Immune response to pneumococcal polysaccharides 4 and 14 in elderly and young adults: analysis of the variable light chain repertoire.

Streptococcus pneumoniae is a human bacterial pathogen responsible for serious infections including pneumonia. The currently licensed polysaccharide vaccine provides 60 to 80% protection in young adults, but in the elderly the vaccine efficacy is drastically reduced despite normal antibody levels. We hypothesized that the reduced vaccine efficacy in the elderly results from altered variable gene family usage. We have analyzed the light chain gene usage in 20 young (20 to 30 years of age) and 20 elderly (65 to 86 years of age) adults in response to pneumococcal polysaccharide 4 (PPS4) and PPS14. We generated a variable light chain library using B cells specific for PPS4 and PPS14 from each vaccinated individual. We determined complete sequences and somatic mutation frequencies in all isolated variable light chain fragments. Six gene families, kappa1, kappa2, kappa3, kappa4, lambda1, and lambda3, were identified in response to PPS4 and PPS14 in both age groups. Comparison of young and elderly adults demonstrated significant differences in kappa4, lambda1, and lambda3 gene usage in response to PPS4 and PPS14. With aging, there was a significant increase in kappa4 gene usage and a significant decrease in lambda1 and lambda3 gene usage in response to both PPS4 and PPS14. Although both Vkappa1 and Vlambda3 gene products demonstrated extensive mutations, there was no age-related difference in mutational frequency per gene family. These findings suggest an age-related change in light chain gene usage in response to PPS4 and PPS14.