Sepsis Induces a Dysregulated Neutrophil Phenotype That Is Associated with Increased Mortality

Abstract

Background Neutrophil dysfunction in sepsis has been implicated in the pathogenesis of multiorgan failure; however, the role of neutrophil extracellular traps (NETs) remains uncertain. We aimed to determine the sequential changes in ex vivo NETosis and its relationship with mortality in patients with sepsis and severe sepsis. Methods This was a prospective observational cohort study enrolling 21 healthy age-matched controls and 39 sepsis and 60 severe sepsis patients from acute admissions to two UK hospitals. Patients had sequential bloods for the ex vivo assessment of NETosis in response to phorbol-myristate acetate (PMA) using a fluorometric technique and chemotaxis using time-lapse video microscopy. Continuous data was tested for normality, with appropriate parametric and nonparametric tests, whilst categorical data was analysed using a chi-squared test. Correlations were performed using Spearman's rho. Results Ex vivo NETosis was reduced in patients with severe sepsis, compared to patients with sepsis and controls (p = 0.002). PMA NETosis from patients with septic shock was reduced further (p < 0.001) compared to controls. The degree of metabolic acidosis correlated with reduced NETosis (p < 0.001), and this was replicated when neutrophils from healthy donors were incubated in acidotic media. Reduced NETosis at baseline was associated with an increased 30-day (p = 0.002) and 90-day mortality (p = 0.014) in sepsis patients. These findings were accompanied by defects in neutrophil migration and delayed apoptosis. Resolution of sepsis was not associated with the return to baseline levels of NETosis or migration. Conclusions Sepsis induces significant changes in neutrophil function with the degree of dysfunction corresponding to the severity of the septic insult which persists beyond physiological recovery from sepsis. The changes induced lead to the failure to effectively contain and eliminate the invading pathogens and contribute to sepsis-induced immunosuppression. For the first time, we demonstrate that reduced ex vivo NETosis is associated with poorer outcomes from sepsis.

Neutrophil extracellular trap formation and nuclease activity in septic patients

“…In the aforementioned publications, all types of circulating DNAs contribute to the measured amount of cfDNA, which than was found to be increased in septic patients (10,11) or mice (8). Another work showed increased concentrations of cfDNA in patients with sepsis despite decreased NET release, which supports our argumentation (23).…”

“…shown by Patel et al, who measured NET release ex vivo in a cohort of septic patients comparable to our cohort (23). In fact, we included patients with septic shock, as all of them needed vasoactive medication.…”

DAMPs and NETs in Sepsis

“…Several studies have demonstrated that severe sepsis alters the neutrophil phenotype and hinders NETosis ex vivo (165, 166). However, it is not clear from these studies whether in vivo NET formation is impaired during sepsis.…”

The Diverse Function of PD-1/PD-L Pathway Beyond Cancer

“…Hotchkiss et al found that in septic patients, PD-1 expression on T cells was elevated, which was linked to poor proliferation of T cells as well as a high risk of secondary nosocomial infections and mortality (91). In addition, in septic shock patients, increased expression of PD-L1 in monocytes is correlated with 28-day mortality (Table 1) (92), and the abundance of PD-L1-expressing neutrophils is a marker of disease severity and predicts prognosis in sepsis (Table 1) (90, 148).…”