To understand the modulation of immune response to polysaccharide (PS) immunogens and attempt to develop a more effective vaccine for prevention of pneumococcal diseases in young children, we studied the immune response of young mice to a type 9V PS-tetanus toxoid (TT) conjugate and the effect of maternal immunization on the immune response of young mice to 9VPS-TT. Young mice at 2 weeks of age produced IgM antibody to 9VPS or PS-protein conjugate. However, only 9VPS-TT conjugate induced an IgG antibody response and an anamestic effect when a second dose of the immunogen was injected at 2 weeks interval. Aluminum hydroxide gel enhanced the IgG antibody response to 9VPS-TT but did not augment the response to 9VPS. The gel also helped in the isotype switching from IgM to IgG. Maternal immunization before and/or during gestation primed young mice to respond effectively to 9VPS-TT conjugate immunogen. Injection of pregnant mice with the conjugate immunogen enhanced the IgG antibody response to 9VPS-TT in the offspring. These results indicated that immunization of mothers with an optimum dose of 9VPS-TT immunogen before and/or during pregnancy and in young children with a PS-protein conjugate can provide young children with an enhanced antibody response to pneumococcal PSs.
