Objective: Preterm infants respond to respiratory distress syndrome (RDS) with systemic inflammation. Whether adaptive immunity is activated in these infants is not known. Therefore, we set out to study the activation of circulating T cells during the first week of life in preterm infants with and without RDS.
Methods: We studied 34 infants (gestational age 27.1 weeks (2.0), body weight 900 g (216)) requiring surfactant treatment and mechanical ventilation due to RDS and 21 preterm infants (gestational age 32.6 weeks (1.4), body weight 1697 g (406)) without RDS. Blood samples were taken on postnatal days 1, 3 and 7. Helper (CD4+) and cytotoxic (CD8+) T-cell counts and proportions of T cells expressing CD54 and CD62L were determined by flow cytometry.
Results: As compared with infants without RDS, infants with RDS had fewer CD4 and CD8 T cells on day 3 (p = 0.03 and p = 0.02). On day 1 and day 3, a greater proportion of their CD4 T cells expressed CD54 (p = 0.001 and p = 0.03) and a lower proportion of their CD8 T cells expressed CD62L (p = 0.02 and p = 0.05). Of the infants with RDS surviving past 36 gestational weeks, 17 infants developed bronchopulmonary dysplasia (BPD). Compared with those surviving without BPD (N = 15), infants with BPD had a greater proportion of CD8 T cells expressing CD54 on day 1 and day 3 (p = 0.02 and p = 0.01).
Conclusions: In preterm infants RDS is associated with the activation of both helper and cytotoxic T cells. Increased activation of cytotoxic T cells is found in those who subsequently develop BPD. Activation of adaptive immunity may provide a link between acute and long-term morbidity in preterm infants with RDS.