Impaired D-myo-Inositol 1,4,5-Triphosphate Generation from Cord Blood Polymorphonuclear Leukocytes

Abstract

D-myo-Inositol 1,4,5-triphosphate (IP,) 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 degranulation, which are typically depressed in newborn infants. IP, generation can be stimulated by N-formyl-methionyl-leucylphenylalanine (fMLP) tripeptide, which mimics the naturally occurring bacterial oligopeptides. In this study both neonatal and adult polymorphonuclear leukocytes were stimulated by fMLP (1 X lop6 M) and the levels of IP, were assayed by a specific radiometric method. The time course of IP, 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 [IP,] at the time peak of 10 s. As expected IP, generation was significantly (F test, p < 0.0001, n = 39) lower in newborns than in adults (means 2 SD = 0.64 + 0.25; 1.26 + 0.36, ng/106 cells, respectively). Besides soluble stimulus, neutrophils were treated with a particulate stimulus, namely serumtreated zymosan, which is also able to stimulate IP, synthesis from polymorphonuclear leukocytes. Serum-treated zymosan produced a prolonged elevation in the level of IP,, reaching a Human PMN are the first line of defense against nonviral infections. In response to an appropriate stimulus, they are able to diapedese through the endothelium and vessel wall in to the inflammatory focus killing and/or inactivating the invading organisms.Newborn infants show an increased susceptibility to serious and overwhelming bacterial and fungal infections. This leads to increased morbidity and mortality, in spite of advances in antibiotic therapy. Although abnormalities have been described in all compartments of the neonatal host defense system (I), FMLP is a synthetic tripeptide with structural and chemotactic characteristics similar to the naturally occurring bacterial oligopeptides (3). It is able to stimulate chemotaxis by binding to specific plasma membrane receptors of polymorphonuclear cells (4). The signal is transduced by the dissociation of the pertussis toxin-sensitive a-GTP complex from the heterotrimeric G protein and the consequent activation of a phospholipase C (5, 6). This, in turn, hydrolyzes PIP2 into two second messengers, namely DAG and IP,. The simultaneous generation of these two second messengers is responsible for activating a cascade of events that results in the cellular response. In particular, IP, is able to mobilize ca2+ from the intracellular