Early immune dynamics during the initiation of fatal tularemia caused by Francisella tularensis infection remain unknown. Unto that end, we generated a transcriptomic map at single-cell resolution of the innate-like lymphocyte responses to F. tularensis live vaccine strain (LVS) infection of mice. We found that both interferon-γ (IFN-γ)-producing type 1 and interleukin-17 (IL-17)-producing type 3 innate-like lymphocytes expanded in the infected lungs. Natural killer (NK) and NKT cells drove the type 1 response, whereas mucosal-associated invariant T (MAIT) and γδ T cells drove the type 3 response. Furthermore, tularemia-like disease resistant NKT cell-deficient, Cd1d -/- mice accumulated more MAIT1 cells, MAIT17 cells, and cells with a hybrid phenotype between MAIT1 and MAIT17 cells than wild-type mice. Critically, adoptive transfer of LVS-activated MAIT cells from Cd1d -/- mice, which were enriched in MAIT17 cells, was sufficient to protect LVS-susceptible, immunodeficient RAG2 -/- mice from severe LVS infection-inflicted pathology. Collectively, our findings position MAIT cells as potential mediators of IL-17-dependent protection from pulmonary tularemia-like disease.
© 2025 The Author(s).

Leptospira interrogans is a bacterial species responsible for leptospirosis, a neglected worldwide zoonosis. Mice and rats are resistant and can become asymptomatic carriers, whereas humans and some other mammals may develop severe forms of leptospirosis. Uncommon among spirochetes, leptospires contain lipopolysaccharide (LPS) in their outer membrane. LPS is highly immunogenic and forms the basis for a large number of serovars. Vaccination with inactivated leptospires elicits a protective immunity, restricted to serovars with related LPS. This protection that lasts in mice, is not long lasting in humans and requires annual boosts. Leptospires are stealth pathogens that evade the complement system and some pattern recognition receptors from the Toll-like (TLR) and Nod-Like families, therefore limiting antibacterial defense. In macrophages, leptospires totally escape recognition by human TLR4, and escape the TRIF arm of the mouse TLR4 pathway. However, very little is known about the recognition and processing of leptospires by dendritic cells (DCs), although they are crucial cells linking innate and adaptive immunity. Here we tested the activation of primary DCs derived from human monocytes (MO-DCs) and mouse bone marrow (BM-DCs) 24h after stimulation with saprophytic or different pathogenic virulent or avirulent L. interrogans. We measured by flow cytometry the expression of DC-SIGN, a lectin involved in T-cell activation, co-stimulation molecules and MHC-II markers, and pro- and anti-inflammatory cytokines by ELISA. We found that exposure to leptospires, live or heat-killed, activated dendritic cells. However, pathogenic L. interrogans, especially from the Icterohaemorraghiae Verdun strain, triggered less marker upregulation and less cytokine production than the saprophytic Leptospira biflexa. In addition, we showed a better activation with avirulent leptospires, when compared to the virulent parental strains in murine BM-DCs. We did not observe this difference in human MO-DCs, suggesting a role for TLR4 in DC stimulation. Accordingly, using BM-DCs from transgenic deficient mice, we showed that virulent Icterohaemorraghiae and Manilae serovars dampened DC activation, at least partly, through the TLR4 and TRIF pathways. This work shows a novel bacterial immune evasion mechanism to limit DC activation and further illustrates the role of the leptospiral LPS as a virulence factor.
Copyright © 2022 Cagliero, Vernel-Pauillac, Murray, Adler, Matsui and Werts.

This study aimed to investigate the possible relationship between the two biomarkers presepsin and procalcitonin (PCT) and monocyte immune function, and to explore their combination in mortality prediction in the early stage of sepsis. A total of 198 patients with bacterial infection and diagnosed with sepsis and 40 healthy control subjects were included. Blood samples were collected on admission within 24 h. Plasma concentrations of presepsin and PCT were measured. Expression of monocyte surface CD14, programmed cell death receptor ligand-1 (PD-L1) and human leucocyte Ag (HLA)-DR were determined using flow cytometry. Levels of plasma presepsin and PCT were significantly higher under septic conditions, and increased with the progression of sepsis. Monocyte CD14 and HLA-DR expression were decreased, while PD-L1 was overexpressed in sepsis compared to control. Presepsin and PCT concentrations were positively correlated with Sequential Organ Failure Assessment score, Acute Physiology and Chronic Health Evaluation System II score and PD-L1, while they were negatively correlated with CD14 and HLA-DR. Presepsin plus monocyte HLA-DR mean fluorescence intensity had the highest prognostic value over other parameters alone or in combination. Presepsin and PCT had a weak correlation with monocyte dysfunction during early sepsis. The combination of presepsin and monocyte HLA-DR could help improve prognostic value.

Recent improvements in the flow cytometry technology allow the determination of the general immune status through the development of multicolor immunofluorescence panels. The one-tube multicolor flow cytometry assay (OTMA) that is presented here identifies 20 different, clinically relevant immune cell subsets and three common activation markers. Thereby, a comprehensive immune status that covers all major immune cells is easily obtained.The assay is suitable for every common three lasers and 10 color flow cytometer and includes the application of 15 different antibodies. Furthermore, the assay requires only 100 μL of EDTA-treated whole-blood and less than 40 min for sample preparation. By being easily adaptable to individual requirements and by additionally determining absolute cell counts, the assay is well-suited for translational research in clinical trials.

This study tests the hypothesis that circulating mononuclear cells expressing osteocalcin (OCN) and bone alkaline phosphatase (BAP) are associated with distinct plaque tissue components in patients with early coronary atherosclerosis.
Plaque characteristics implying vulnerability develop at the earliest stage of coronary atherosclerosis. Increasing evidence indicates that cells from the myeloid lineage might serve as important mediators of destabilization. Plaque burden and its components were assessed regarding their relationship to monocytes carrying both pro-inflammatory (CD14) and osteogenic surface markers OCN and BAP.
Twenty-three patients with angiographically non-obstructive coronary artery disease underwent coronary endothelial function assessment and virtual histology-intravascular ultrasound of the left coronary artery. Plaque composition was characterized in the total segment (TS) and in the target lesion (TL) containing the highest amount of plaque burden. Blood samples were collected simultaneously from the aorta and the coronary sinus. Circulating cell counts were then identified from each sample and a gradient across the coronary circulation was determined.
Circulating CD14+/BAP+/OCN+ monocytes correlate with the extent of necrotic core and calcification (r=0.53, p=0.010; r=0.55, p=0.006, respectively). Importantly, coronary retention of CD14+/OCN+ cells also correlates with the amount of necrotic core and calcification (r=0.61, p=0.003; r=0.61, p=0.003) respectively.
Our study links CD14+/BAP+/OCN+ monocytes to the pathologic remodeling of the coronary circulation and therefore associates these cells with plaque destabilization in patients with early coronary atherosclerosis.
Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.