Neonatal Platelets Induce Monocytes to a Myeloid-Derived Suppressor Cell Phenotype.

Area of Science:

• Immunology
• Neonatal Medicine
• Hematology

Background:

• Adult and neonatal platelets differ in immune molecule expression.
• Predicting platelet-immune cell interactions in neonates is complex due to varying factors.
• Previous studies showed adult, but not neonatal, platelet transfusions increased monocyte trafficking in neonatal mice.

Purpose of the Study:

• To investigate the distinct immune effects of neonatal versus adult platelets on monocytes.
• To determine the mechanism by which neonatal platelets influence T-cell activation.
• To explore the implications of these findings for neonatal platelet transfusions.

Main Methods:

• Incubation of monocytes with neonatal or adult platelets/releasates.
• Assessment of monocyte phenotype (e.g., PD-L1 expression) and T-cell activation in vitro.
• In vivo studies using a neonatal mouse model and an asthma-like model.
• Analysis of prostaglandin E2 (PGE2) and EP4 signaling pathways.

Main Results:

• Neonatal platelets, but not adult platelets, induced a myeloid-derived suppressor cell (MDSC) phenotype in monocytes.
• MDSCs generated by neonatal platelets exhibited increased PD-L1 expression.
• Monocytes pre-incubated with neonatal platelets or releasates suppressed T-cell activation both in vitro and in vivo.
• Neonatal platelet-induced immune suppression was mediated by increased PGE2 production signaling through monocyte EP4 receptors.

Conclusions:

• Neonatal platelets possess immune-limiting functions in the neonatal period by suppressing T-cell responses indirectly.
• These findings suggest a mechanism contributing to adverse outcomes observed with neonatal platelet transfusions.
• Understanding these distinct platelet functions is crucial for optimizing neonatal care.