Programmed Cell Death Receptor Ligand 1 Modulates the Regulatory T Cells’ Capacity to Repress Shock/Sepsis–Induced Indirect Acute Lung Injury by Recruiting Phosphatase Src Homology Region 2 Domain-Containing Phosphatase 1

Abstract

We recently reported that adoptively transferred (AT) exogenous CD4+CD25+ regulatory T cells (Tregs) to wild type (WT) mice can directly act to repress shock/sepsis induced experimental iALI and this is mediated in part by programmed cell death receptor 1 (PD-1). In this study, we further determine whether recipient mouse lacking PD-L1, one of the primary ligands for PD-1, contributes to the manipulation of the Tregs’ capacity to repress lung injury. To do this, Tregs isolated from the spleen of WT mice were AT into PD-L1−/− mice subjected to hemorrhagic shock [Hem] and subsequent to cecal ligation and puncture (CLP) to induce iALI. Samples were collected for analyses 24 hours after CLP. We found that in PD-L1−/− recipient mice, AT WT-Tregs lost the ability to reverse the development of iALI seen in WT recipient mice (i.e., no reduction of lung injury indices assessed by histology and vascular leakage; failure to decrease the lung neutrophil influx [MPO activity] or the rise in lung apoptosis [caspase 3 activity]). Also a significant increase of interlukin-1β (IL-1β) and keratinocyte-derived chemokine (KC), but no changes in IL-6, IL-10 and IL-17A levels in lung tissues were seen in these mice compared with iALI mice without AT of Tregs. Furthermore, we noted that the lung tissue tyrosine phosphatase Src homology region 2 domain-containing phosphatase 1 (SHP-1), but not SHP-2, was activated with the AT of Tregs in PD-L1−/− iALI mice. Finally, through local depletion of CD4+ T cells or CD25+ (Tregs) in the lung, prior to inducing iALI, we found that SHP-1 activation was associated with the loss of Tregs’ protective effects in vivo. Collectively, our data reveal that PD-L1 is a critical modulator of Treg’s ability to suppress iALI and this appears to involve SHP-1 activation.

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

“…Subsequently, Tang et al expanded the significance of PD-1:PD-L1 ligation on Tregs on mediating lung-protective effects by documenting that AT transfer of WT donor Tregs into PD-L1 gene deficient recipient mice did not confer protection against lung injury/inflammation. Further, the ligation PD-1:PD-L1 in this system also appears to preferentially signal through SHP-1 as opposed to SHP-2, similar to that reported above for septic patient T cells (91, 92). …”

“…Further, the ligation PD-1:PD-L1 in this system also appears to preferentially signal through SHP-1 as opposed to SHP-2, similar to that reported above for septic patient T cells. 91,92 La et al 93 to exhibit increased PD-1 expression in response to CLP. 47,95 This up-regulation of PD-1, from a naïve state of nearly undetectable levels, was also a little surprising as a number of groups had indicated that tissue macrophages did not express elevated levels of PD-1 typically.…”

Enhanced Innate Inflammation Induced by Anti-BTLA Antibody in Dual Insult Model of Hemorrhagic Shock/Sepsis

“…Non-lethal, fixed-pressure hemorrhagic shock was produced as previously described (24) (25) (26). In brief, following randomization to either Sham group or Hem group, mice were anesthetized using isoflurane.…”

“…Polymicrobial sepsis (CLP) was produced as previously described (24) (25) (26). In brief, 24 hours post Hem (or sham Hem), mice were anesthetized with isoflurane and a midline incision was made in the abdomen.…”

“…Hamster IgG (BioXcell) was administered as an isotype control. This was done since the model used here produces both a period of leukocyte/ non-immune cell ‘priming’ by exposure to hemorrhagic shock, followed by a “trigger” insult in the form of CLP that precipitates the development of acute lung injury along with other forms of multiple organ injury (24) (25) (26), we wanted to block the contributions of both events in our study.…”