OLIGOCLONALITY OF SERUM IMMUNOGLOBULIN-G ANTIBODY-RESPONSES TO STREPTOCOCCUS-PNEUMONIAE CAPSULAR POLYSACCHARIDE SEROTYPES 6B, 14, AND 23F

Serum antibodies (Abs) specific for the capsular polysaccharides of St reptococcus pneumoniae provide protection against invasive pneumococca l disease. Previous studies indicate that Abs to pneumococcal polysacc haride (PPS) serotypes I and 6B have limited clonal diversity, To dete rmine if restricted diversity was a feature common to other PPS specif icities, we examined the light (L)-chain expression and isoelectric he terogeneity of type 6B, 14 and 23F Abs elicited in 15 adults following PPS vaccination. At the population level, both PPS-6B and PPS-14 Abs expressed kappa and lambda chains, although 6B Abs more frequently exp ressed lambda chains lambda and 14 Abs more frequently expressed kappa chains, In individual sera, Abs were generally skewed towards either kappa or lambda expression. 23F-specific Abs had predominantly kappa c hains, Isoelectric focusing analyses showed that sera contained one or at most a few immunoglobulin G iib spectrotypes to all three respecti ve capsular serotypes, a result indicative of oligoclonality. A sequen ce analysis of a purified PPS-IJ-specific Ab having a single spectroty pe gave uniform amino-terminal sequences for both the heavy chain (VHI II subgroup) and the L chain (kappa III-A27 V region), From these resu lts we conclude that within individual adults, serum Ab responses to P PS serotypes 6B, 14, and 23F derive from a small number of dominant B- cell clones, and consequently variable-region expression is probably i ndividually limited as well. Oligoclonality appears to be a general ch aracteristic of human PPS-specific Ab repertoires, and H-e suggest tha t this property could lead to individual differences in Ab fine specif icity and/or functional activity against encapsulated pneumococci.