Survival and pulmonary injury after neonatal sepsis: PD-1:PD-L1’s contributions to mouse and human immunopathology.
Author(s):
Eleanor Fallon; Daithi Heffernan; Monique De Paepe; Chun-Shiang Chung; Alfred Ayala
Background:
Morbidity associated with neonatal sepsis remains a healthcare crisis. We recently demonstrated survival advantage of PD-1-/- mice following sepsis(80%) compared to wildtype counterparts(40%). We also demonstrated that 24hrs post-CS induced neutrophil influx, increased IL-6, IL-10 and TNF-α expression, all of which were attenuated among PD-1-/- mice. A clear role for these changes and their temporal significance has yet to be elucidated.
Hypothesis:
Indices of indirect acute lung injury and overall mortality will be attenuated across all time points in the setting of PD-1 and/or PD-L1 gene deletion. Further, lung tissue derived from human neonates who succumbed to sepsis will express increased levels of PD-1 and/or PD-L1.
Methods:
Polymicrobial infection was induced by intra-peritoneal injection of CS into C57BL/6, PD-1-/-, and PD-L1-/- neonatal mice. Lungs were harvested at 4, 12 and 24hrs. Survival analysis included q6hr checks for the 1st 48hrs followed by daily checks thereafter. Cytokine/chemokine and MPO assays were conducted, and pulmonary edema(PE) was measured by wet:dry ratio. Cultured pulmonary endothelial cells(ECs) were immunofluorescently(IF) stained for adhesion molecules. With IRB approval, human neonatal lung autopsy tissue was obtained and immunostained for PD-1 and PD-L1.
Results:
Unlike at 24hrs (where PE, MPO and several cytokines/chemokines were markedly increased), at 4hrs(n=3-10/group) and 12 hrs(n=3-6/group), there was no marked difference between sham and CS mice in terms of PE or MPO expression; and while cytokine/chemokine analysis revealed a trend toward increased IL-6 and KC after CS, this did not reach significance. Like PD-1-/- mice, survival analysis(n=29) of PD-L1-/- neonatal mice after CS resulted in 72% survival. On IF, zona occludens-1(ZO-1) cellular habitation shifted from membranous to peri-nuclear after CS in wildtype murine cultured ECs at 24hrs, but remained membranous among PD-1-/- lungs. Finally, assessment of human neonatal lungs(n=20) showed consistently more PD-1 expression in septic patients; this difference was not noted for PD-L1 expression.
Conclusions:
PD-1:PD-L1 ligation affects lung injury, but akin to experimentally septic adult mice, also affects murine survival after polymicrobial insult. This is echoed in part by septic human neonatal histology documenting increased pulmonary PD-1 levels. Together, these data suggest that aberrant signaling through the PD-1:PD-L1 pathway may be a viable therapeutic target in the septic neonate.