Monocyte switch in neonates: high phagocytic capacity and low HLA-DR expression in VLBWI are inverted during gestational aging.

Pre-term neonates are at high risk to develop early-onset sepsis which possibly is caused by an immature immune system. Monocytes play a pivotal role as professional phagocytic and antigen-presenting cells in the innate immunity. In the present study, we investigated in monocytes from cord blood the expression of human leukocyte antigen (HLA)-DR as a marker for antigen-presenting capability, the expression of the high-affinity receptor for IgG (FcgammaRI/CD64), and the capacity to phagocytize non-opsonized Escherichia coli. We compared 70 infants in three groups according to their gestational age (group I: 20 very low birth weight infants (VLBWI), 24-31 weeks of gestation; group II: 25 pre-term infants, 32-36 weeks of gestation, and group III: 25 term neonates). The expression of CD64 as well as the phagocytic capacity of monocytes from cord blood were highest in VLBWI (p < 0.05 and p < 0.01, respectively). In contrast, HLA-DR expression was significantly (p < 0.05) diminished in VLBWI, which possibly leads to a reduced antigen-presenting capacity. We conclude that monocytes have different functional properties during gestational aging, which perhaps participate in the high incidence of infections in VLBWI.