IMPAIRED D-MYO-INOSITOL 1,4,5-TRIPHOSPHATE GENERATION FROM CORD-BLOODPOLYMORPHONUCLEAR LEUKOCYTES

D-myo-Inositol 1,4,5-triphosphate (IP3) is a key second messenger in m any cells, including macrophages, T and B cells, and neutrophils, in w hich it regulates free intracellular calcium ion levels. In human poly morphonuclear leukocytes the rise of intracellular [Ca2+] is the signa l that activates a number of functions such as adherence, aggregation, chemotaxis, and degranulation, which are typically depressed in newbo rn infants. IP3 generation can be stimulated by N-formyl-methionyl-leu cylphenylalanine (fMLP) tripeptide, which mimics the naturally occurri ng bacterial oligopeptides. In this study both neonatal and adult poly morphonuclear leukocytes were stimulated by fMLP (1 x 10(-6) M) and th e levels of IP3 were assayed by a specific radiometric method. The tim e 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 conf irm this observation, we extended our study to a larger number of samp les, quantitating [IP3] at the time peak of 10 s. As expected IP3 gene ration was significantly (F test, p < 0.0001, n = 39) lower in newborn s than in adults (means +/- SD = 0.64 +/- 0.25; 1.26 +/- 0.36, ng/10(6 ) cells, respectively). Besides soluble stimulus, neutrophils were tre ated with a particulate stimulus, namely serum-treated zymosan, which is also able to stimulate IP3 synthesis from polymorphonuclear leukocy tes. Serum-treated zymosan produced a prolonged elevation in the level of IP3, reaching a plateau within 120 s in both cord blood and in con trol 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 a dult preparations (mean +/- SD = 1.09 +/- 0.45; 2.54 +/- 0.55, ng/10(6 ) cells, respectively). These data suggest that an impaired synthesis of IP3 is involved in the defective signal transduction of neonatal po lymorphonuclear leukocytes and could represent an important biochemica l mechanism behind the defective functions of neonatal neutrophils.