Lipid A binding to neonatal and adult red blood cells

Lipid A is responsible for the endotoxic activities of gram-negative bacteria. Binding of lipid A (50 micrograms/ml) to RBC was studied using a passive hemolysis test. RBC from adults, cord and venous RBC from full-term infants and RBC from preterm infants were studied. Lipid A sensitized RBC were hemolysed with anti-lipid A and guinea pig complement. Hemolysis was expressed as hemoglobin concentration (absorbance at 546 nm) in the supernatant after centrifugation. 50 micrograms/ml lipid A did not increase spontaneous hemolysis (< 3%) after 60 min of incubation in any of the four groups. The passive hemolysis test did not result in additional hemolysis (5%) of umbilical cord RBC. RBC of preterm infants showed a significant increase in hemolysis (24%) after 60 min of incubation. In RBC of full-term neonates, increased hemolysis (14 and 46%) was detected after 30 and 60 min of incubation. Adult RBC hemolysed stronger (26 and 64%) after 30 and 60 min than neonatal RBC. We conclude that lipid A binds less to neonatal RBC compared to adults.