Kinetics of the Antibody Response to Type III Pneumococcal Polysaccharide (SSS-III)

Abstract A simple method was described for the preparation of 125I-labeled type III pneumococcal polysaccharide (SSS-III*) with a high specific radioactivity which retained the physical and immunologic properties of native SSS-III. SSS-III* was used to study the serum and tissue levels of antigen, as well as its excretion, after i.p. injection. When an optimally immunogenic dose (0.5 µg) of antigen was given, τ;90% of the injected antigen was excreted during the first 3 days after injection; however, after day 3, the SSS-III* which remained in each mouse was firmly bound to various tissues, and <5 ng SSS-III* was released into the circulation daily. SSS-III* was also used in a Farr test to measure serum antibody levels; the kinetics for the appearance of PFC/spleen and serum antibody levels were measured at 24-hr intervals after immunization with 0.5 µg of antigen. Maximum PFC/spleen were observed on day 4 after immunization whereas the peak serum antibody level was seen on day 5. The decay of serum antibody level from its maximum value was much slower than that of the PFC/spleen. The data describing the distribution of SSS-III in vivo and the measurement of serum antibody levels indicated that treadmill neutralization was not a factor in determining the serum antibody levels after immunization with an optimally immunogenic dose of SSS-III.