Opsonophagocytic activity assays
Blood samples were collected approximately 1 month postvaccination.
Functional antibacterial OPA antibodies were measured
using 13 serotype-specific validated microcolony OPA assays
[3]. The microcolony OPA assay used in this study was a modification
of the method of Romero-Steiner et al. [4], and was based on
previously described methods [3,5]. Assay titers were defined as the
interpolated reciprocal serum dilution that results in complementmediated
killing of 50% of the bacteria in the assay. The lower limit
of detection (LOD) is a titer of 1:8 (same for each serotype-specific
OPA assay). The lower limit of quantitation (LLOQ) was determined
for each serotype-specific assay during assay validation. OPA
titers >LLOQ were considered accurate and their quantified values
reported. Titers