SPECIFIC ANTIBODY-RESPONSES TO DIPHTHERIA TETANUS REVACCINATION IN CHILDREN EVALUATED FOR IMMUNODEFICIENCY/

Background: Assaying specific antibody levels against well-defined ant igens such as diphtheria (D), tetanus (T), and more recently Haemophil us is used as one indicator of humoral immune reactivity when evaluati ng patients for immunodeficiency. The nature of the response to booste r vaccine in this group of patients is not well defined. Objective: To define the response to D/T booster vaccination in patients with nonpr otective antibody levels in order to distinguish immunocompetent from immunodeficient children. Methods: Patients between the ages of 16 mon ths and 17 years referred for possible immunodeficiency were assessed for specific antibody levels as part of a standard immunologic evaluat ion. Twenty-six previously immunized patients had antibody titers less than or equal to 0.2 IU against D and/or T or another abnormal vaccin e response. All of these patients received boosters of diphtheria and tetanus vaccine (D2T5). Diphtheria and tetanus antibody levels were as sayed 4 weeks following booster vaccination. Results: Of the twenty-si x subjects, a subset of patients (6) failed to show significant elevat ions in specific-serum antibody titers to diphtheria and/or tetanus an d were thus labeled nonresponders. These patients were retrospectively compared with their responder counterparts examining specific antibod y titers pre-immunization and post-immunization, serum immunoglobulins , and clinical presentation. The groups showed no significant differen ce in baseline specific antibody measures but following re-immunizatio n responders showed a 31.34-fold and 22.33-fold increase in D and T an tibody levels, respectively. In contrast, nonresponders produced only a 2.62-fold to D and 6.15-fold increase to T (all group comparisons P < .05). Clinical presentation also tended to be more severe in the non responder group. Conclusions: These data stress the importance of spec ific antibody titers preimmunization and post-immunization in the asse ssment of immunodeficiency states, and emphasize the different charact eristics of responses between diphtheria and tetanus toxoids. The abil ity to achieve the minimum protective antibody level does not necessar ily denote immune competence. Serum immunoglobulin levels and baseline antibody titers are insufficient for the functional assessment of the immune response, The ability to generate antibody responses following booster vaccination is a more complete measure of overall immune comp etence and should be considered when evaluating patients for replaceme nt immunoglobulin therapy.