Type I diabetes mellitus (DM) has been associated with abnormalities of T cells. Our objective was to assess whether antibody responses to T-cell-dependent and -independent antigens in children with DM are lower than those of children without DM. We performed a case-control study matching children with DM to children without DM by age and by assessing antibody levels to pneumococcal serotypes, Haemophilus influenzae, and tetanus and diphtheria toxoids and reassessing antibody levels in patients with antibody levels below protective thresholds after booster immunization. We recruited 36 children with DM and 36 age-matched controls. The mean age was 10 years. There was no difference between groups in antibody levels against the antigens tested. Pneumococcal antibody levels below the protective threshold were found in 35.9% of DM patients after conjugate pneumococcal vaccination with no difference between groups. Booster immunization with unconjugated pneumococcal vaccine resulted in a median level against pneumococcal serotypes of 2.3 g/ml (range, 0.05 to 664.7 g/ml) in children with DM and 6.1 g/ml (0.12 to 203.36 g/ml) in children without DM (P ؍ 0.013). Over 85% of children had levels above the protective threshold after booster immunization with no difference between groups. There was no evidence for a reduced antibody response to T-cell-dependent antigens given during childhood immunizations in children with DM. There was a reduced antibody response to antigens of pneumococcal strains in children with DM given unconjugated pneumococcal polysaccharide vaccine compared to that of children without DM without being associated with a difference in percentage of antibody levels below the protective threshold between groups.T ype I diabetes mellitus (DM) has been associated with multiple abnormalities of T-cell function and quantities. In the first ground-breaking studies, decreased CD4/CD8 lymphocyte ratios, reduced lymphocyte blastogenesis, and acquired defects in interleukin-2 production were observed in people affected by DM (1, 2, 3). Subsequent research revealed reduced T-cell primary responses to protein antigens (4). Other investigations demonstrated features of a suppression of a T-helper cell 1 phenotype, with reduced expression of Th1-associated chemokine receptors and decreased secretion of Th1 cytokines (5).A previous study showed that compared to healthy controls, adult DM patients mounted a significantly impaired primary antibody response to T-cell-dependent primary protein antigens used for immunization, like hepatitis A vaccine and diphtheria toxoid, while the response to the T-cell-independent pneumococcal polysaccharide vaccine was not different. Patients with type II diabetes showed a normal response to immunization, illustrating that hyperglycemia is not involved in a change of the immune response (6).People with DM are susceptible to bacterial and particularly pneumococcal infection and are at increased risk of morbidity and mortality from bacteremia due to Streptococcus pneumoniae (7,8).Ther...