The prognostic impact of SIGLEC5-induced impairment of CD8+ T cell activation in sepsis

BACKGROUND

Sepsis is associated with T-cell exhaustion, which significantly reduces patient outcomes. Therefore, targeting of immune checkpoints (ICs) is deemed necessary for effective sepsis management. Here, we evaluated the role of SIGLEC5 as an IC ligand and explored its potential as a biomarker for sepsis.

METHODS

In vitro and in vivo assays were conducted to both analyse SIGLEC5's role as an IC ligand, as well as assess its impact on survival in sepsis. A multicentre prospective cohort study was conducted to evaluate the plasmatic soluble SIGLEC5 (sSIGLEC5) as a mortality predictor in the first 60 days after admission in sepsis patients. Recruitment included sepsis patients (n = 346), controls with systemic inflammatory response syndrome (n = 80), aneurism (n = 11), stroke (n = 16), and healthy volunteers (HVs, n = 100).

FINDINGS

SIGLEC5 expression on monocytes was increased by HIF1α and was higher in septic patients than in healthy volunteers after ex vivo LPS challenge. Furthermore, SIGLEC5-PSGL1 interaction inhibited CD8+ T-cell proliferation. Administration of sSIGLEC5r (0.8 mg/kg) had adverse effects in mouse endotoxemia models. Additionally, plasma sSIGLEC5 levels of septic patients were higher than HVs and ROC analysis revealed it as a mortality marker with an AUC of 0.713 (95% CI, 0.656-0.769; p < 0.0001). Kaplan-Meier survival curve showed a significant decrease in survival above the calculated cut-off (HR of 3.418, 95% CI, 2.380-4.907, p < 0.0001 by log-rank test) estimated by Youden Index (523.6 ng/mL).

INTERPRETATION

SIGLEC5 displays the hallmarks of an IC ligand, and plasma levels of sSIGLEC5 have been linked with increased mortality in septic patients.

FUNDING

Instituto de Salud Carlos III (ISCIII) and "Fondos FEDER" to ELC (PIE15/00065, PI18/00148, PI14/01234, PI21/00869), CDF (PI21/01178), RLR (FI19/00334) and JAO (CD21/00059).

Thiosulfinate-Enriched Allium sativum Extract Exhibits Differential Effects between Healthy and Sepsis Patients: The Implication of HIF-1α

Garlic (Allium sativum) has historically been associated with antioxidant, immunomodulatory, and microbiocidal properties, mainly due to its richness in thiosulfates and sulfur-containing phytoconstituents. Sepsis patients could benefit from these properties because it involves both inflammatory and refractory processes. We evaluated the effects of thiosulfinate-enriched Allium sativum extract (TASE) on the immune response to bacterial lipopolysaccharide (LPS) by monocytes from healthy volunteers (HVs) and patients with sepsis. We also explored the TASE effects in HIF-1α, described as the key transcription factor leading to endotoxin tolerance in sepsis monocytes through IRAK-M expression. Our results showed TASE reduced the LPS-triggered reactive oxygen species (ROS) production in monocytes from both patients with sepsis and HVs. Moreover, this extract significantly reduced tumor necrosis factor (TNF)-α, interleukin-1β, and interleukin-6 production in LPS-stimulated monocytes from HVs. However, TASE enhanced the inflammatory response in monocytes from patients with sepsis along with increased expression of human leukocyte antigen-DR. Curiously, these dual effects of TASE on immune response were also found when the HV cohort was divided into low- and high-LPS responders. Although TASE enhanced TNFα production in the LPS-low responders, it decreased the inflammatory response in the LPS-high responders. Furthermore, TASE decreased the HIF-1α pathway-associated genes IRAK-M, VEGFA and PD-L1 in sepsis cells, suggesting HIF-1α inhibition by TASE leads to higher cytokine production in these cells as a consequence of IRAK-M downregulation. The suppression of this pathway by TASE was confirmed in vitro with the prolyl hydroxylase inhibitor dimethyloxalylglycine. Our data revealed TASE’s dual effect on monocyte response according to status/phenotype and suggested the HIF-1α suppression as the possible underlying mechanism.

Cellular and humoral functional responses after BNT162b2 mRNA vaccination differ longitudinally between naive and subjects recovered from COVID-19

We have analyzed BNT162b2 vaccine-induced immune responses in naive subjects and individuals recovered from coronavirus disease 2019 (COVID-19), both soon after (14 days) and later after (almost 8 months) vaccination. Plasma spike (S)-specific immunoglobulins peak after one vaccine shot in individuals recovered from COVID-19, while a second dose is needed in naive subjects, although the latter group shows reduced levels all along the analyzed period. Despite how the neutralization capacity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mirrors this behavior early after vaccination, both groups show comparable neutralizing antibodies and S-specific B cell levels late post-vaccination. When studying cellular responses, naive individuals exhibit higher SARS-CoV-2-specific cytokine production, CD4+ T cell activation, and proliferation than do individuals recovered from COVID-19, with patent inverse correlations between humoral and cellular variables early post-vaccination. However, almost 8 months post-vaccination, SARS-CoV-2-specific responses are comparable between both groups. Our data indicate that a previous history of COVID-19 differentially determines the functional T and B cell-mediated responses to BNT162b2 vaccination over time.

SARS-CoV-2 Proteins Induce Endotoxin Tolerance Hallmarks: A Demonstration in Patients with COVID-19

According to a large number of reported cohorts, sepsis has been observed in nearly all deceased patients with COVID-19. We and others have described sepsis, among other pathologies, to be an endotoxin tolerance (ET)-related disease. In this study, we demonstrate that the culture of human blood cells from healthy volunteers in the presence of SARS-CoV-2 proteins induced ET hallmarks, including impairment of proinflammatory cytokine production, low MHC class II (HLA-DR) expression, poor T cell proliferation, and enhancing of both phagocytosis and tissue remodeling. Moreover, we report the presence of SARS-CoV-2 blood circulating proteins in patients with COVID-19 and how these levels correlate with an ET status, the viral RNA presence of SARS-CoV-2 in plasma, as well as with an increase in the proportion of patients with secondary infections.