Physical and Immunologic Properties of Pneumococcal Capsular Polysaccharide Produced during Human Infection

Abstract

A mean molecular weight of ≥ 100,000 was found for type-specific pneumococcal capsular antigens (PCA) present in sera, bullous fluid, and pleural or cerebrospinal fluids from 11 patients with pneumococcal infection and for type-specific purified pneumococcal polysaccharide vaccines (PPP). The molecular weight of serum PCA was not decreased by trypsinization or incubation of the PCA in serum at 37°C. PCA present in the urine of individuals with pneumococcal infection was markedly smaller than PCA present in the other body fluids. Urine PCA had only partial immunologic identity with PPP and reacted differently from PPP or PCA in other body fluids in immunoelectrophoresis. These differences could not be attributed to degradation of PCA by urine per se. The mean molecular weight of circulating PCA and its immunoreactivity in gel diffusion tests did not change with time. PCA present in the urine during periods of prolonged antigenemia was persistently different from the serum PCA in gel diffusion tests and had a low molecular weight. Urine PCA from different patients infected with the same pneumococcal type were immunologically identical in double diffusion tests. Low molecular weight PCA in the urine of individuals with pneumococcal infection may be derived from eigher selective renal excretion of low molecular weight PCA produced by the infecting pneumococci or from in vivo degradation of large molecular weight PCA produced during infection.