We investigated natural killer (NK) cell cytotoxicity in healthy preterm and full-term newborns in comparison to adults, to elucidate the possible role of delivery mode in influencing the NK activity and to evaluate the NK activity in severe neonatal pathological conditions such as bacterial sepsis and recurrent infections. NK cell cytotoxicity was investigated using a 4 h 51Cr release assay with K562 cells as targets expressed as percentage kill in the following study groups: full-term normal spontaneous vaginal delivery (n = 55), full-term caesarean section (n = 51), preterm normal spontaneous vaginal delivery (n = 34), preterm caesarean section (n = 28), bacterial sepsis (n = 15), recurrent neonatal infections (n = 8) and healthy adults aged between 22-42 years (n = 89). NK activity for the normal newborns was determined in paired cord and 2-4 day-old neonate blood. The NK cell cytotoxicity in healthy newborns was significantly lower than in adults (P < 0.01). Prematurity was associated with a significant decrease in NK cell activity compared to full-term neonates (P < 0.05). The mode of delivery did not influence the NK cytotoxicity. In sepsis and recurrent infections, a dramatic decrease in NK cell cytotoxicity was seen related to healthy newborns (P < 0.01).
Conclusion: Natural killer cell cytotoxicity is deficient in both neonatal sepsis and recurrent infections.