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Impaired D-myo-inositol 1,4,5-triphosphate generation from cord blood polymorphonuclear leukocytes
P Santoro1, V Agosti, D Viggiano
1Department of Pediatrics, University Federico II, Naples, Italy.
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 degranulation, which are typically depressed in newborn infants. IP3 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 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/10(6) 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.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Newborns show reduced D-myo-inositol 1,4,5-triphosphate (IP3) generation in neutrophils compared to adults. This key second messenger regulates calcium levels, impacting immune cell functions. IP3 levels were significantly lower in neonatal cord blood samples after stimulation.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- D-myo-inositol 1,4,5-triphosphate (IP3) is a crucial second messenger regulating intracellular calcium levels in immune cells like neutrophils.
- In polymorphonuclear leukocytes (PMNs), elevated intracellular calcium ([Ca2+]) triggers essential functions such as adherence, aggregation, chemotaxis, and degranulation.
- These vital immune functions are often diminished in newborn infants.
Purpose of the Study:
- To investigate and compare IP3 generation levels in neonatal versus adult polymorphonuclear leukocytes.
- To assess the impact of specific stimuli on IP3 production in different age groups.
Main Methods:
- Human neonatal (cord blood) and adult PMNs were stimulated with N-formyl-methionyl-leucylphenylalanine (fMLP) at 1 x 10(-6) M.
- IP3 levels were quantified using a specific radiometric assay.
- Time course analysis of IP3 generation was performed up to 60 seconds, with a focus on peak response at 10 seconds.
Main Results:
- IP3 generation was significantly lower in neonatal PMNs compared to adult PMNs (0.64 ± 0.25 ng/10^6 cells vs. 1.26 ± 0.36 ng/10^6 cells, p < 0.0001).
- Stimulation with fMLP revealed a reduced IP3 response in cord blood samples.
- A particulate stimulus, serum-treated zymosan, induced a prolonged IP3 elevation in both neonatal and adult PMNs, reaching a plateau within 120 seconds.
Conclusions:
- Neonatal neutrophils exhibit a demonstrably reduced capacity for IP3 generation in response to fMLP stimulation compared to adult neutrophils.
- This impaired IP3 signaling in newborns may contribute to the observed depression of critical immune functions.
- Further research is warranted to understand the full implications of altered IP3 signaling in neonatal immunity.