Immune response of neonates to pneumococcal polysaccharide-protein conjugate.

Immune responses were studied in adult and young mice exposed to pneumococcal 6A and 19F polysaccharides (PSs), as well as 19F PS conjugated to proteins, e.g. human immunoglobulin G (HIgG), pneumococcal R61 cell wall polypeptide, and bovine serum albumin (BSA). Significantly higher IgM and IgG2 antibody titres were induced in mice receiving 19F PS-protein conjugates than in the control group receiving 19F PS alone. Maternal immunization with 19F PS-HIgG conjugate elicited a low immune response in the offspring. However, when young mice from immunized mothers were given and additional dose of polysaccharide-protein conjugate, they gave an antibody response greater than that of mice not given additional immunogen. Similarly, young mice exposed to 14-valent pneumococcal vaccine during gestation produced higher antibody response to 6A and 19F PSs. Secondary immunization of 19F PS or PS-protein conjugate at 1 or 2 weeks after primary immunization did not enhance antibody formation but rather suppressed the immune response to that polysaccharide.