A distinctive immunophenotypic signature in thrombocytopenic septic patients: platelet and neutrophil dysregulations as key contributors to disease severity.

[BACKGROUND] Thrombocytopenia is frequently associated with increased mortality in sepsis; however, the underlying immunological mechanisms remain poorly understood.

[OBJECTIVES] This study characterizes molecular and phenotypic changes associated with thrombocytopenia in sepsis, focusing on platelets (PLTs), neutrophils, and their interactions, and evaluates their contributions to poor outcomes.

[METHODS] Blood samples were collected from 19 healthy donors, 27 nonthrombocytopenic (N-TP) and 22 thrombocytopenic (TP) patients with community-acquired sepsis at baseline (diagnosis), and at 24, 48, and 72 hours after admission. Plasma levels of PLT-derived mediators and neutrophil surrogate markers were quantified by ELISA. PLT and neutrophil phenotypes and neutrophil degranulation were assessed by flow cytometry, while extracellular DNA release, as a surrogate approximation of NETosis, was measured by SYTOX Green fluorescence and validated by myeloperoxidase (MPO)-DNA ELISA.

[RESULTS] TP patients showed higher percentages of PD-L1 PLTs and increased CXCR4 expression on PLTs compared with N-TP patients. Their plasma also contained elevated soluble P-selectin and vascular endothelial growth factor levels. Compared with healthy donors, TP patients exhibited fewer neutrophil-PLT complexes; however, a greater proportion of these complexes were PD-L1 and expressed higher CXCR4 levels than those in N-TP patients. Despite reduced extracellular DNA release upon stimulation, TP patients had higher plasma MPO-DNA complexes and MPO, neutrophil elastase, and S100A8/A9 levels. Clinically, TP patients had worse outcomes, with lower soluble CD40L levels and impaired in vitro extracellular DNA release correlating with disease severity (Sequential Organ Failure Assessment score ≥8).

[CONCLUSIONS] Our findings suggest a distinct immune signature in TP septic patients, defined by enhanced PLT activation and neutrophil dysfunction, potentially contributing to poor prognosis.