Objectives: To determine systemic hypothermia's effect on circulating immune cells and their corresponding chemokines after hypoxic ischemic encephalopathy in neonates.
Design: In our randomized, controlled, multicenter trial of systemic hypothermia in neonatal hypoxic ischemic encephalopathy, we measured total and leukocyte subset and serum chemokine levels over time in both hypothermia and normothermia groups, as primary outcomes for safety.
Setting: Neonatal ICUs participating in a Neurological Disorders and Stroke sponsored clinical trial of therapeutic hypothermia.
Patients: Sixty-five neonates with moderate to severe hypoxic ischemic encephalopathy within 6 hours after birth.
Interventions: Patients were randomized to normothermia of 37°C or systemic hypothermia of 33°C for 48 hours.
Measurements and main results: Complete and differential leukocyte counts and serum chemokines were measured every 12 hours for 72 hours. The hypothermia group had significantly lower median circulating total WBC and leukocyte subclasses than the normothermia group before rewarming, with a nadir at 36 hours. Only the absolute neutrophil count rebounded after rewarming in the hypothermia group. Chemokines, monocyte chemotactic protein-1 and interleukin-8, which mediate leukocyte chemotaxis as well as bone marrow suppression, were negatively correlated with their target leukocytes in the hypothermia group, suggesting active chemokine and leukocyte modulation by hypothermia. Relative leukopenia at 60-72 hours correlated with an adverse outcome in the hypothermia group.
Conclusions: Our data are consistent with chemokine-associated systemic immunosuppression with hypothermia treatment. In hypothermic neonates, persistence of lower leukocyte counts after rewarming is observed in infants with more severe CNS injury.