Diminished cord blood lymphocyte L-selectin expression in neonatal bacterial infection.

L-Selectin, a leukocyte surface glycoprotein involved in white blood cell extravasation, is rapidly down-regulated after leukocyte activation. We prospectively determined lymphocyte L-selectin expression in freshly obtained cord blood samples of 98 neonates (gestational age 25-42 weeks). In eight infants with bacterial infection, the mean percentage of L-selectin(high) lymphocytes was 32.5% (SD 20.1%), compared to 60.1% (SD 18.7%) in the control group (P < 0.01). A percentage of L-selectin(high) lymphocytes of less than 42% had a sensitivity of 75% and a specificity of 82% in identifying infected newborns. Cord blood lymphocyte L-selectin expression was independent of gestational age, birth weight, umbilical artery pH, hematocrit, white blood cell count, absolute neutrophil count, C-reactive protein level, or maternal fever before delivery while there was a weak correlation with the newborn's immature/total ratio and platelet count. To our knowledge, this is the first report demonstrating downregulation of human lymphocyte L-selectin expression following activation of the immune system in vivo.