Developmental immaturities in neonatal host defense predispose the neonates to an increased mortality rate during bacterial infections. Early diagnosis is of great clinical importance, but, especially in neonates, is sometimes very difficult. The ability to generate reactive oxygen species, the so-called respiratory burst, is essential for neutrophils to kill infectious microorganisms. Therefore, changes of respiratory burst may reflect increased susceptibility of neonates to infections and may be useful for the early detection of infections. Superoxide anion production was determined by a flow cytometric method using dihydrorhodamine 123 (DHR) as an oxidative probe after priming of neutrophils with PBS buffer (spontaneous burst), with N-formyl-methionyl-leucyl-phenylalanine (fMLP), or with Escherichia coli. During the study period, the spontaneous percentage of activated cells in whole blood as well as the percentage of activated cells in stimulation with fMLP was lower in adults (n = 100; PBS, 1.0 +/- 0.1%; fMLP, 8.3 +/- 0.9%) compared with neonates without signs of infection (n = 143). Among the latter, the percentage of activated cells (PBS and fMLP assay) varied with respect to gestational age and hours of life: lowest values were measured in preterm newborns with gestational age less than 32 wk and between 25 and 120 h of life. The same correlation to gestational age was true for total neutrophil cell counts. In neonates with increased levels of C-reactive protein during the first 5 d of life (n = 43), the percentages of activated cells after PBS and fMLP incubation were higher than those of neonates without signs of infection. The relationship of neutrophil respiratory burst and neutrophil cell counts to gestational age might reflect at least in part a reason for the increased susceptibility of neonates to infections. Furthermore, determination of respiratory burst may prove to be a new laboratory parameter of neonatal infection.

Low HLA-DR expression on monocytes contributes to impaired neonatal host defense, especially in preterm neonates.

Bacterial infections, even without any perinatal risk factors, are common in newborns, especially in preterm neonates. The aim of this study was to evaluate possible impairment of neutrophil chemotaxis in term and preterm neonates compared with adults as well as neonates with different modes of delivery and anaesthesia. We analysed the expression of the adhesion molecule L-Selectin as well as shape change, spontaneous and N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced transmigration of neutrophils in a flow cytometric assay of chemotaxis after spontaneous delivery with Cesarian Section (CS) under spinal anaesthesia (mepivacaine, sufentanil), epidural anaesthesia (ropivacaine or bupivacaine, sufentanil) or general anaesthesia (ketamine, thiopental, succinylcholine). Chemokinesis was higher (p=0.008) in cord blood neutrophils than in the adult ones, whereas those could be more stimulated by fMLP (p=0.02). After vaginal delivery neutrophils showed a higher spontaneous and fMLP-stimulated chemotactic response compared to neonates after CS without labor. Comparing different types of anaesthesia for CS, spinal anaesthesia resulted in less impairment on chemotaxis than general anaesthesia or epidural anaesthesia. The new flow cytometric assay of neutrophil chemotaxis is an appropriate and objective method to analyse functional differences even in very small volumes of blood, essential in neonatology. Term neonates do not show reduced chemotaxis compared to adults. Preterm neonates present with reduced chemotaxis and chemokinesis, confirming the well known deficits in their neutrophil function. The side effects of maternal drugs on the neonatal immune system have to be considered especially when the immune response is already impaired, as in preterm infants.