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

Abstract

Background: Thrombocytopenia is frequently associated with increased mortality in sepsis; however, the underlying immunological mechanisms remain poorly understood. 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 (HD), 27 non-thrombocytopenic (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^TM Green fluorescence and validated by MPO-DNA ELISA.

Results: TP patients showed higher percentages of PD-L1+ PLTs and increased CXCR4 expression on PLTs compared to N-TP patients. Their plasma also contained elevated sP-selectin and VEGF levels. Compared to HD, 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, NE, and S100A8/A9 levels. Clinically, TP patients had worse outcomes, with lower sCD40L levels and impaired in vitro extracellular DNA release correlating with disease severity (SOFA ≥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.