Post-immunization pneumococcal antibody titers and IgG subclasses.

IgG antibodies against pneumococcal polysaccharides are found predominantly within IgG subclass 2. We wished to evaluate retrospectively IgG subclasses and post-immunization pneumococcal antibody titers in children with recurrent respiratory infections. We examined total immunoglobulin levels and IgG subclasses, as well as pneumococcal antibody titers against serotypes 3, 7F, 9N, and 14 present 4-6 weeks after pneumococcal immunization in 56 children 2-18 years old. Titers > 200 ng Ab N/ml to any of the 4 serotypes tested were arbitrarily considered protective. Four patients did not have protective antibody levels against any of the 4 serotypes tested following vaccination. Of those, 3 had normal IgG subclass levels and 1 had an IgG2 subclass deficiency. Of 3 additional patients with IgG2 deficiency, 2 had protective antibody levels to only 1 serotype and 1 had protective antibody levels to 2 serotypes. Furthermore, in 2 patients with undetectable IgG2 at the time of immunization, the response was only transient. We conclude that patients with IgG2 deficiency may not develop protective antibody levels to all pneumococcal serotypes and that some may have deficient memory for IgG anti-pneumococcal polysaccharide antibodies.