Impaired D-myo-inositol 1,4,5-triphosphate generation from cord blood polymorphonuclear leukocytes

Abstract

D-myo-Inositol 1,4,5-triphosphate (IP3) is a key second messenger in many cells, including macrophages, T and B cells, and neutrophils, in which it regulates free intracellular calcium ion levels. In human polymorphonuclear leukocytes the rise of intracellular [Ca2+] is the signal that activates a number of functions such as adherence, aggregation, chemotaxis, and degranu-lation, which are typically depressed in newborn infants. IP3 generation can be stimulated by Af-formyl-methionyl-leucyl-phenylalanine (fMLP) tripeptide, which mimics the naturally occurring bacterial oligopeptides. In this study both neonatal and adult polymorphonuclear leukocytes were stimulated by fMLP (1 X 10-6 M) and the levels of IP3 were assayed by a specific radiometric method. The time course of IP3 generation was studied for up to 60 s in a total of 10 samples. The response appeared reduced in cord blood samples. To confirm this observation, we extended our study to a larger number of samples, quantitating [IP3] at the time peak of 10 s. As expected IP3 generation was significantly (F test, p < 0.0001, n = 39) lower in newborns than in adults (means ± SD = 0.64 ± 0.25; 1.26 ± 0.36, ng/106 cells, respectively). Besides soluble stimulus, neutrophils were treated with a particulate stimulus, namely serum-treated zymosan, which is also able to stimulate IP3 synthesis from polymorphonuclear leukocytes. Serum-treated zymosan produced a prolonged elevation in the level of IP3, reaching a plateau within 120 s in both cord blood and in control samples. At the 120-s time point significantly (F test, p < 0.002, n = 10) lower amounts of IP3 were found in newborn samples than in adult preparations (mean ± SD = 1.09 ± 0.45; 2.54 ± 0.55, ng/106 cells, respectively). These data suggest that an impaired synthesis of IP3 is involved in the defective signal transduction of neonatal polymorphonuclear leukocytes and could represent an important biochemical mechanism behind the defective functions of neonatal neutrophils. © 1995 International Pediatric Research Foundation, Inc.