Preimmunization and postimmunization pneumococcal antibody titers in children with recurrent infections.

BACKGROUND: Patients with recurrent infections and normal IgG levels may have an abnormal response to pneumococcal polysaccharides. The ability to develop antibodies against different pneumococcal polysaccharides develops gradually in the first years of life, but the sequence of development and the influence of preexisting antibody titers has not been defined.

METHODS: Preimmunization and postimmunization IgG antibody titers against pneumococcal serotypes 3, 7F, 9N, and 14 were evaluated in a population of 100 1- to 18-year-old children referred to a pediatric allergy-immunology clinic because of recurrent respiratory infections. None of the patients had a known immunodeficiency syndrome; all had normal total IgG levels. Postimmunization antibody levels were obtained 4 to 6 weeks after immunization. Patients less than/=5 years of age who failed to develop antibody levels above 200 ng Ab N/mL against any serotype and older patients who failed to develop these levels against a second serotype in addition to serotype 3 were considered for IgG replacement therapy.

RESULTS: Prior to immunization, 50% of 51 patients did not have protective antibody levels against any of the serotypes tested. Immunization induced a high response to serotype 3 in all age groups, but responses to serotypes 7F and 14 increased with age. Five of 78 patients (6.4%) failed to develop protective antibody levels against any serotype tested. Three of these patients had clinical criteria that justified the use of IgG replacement therapy; all improved. Three patients were re-immunized 1 to 2 years after the first immunization and all developed protective levels of antibodies against serotype 3 after the second immunization.

CONCLUSION: We conclude that, although measurement of antibody levels against pneumococcal serotype 3 allows a good differentiation of patients who are able to develop anti-polysaccharide antibodies from those who are not, further studies of the development of specific antibodies against other vaccine serotypes in normal populations of different ages are needed to define a normal response to pneumococcal polysaccharides.