Pneumococcal polysaccharide vaccination induces polysaccharide-specific B cells in adult peripheral blood expressing CD19⁺CD20⁺CD3⁻CD70⁻CD27⁺IgM⁺CD43⁺CD5⁺/⁻.

Pneumococcal polysaccharide vaccines have been used to elicit a protective anti-pneumococcal polysaccharide antibody response against Streptococcus pneumoniae in healthy individuals. Identifying human B cells which respond to T-cell independent type-2 antigens, such as pneumococcal polysaccharides, has been challenging. We employed pneumococcal polysaccharides directly conjugated to fluorophores in conjunction with flow cytometry to identify the phenotype of B cells that respond to pneumococcal polysaccharide vaccination. We have previously identified that the majority of pneumococcal polysaccharide-selected cells responding to vaccination are CD27(+)IgM(+) (IgM(+) memory) cells. In this study, we further characterized pneumococcal polysaccharide-selected cells in the peripheral blood to better identify how the various B cell phenotypes responded 7 and 30 days post-immunization. We show that 7 days post-immunization the majority of pneumococcal polysaccharide-selected IgM(+) memory cells (PPS14(+) 56.5%, PPS23F(+) 63.8%) were CD19(+)CD20(+)CD27(+)IgM(+)CD43(+)CD5(+/-)CD70(-), which was significantly increased compared to pre-immunization levels. This phenotype is in alignment with recent publications describing human B-1 cells. PPS-responsive B cells receded to pre-immunization levels by day-30. These findings suggest that this B-1 like cell population plays an important role in early responses to S. pneumoniae infection and possibly other T-cell independent type-2 antigens in humans.