Programmed Cell Death Receptor-1 (PD-1)'s Effects on Innate Immune Cells: Unraveling Lung Injury After Neonatal Intra-abdominal Sepsis
*Eleanor A. Fallon, Daithi S. Heffernan, *Anne-Lise Rossi, *Chun-Shiang Chung, *Alfred Ayala
Brown University/Rhode Island Hospital, Providence, RI
Objective: To establish the role Programmed cell death receoptor-1 (PD-1) and its ligands on immunomodulation of lung injury after neonatal sepsis.
Design: Mice randomized to sham or cecal slurry (CS).
Patients: Mice: WT C57BL/6 or PD-1-/-, PD-L1-/-, PD-L2-/- on C57BL/6 background.
Interventions: Sham injection of normal saline. Cecal Slurry injection of cecal contents from an adult male WT donor to model intra-peritoneal, polymicrobial sepsis.
Main Outcome Measures: Lungs harvested after 24 hours were assessed via flow cytometry for neutrophils(CD11b+Ly6G+) and PD-1/PD-L1(Programmed Death Ligand 1)/PD-L2 presence. ELISA for pulmonary cytokines IL-6/IL-10/TNF-α.
Results: Consistent with previous findings on immunohistochemistry, we observed neutrophil influx following CS among WT lungs(p=0.0012), a phenomenon markedly attenuated in PD-1’s absence(p=0.0733). Although absolute number of neutrophils expressing PD-1, PD-L1 or PD-L2 significantly increased after CS vs. Sham(p=0.0031, 0.0018, 0.009 respectively), the percentage of distribution remained unchanged. Among PD-1-/- mice, however, expression of PD-L1 and PD-L2 was not upregulated either proportionally or among total cell counts, suggesting that PD-1’s ligand interactions regulate neutrophil influx into and habitation within pulmonary parenchyma. In WT, CS induced a relative increase(1.98(IQR 0.82-4.89)) of IL-6 over Sham vs. a relative decrease among PD-1-/- lungs(0.29(IQR=0.15-0.9;p=0.032); IL-10 echoed this relationship among WT(2.6(IQR 2.1-5.4)) vs. PD-1-/- lungs(0.57(IQR0.25-0.59;p=0.03)). There was no significant alteration of TNF-α expression across Naïve, Sham or CS lungs in either WT or PD-1-/- strains.
Conclusions: PD-1 and PD-L1 are current therapeutic targets against malignancy and could be future targets in sepsis. PD-1 affects the innate immune system, as represented by neutrophils, which may predominate over lymphocytes in this early post-natal stage of immune development in response to septic challenge.