This finding suggests that most preterm infants are able to mount a specific cellular immune response [24]. In the present study, the time of immune evaluation, three months after the booster dose, could be stated as a limitation. It is possible that the antibody titers

and numbers of circulating tetanus-specific T cells may have decayed from peak levels three months after vaccination. Antibody levels following a booster dose usually peak after 15 and 30 days. The antigen-specific IFN-producing cells most probably are found among circulating Peripheral blood mononuclear cells 1–2 weeks after vaccination very transiently, thereafter, they rapidly reach the lymph nodes and then decay with time [24], [25], [26] and [27]. With the increase in the survival rate of premature infants at progressively younger gestational ages and the growing use of therapeutic resources, Gefitinib premature infants currently exhibit different characteristics from those of past decades [28] and [29] and factors other than prematurity itself may learn more be involved in the immune response. Thus, apart from the direct comparison of antibody levels between groups, linear and logistic regression analyses were performed to control for variables that may affect the response to vaccination. It should be

pointed out that the same independent variables were incorporated into all multiple linear and logistic regression models, which DNA ligase contributes to the consistency of the findings. Breastfeeding for more than six months was associated with a 3.5 fold increase in the chance of having optimal protective antibody levels against tetanus at 15 months of age, and a 0.96 IU/mL (95% CI: 0.08–1.83) increase of antibody levels 3 months after the booster dose. However, given the significantly lower rates of breastfeeding in premature infants, the effect observed of breastfeeding could be a confounding of other factors (e.g. gestational age, affinity maturation, etc.) that could influence the antibody response levels in these infants. However, this effect has also been

described by Greenberg et al. [30], who found high levels of antibodies among children who received a conjugated vaccine against H. influenzae type b and tetanus toxoid and had been breastfed until at least six months of age. Jeppesen et al. [31] found a correlation between breastfeeding and the population of T CD8+ cells. It is suggested that breastfeeding contributes to the structural and functional development of the thymus and the control of the apoptosis of immature thymocytes, which subsequently transform into CD4+ T and CD8+ T cells [32]. The use of antenatal corticosteroids, nutritional status and erythrocyte transfusions were not associated with the humoral response to the tetanus vaccine at 15 and 18 months, which is in agreement with findings described in previous studies [5], [8], [9], [10] and [33].