Neonatal Platelets Differentiate Monocytes to a Myeloid Derived Suppressor Cell Phenotype

Area of Science:

• Immunology
• Neonatal Biology
• 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 platelet transfusion increased monocyte trafficking in neonatal mice.

Purpose of the Study:

• To investigate the immunomodulatory effects of neonatal versus adult platelets on monocytes.
• To determine if neonatal platelets induce a specific immune-suppressive phenotype in monocytes.
• To explore the mechanisms and in vivo relevance of these platelet-monocyte interactions.

Main Methods:

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

Main Results:

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

Conclusions:

• Neonatal platelets possess immune-limiting functions by indirectly suppressing T-cell responses via monocyte modulation.
• These findings suggest a potential mechanism contributing to adverse outcomes observed with neonatal platelet transfusions.
• Understanding these differences is crucial for optimizing neonatal care and transfusion strategies.