Differing roles of CD1d2 and CD1d1 proteins in type I natural killer T cell development and function

MHC class I-like CD1 molecules have evolved to present lipid-based antigens to T cells. Differences in the antigen-binding clefts of the CD1 family members determine the conformation and size of the lipids that are presented, although the factors that shape CD1 diversity remain unclear. In mice, two homologous genes, CD1D1 and CD1D2, encode the CD1d protein, which is essential to the development and function of natural killer T (NKT) cells. However, it remains unclear whether both CD1d isoforms are equivalent in their antigen presentation capacity and functions. Here, we report that CD1d2 molecules are expressed in the thymus of some mouse strains, where they select functional type I NKT cells. Intriguingly, the T cell antigen receptor repertoire and phenotype of CD1d2-selected type I NKT cells in CD1D1−/− mice differed from CD1d1-selected type I NKT cells. The structures of CD1d2 in complex with endogenous lipids and a truncated acyl-chain analog of α-galactosylceramide revealed that its A′-pocket was restricted in size compared with CD1d1. Accordingly, CD1d2 molecules could not present glycolipid antigens with long acyl chains efficiently, favoring the presentation of short acyl chain antigens. These results indicate that the two CD1d molecules present different sets of self-antigen(s) in the mouse thymus, thereby impacting the development of invariant NKT cells

Novel role for STAT3 in transcriptional regulation of NK immune cell targeting receptor MICA on cancer cells.

International audienceThe role of natural killer group 2, member D receptor (NKG2D)-expressing natural killer (NK) cells in tumor immunosurveillance is now well established. Nevertheless, tumor progression occurs despite tumor immunosurveillance, leading to cancer persistence in immunocompetent hosts. STAT3 plays a pivotal role both in oncogenic functions and in immunosuppression. In this study, we investigated the role of STAT3 in suppressing NK cell-mediated immunosurveillance. Using a colorectal cancer cell line (HT29) that can poorly activate NK, we neutralized STAT3 with pharmacologic inhibitors or siRNA and found that this led to an increase in NK degranulation and IFN-γ production in a TGF-β1-independent manner. Exposure to NKG2D-neutralizing antibodies partially restored STAT3 activity, suggesting that it prevented NKG2D-mediated NK cell activation. On this basis, we investigated the expression of NKG2D ligands after STAT3 activation in HT29, mesenchymal stem cells, and activated lymphocytes. The NK cell recognition receptor MHC class I chain-related protein A (MICA) was upregulated following STAT3 neutralization, and a direct interaction between STAT3 and the MICA promoter was identified. Because cross-talk between DNA damage repair and NKG2D ligand expression has been shown, we assessed the influence of STAT3 on MICA expression under conditions of genotoxic stress. We found that STAT3 negatively regulated MICA expression after irradiation or heat shock, including in lymphocytes activated by CD3/CD28 ligation. Together, our findings reveal a novel role for STAT3 in NK cell immunosurveillance by modulating the MICA expression in cancer cells

Dendritic cell and natural killer cell cross-talk: a pivotal role of CX3CL1 in NK cytoskeleton organization and activation

Initial molecular events leading to natural killer lymphocyte (NK) and dendritic cell (DC) interactions are largely unknown. Here, the role of CX3CL1 (fractalkine), a chemokine expressed on mature dendritic cells (mDCs) has been investigated. We show that CX3CL1 promotes NK activation by mDCs. After blocking of CX3CL1 by antibody, no activation occurred but major histocompatibility complex (MHC) class I neutralization restored DC-mediated NK activation, suggesting an interaction between CX3CL1 signaling and the functioning of inhibitory KIR. Then the YTS NK cell line, in which the inhibitory receptor KIR2DL1 had been introduced, was used. The presence of KIR2DL1 did not decrease YTS activation by HLA-Cw4 DC when CX3CL1 was functional. In contrast, CX3CL1 neutralization led to killer cell immunoglobulin-like receptor (KIR) phosphorylation and SHP-1 recruitment in YTSKIR2DL1 cultured with HLA-Cw4 mDCs. Moreover, CX3CL1 neutralization promoted dispersion of lipid rafts and the formation of a multiprotein complex required for cytoskeletal rearrangements in YTS NK cells. These findings point to a pivotal role of CX3CL1 in the activation of resting NK cells by mature DCs

Association Between Early Invasive Mechanical Ventilation and Day-60 Mortality in Acute Hypoxemic Respiratory Failure Related to Coronavirus Disease-2019 Pneumonia

Objectives:. About 5% of patients with coronavirus disease-2019 are admitted to the ICU for acute hypoxemic respiratory failure. Opinions differ on whether invasive mechanical ventilation should be used as first-line therapy over noninvasive oxygen support. The aim of the study was to assess the effect of early invasive mechanical ventilation in coronavirus disease-2019 with acute hypoxemic respiratory failure on day-60 mortality. Design:. Multicenter prospective French observational study. Setting:. Eleven ICUs of the French OutcomeRea network. Patients:. Coronavirus disease-2019 patients with acute hypoxemic respiratory failure (Pao2/Fio2 ≤ 300 mm Hg), without shock or neurologic failure on ICU admission, and not referred from another ICU or intermediate care unit were included. Intervention:. We compared day-60 mortality in patients who were on invasive mechanical ventilation within the first 2 calendar days of the ICU stay (early invasive mechanical ventilation group) and those who were not (nonearly invasive mechanical ventilation group). We used a Cox proportional-hazard model weighted by inverse probability of early invasive mechanical ventilation to determine the risk of death at day 60. Measurement and Main Results:. The 245 patients included had a median (interquartile range) age of 61 years (52–69 yr), a Simplified Acute Physiology Score II score of 34 mm Hg (26–44 mm Hg), and a Pao2/Fio2 of 121 mm Hg (90–174 mm Hg). The rates of ICU-acquired pneumonia, bacteremia, and the ICU length of stay were significantly higher in the early (n = 117 [48%]) than in the nonearly invasive mechanical ventilation group (n = 128 [52%]), p < 0.01. Day-60 mortality was 42.7% and 21.9% in the early and nonearly invasive mechanical ventilation groups, respectively. The weighted model showed that early invasive mechanical ventilation increased the risk for day-60 mortality (weighted hazard ratio =1.74; 95% CI, 1.07–2.83, p=0.03). Conclusions:. In ICU patients admitted with coronavirus disease-2019-induced acute hypoxemic respiratory failure, early invasive mechanical ventilation was associated with an increased risk of day-60 mortality. This result needs to be confirmed

Life Support Limitations in Mechanically Ventilated Stroke Patients

Objectives:. The determinants of decisions to limit life support (withholding or withdrawal) in ventilated stroke patients have been evaluated mainly for patients with intracranial hemorrhages. We aimed to evaluate the frequency of life support limitations in ventilated ischemic and hemorrhagic stroke patients compared with a nonbrain-injured population and to determine factors associated with such decisions. Design:. Multicenter prospective French observational study. Setting:. Fourteen ICUs of the French OutcomeRea network. PATIENTS:. From 2005 to 2016, we included stroke patients and nonbrain-injured patients requiring invasive ventilation within 24 hours of ICU admission. INTERVENTION:. None. MEASUREMENTS AND MAIN RESULTS:. We identified 373 stroke patients (ischemic, n = 167 [45%]; hemorrhagic, n = 206 [55%]) and 5,683 nonbrain-injured patients. Decisions to limit life support were taken in 41% of ischemic stroke cases (vs nonbrain-injured patients, subdistribution hazard ratio, 3.59 [95% CI, 2.78–4.65]) and in 33% of hemorrhagic stroke cases (vs nonbrain-injured patients, subdistribution hazard ratio, 3.9 [95% CI, 2.97–5.11]). Time from ICU admission to the first limitation was longer in ischemic than in hemorrhagic stroke (5 [3–9] vs 2 d [1–6] d; p < 0.01). Limitation of life support preceded ICU death in 70% of ischemic strokes and 45% of hemorrhagic strokes (p < 0.01). Life support limitations in ischemic stroke were increased by a vertebrobasilar location (vs anterior circulation, subdistribution hazard ratio, 1.61 [95% CI, 1.01–2.59]) and a prestroke modified Rankin score greater than 2 (2.38 [1.27–4.55]). In hemorrhagic stroke, an age greater than 70 years (2.29 [1.43–3.69]) and a Glasgow Coma Scale score less than 8 (2.15 [1.08–4.3]) were associated with an increased risk of limitation, whereas a higher nonneurologic admission Sequential Organ Failure Assessment score was associated with a reduced risk (per point, 0.89 [0.82–0.97]). Conclusions:. In ventilated stroke patients, decisions to limit life support are more than three times more frequent than in nonbrain-injured patients, with different timing and associated risk factors between ischemic and hemorrhagic strokes