The immune response to pneumococcal polysaccharides 14 and 23F among elderly individuals consists predominantly of switched memory B cells.

The phenotype of B cells that respond to vaccination with the purified pneumococcal polysaccharide (PPS) has been a topic of debate. We have recently identified the phenotype of cells from healthy young volunteers as CD27(+)IgM(+) B cells. However, the PPS-responding B-cell population has not yet been identified in high-risk populations, such as elderly individuals. Previous studies have shown that elderly individuals have a lower percentage of immunoglobulin M memory B cells than healthy young adults. In this study, we directly characterized the phenotype of PPS-specific B cells before and after vaccination with PPS vaccine (PPV) in elderly adults, using fluorescently labeled PPS14 and PPS23F. In contrast to our observations in healthy young volunteers, the PPS-responding B-cell population consisted primarily of switched memory (CD27(+)IgM(-)) B cells. In concurrence with these findings, postvaccination immunoglobulin M concentrations were not significantly increased in this population, and the opsonophagocytic response was decreased, compared with that in young adults. These findings identify a significant shift in the phenotype of the B-cell population in response to PPV among elderly individuals.