Improved survival after induction of sepsis by cecal slurry in PD-1 knockout murine neonates

Abstract

Introduction Sepsis and the ensuing immune dysfunction, continues to be a major contributor to neonatal morbidity and mortality. Neonatal sepsis also is associated with profound immune dysfunction. We have recently identified a role for a family of co-inhibitory molecules that are altered in murine sepsis and in critically ill adult patients, which may be a target for development of novel therapies. There is, however, a paucity of data pertaining to the role of co-inhibitory check point proteins in the control and modulation of neonatal sepsis. Methods The cecal slurry (CS) model consists of harvesting the cecal contents of an adult wild type (Wt) male mouse and combining it with 5% dextrose to create a cecal slurry (CS) with a concentration of 80mg/ml (LD70 at 7 days). Neonatal mice (5–7 days of age) underwent intraperitoneal injection (IP) of the CS or IP of 0.9% saline for sham procedure (Sh). Wild Type (C57BL/6) or PD-1−/− mice were used. 7 day survival study was undertaken. Cytometric bead array was used for cytokine expression. Blood and peritoneal fluid was cultured for bacterial burden. Flow cytometry was used to assess the peritoneal cavity cell populations. Results There was no mortality following Sh in either WT or PD-1−/− pups. PD-1 markedly affected sepsis survival with significantly improved survival in the PD-1−/− pups (40% versus 80%; p<0.01). This survival improvement was not associated with any difference in bacterial clearance. The bacterial burden was equivalent between WT and PD-1−/− pups at 24 hours following CS. However, PD-1−/− pups did display an increased circulating cytokine response to the CS compared with WT, with increased expression of IL-6, IL-10 and TNF-α levels. Within the peritoneal cavity, sepsis induced an influx of neutrophils, a finding that was increased in PD-1−/− pups. Although the T-cell response was unaffected by PD-1, it was noted that CS induced a loss of peritoneal B-cells in WT, while the peritoneal B-cell population was preserved in PD-1−/− pups. Conclusion Our data suggests that the checkpoint protein, PD-1, plays an important role in controlling the immune response to sepsis in the neonate, ultimately affecting sepsis related mortality in this neonatal murine model of sepsis. Akin to adult studies, this data further emphasizes the potential therapeutic target for PD-1 across a spectrum of septic patients.

Up-regulation of BTLA expression in myeloid dendritic cells in neonatal sepsis associated with the treatment outcome and down-regulation of DC function

“…The newborn immune system is complicated by its immaturity, however, akin to adult counterparts, immune exhaustion and dysfunction also occurred in neonates [30]. Published studies have shown that co-inhibitory receptors, including PD-1, CTLA-4 and BTLA, are contributed to the progression of sepsis [20,[31][32][33][34]. Although these receptors were originally thought primarily to be inducers of anergy in lymphocytes, such as CD4 + T cells, increasing evidence verified that innate cell populations, including macrophages, monocytes and DCs, also appear to be induced to express co-inhibitory receptors, including BTLA, and the ligation of these receptors may have effects on them as well [20].…”

A novel role for coinhibitory receptors/checkpoint proteins in the immunopathology of sepsis

“…A similar observation was made on severely injured patients, where the expression of high PD-1 blood leukocyte levels was correlated with worsening physiological dysfunction (50). Furthermore, to the extent that these are simply the aberrations of the CLP model as applied in adult male mice, the importance of PD-1 on throughout the age spectrum has been demonstrated (51, 52). Work by Young et al (51), using a cecal slurry model, documented that PD-1 gene deficiency also confers a survival advantage in this model of polymicrobial sepsis in neonatal mice.…”

“…Furthermore, to the extent that these are simply the aberrations of the CLP model as applied in adult male mice, the importance of PD-1 on throughout the age spectrum has been demonstrated (51, 52). Work by Young et al (51), using a cecal slurry model, documented that PD-1 gene deficiency also confers a survival advantage in this model of polymicrobial sepsis in neonatal mice. Several studies have also shown a clear role for PD-1 in modulating the geriatric immune response to sepsis (53, 54).…”

Analysis of PD-1 expression in the monocyte subsets from non-septic and septic preterm neonates

“…In contrast, the study by Zhang et al [ 38 ] observed up-regulation of solely ligands for PD-1 (PD-L1), but not PD-1, on CD14 + MO in septic shock adult patients in comparison to healthy volunteers. The only study to evaluate PD-1 expression in neonatal sepsis was performed in PD-1 knockout murine neonates with sepsis caused by cecal slurry [ 39 ]; it showed improved survival of the septic PD-1 knockout mice in comparison with the wild-type. In general, it is assumed that increased activity of the PD1/PD-L1 system in sepsis could lead to depletion of the key cells, such as monocytes and T cells, necessary for proper response to infection, therefore impairing essential anti-microbial and regulatory activities [ 37 ].…”