Acute lung injury (ALI) is the common and clinically severe complication of bacterial sepsis, and is markedly associated with adverse outcomes in intensive care units (ICUs) [1,2]. ALI is characterized by an intensified host-defense immune response, wherein a plethora of inflammatory cells infiltrate lung tissue [2]. Lung endothelial cells (ECs) are particularly susceptible to interference from circulating pathogens, bacterial byproducts, and cytokines. A compromised endothelial barrier can precipitate lung edema, an influx of neutrophils and macrophages, impaired coagulation function, and the release of inflammatory mediators. Collectively, these pathophysiological changes are directly implicated in the elevated mortality rates observed in sepsis-induced conditions [3,4].

Programmed Death Ligand 1 (PD-L1) is extensively expressed across a spectrum of hematopoietic and non-hematopoietic cells, including ECs and EpiCs in the lung [5]. Our previous study demonstrated that PD-L1 expression on pulmonary ECs or EpiCs was significantly augmented in mice with indirect ALI (iALI). Notably, the blockade of PD-L1 expression on ECs substantially mitigated lung injury development. Moreover, suppression of PD-L1 gene expression decreased monolayer permeability and preserved tight junction protein levels in cultured mouse endothelial cell lines [6]. Despite accumulating evidence underscoring the vital role of PD-L1 in modulating endothelial barrier function, the underlying intracellular signaling mechanisms remain largely unexplored.

NLRP3 is a member of the nucleotide-binding and oligomerization domain-like receptors (NLRs) family, which is categorized among pattern-recognition receptors (PRRs) that identify pathogen-associated molecular patterns (PAMPs). Inflammasomes serve as platforms for caspase-1 activation and the subsequent secretion of pro-inflammatory cytokines [7,8]. Upon activation, NLRP3 oligomerizes, showcasing clustered pyrin domains (PYD) that interact with the PYD domain of ASC, consequently facilitating caspase-1 activation exclusively associated with pyroptosis [9]. Recent studies have underscored the critical role of pyroptosis in the pathogenesis of lung injury, where pyroptosis induced by the NLRP3 inflammasome has been identified as a key contributor to endothelial dysfunction. Pharmacological interventions, such as statins and hypoglycemic agents, have been shown to enhance vascular function by inhibiting the inflammasome signaling pathway [10].

In this study, we aimed to elucidate the potential intracellular mechanisms responsible for PD-L1-mediated dysfunction in human lung microvascular endothelial cells (HMVECs). Concurrently, this study sought to extend our understanding of the role PD-L1 plays in the regulation of inflammasome activation and pyroptosis within a mouse model of indirect ALI.