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.

A novel approach to study variable heavy chain gene usage in response to the capsular polysaccharide of Neisseria meningitidis serogroup C.

The molecular mechanisms involved in the relatively poor immune response in the elderly are not clearly understood. Qualitative aspects of the immune response could be a possible explanation for the differential response to T-independent antigens in young adults and elderly. This study is directed towards elucidating the differential usage of variable heavy chain by young adult and elderly derived sequences in response to the capsular polysaccharide of Neisseria meningitidis serogroup C. We currently report findings of a preliminary study designed to test the feasibility of a novel approach to isolate antigen-specific B cells. Paramagnetic beads coated with an anti-idiotypic antibody, which mimics the capsular polysaccharide of N. meningitidis serogroup C, were used to select B cells. Analysis of the gene usage data indicates some unexpected differences in the use of variable chain heavy chain in the case of young adult versus elderly sequences. The elderly derived sequences use a more diverse array of V(H) gene families in contrast to the young adult sequences, where the V(H) gene family usage is restricted. Nearly half the young adult sequences utilize V(H)3-15 germline sequence while only 25% of the elderly sequences use this germline sequence. There were interesting differences in the types of JH chain and the composition and length of CDR3 utilized by the two groups. Together, these significant differences may contribute towards the poor immune response to T-independent antigens in the elderly. These data validate the techniques used for these studies and suggest that it is pertinent to use this approach towards future investigations to elucidate gene usage in response to an antigen.