FIG. 2.

Binding of anticapsular antibodies (Ab) to radiolabeled group C polysaccharide. (A) When a high antigen dose is used both high- and low-avidity antibodies are detected. (B) When a low antigen dose is used, detection of higher-avidity antibodies is favored. It takes four- to fivefold-higher concentrations of anticapsular antibody from pool 4, a low-avidity pool, to give equivalent binding to that of antibodies in the CDC1992 reference pool. The dose-response binding of pool 3 in the low-antigen assay is between that of pool 4 and that of the CDC1992 reference pool, and pool 3 is calculated to have an intermediate avidity Ka between that of pool 4 and that of the CDC pool (Table 3).