Percentiles of Lymphocyte Subsets in Preterm Infants According to Gestational Age Compared to Children and Adolescents.

Preterm newborns show an increased susceptibility to infections, conceivably related to their immature immune system. To gain further knowledge about the immune development in early preterm infants, we aimed to establish references for lymphocyte subsets and compare the maturation process during hospitalization to healthy term-born children and adolescents. For this purpose, peripheral blood samples (n = 153) were collected from 40 preterm infants, gestational age (GA) 26-30 week between 2nd and 6th day of life, and were monitored in intervals of every 2 or rather 4 weeks until the end of hospitalization. Furthermore, we analysed single sample controls of 10 term neonates. We compared these data with results of a study in healthy children and adolescent (n = 176). Flow cytometry of immune cell subsets was performed as single-platform analysis using 10-colour flow cytometry. Based on preterm's age, our percentile model allows readout of absolute cell count for lymphocytes, B cells, T cells, NK cells, T8 and T4 cells. The median (minimum) value of T-, B- and NK cells after birth was 2800 (600), 790 (120) and 140 (20) cells/μl, respectively. Major differences were found in absolute cell numbers of B cells, and in the frequency of regulatory T cells, most pronounced in the earliest preterm infants (GA 26). Compared to healthy children and adolescents, preterm infants reached lymphocyte counts in between the 5th and 50th percentile when discharging the hospital. This prospective observational study provides reference percentiles for lymphocytes subsets of preterm infants. These data are conducive to interpret immunological capability of preterm infants with possible immune disorders appropriate.