The efficacy of different
vaccines in protecting elderly individuals against
Streptococcus pneumoniae infections is not clear. In the current study, aged mice (22-25 months old) exhibited significantly increased susceptibility to respiratory
infection with serotype 3 S. pneumoniae relative to younger adult mice, regardless of whether mice were naive or immunized with native pneumococcal
polysaccharide (PPS; Pneumovax23) or
protein-PPS conjugate (Prevnar-13)
vaccines. Nonetheless,
Pneumovax-immunized aged mice developed limited
bacteremia following respiratory challenge and exhibited significantly increased survival following systemic challenge relative to
Prevnar-immune aged mice and young mice that had received either
vaccine. This was explained by >10-fold increases in PPS-specific
immunoglobulin G (
IgG) levels in
Pneumovax-immunized aged mice relative to other groups. Remarkably, PPS3-specific B-cell expansion,
IgG switching, plasmablast differentiation, and spleen and bone marrow antibody-secreting cell frequencies were 10-fold higher in aged mice following
Pneumovax immunization relative to young mice, due to significantly increased B-1b cell participation. In summary, this study highlights (1) the need to devise strategies to enhance respiratory immunity in aged populations, (2) the diverse responses young and aged populations generate to
Pneumovax vs
Prevnar vaccines, and (3) the potential value of exploiting B-1b cell responses in aged individuals for increased
vaccine efficacy.