationale for broader application of polysaccharidic vaccines.