Identification and Characterization of Two Human Monocyte-Derived Dendritic Cell Subpopulations with Different Functions in Dying Cell Clearance and Different Patterns of Cell Death.

Human monocyte-derived dendritic cells (mdDCs) are versatile cells that are used widely for research and experimental therapies. Although different culture conditions can affect their characteristics, there are no known subpopulations. Since monocytes differentiate into dendritic cells (DCs) in a variety of tissues and contexts, we asked whether they can give rise to different subpopulations. In this work we set out to characterize two human mdDC subpopulations that we identified and termed small (DC-S) and large (DC-L). Morphologically, DC-L are larger, more granular and have a more complex cell membrane. Phenotypically, DC-L show higher expression of a wide panel of surface molecules and stronger responses to maturation stimuli. Transcriptomic analysis confirmed their separate identities and findings were consistent with the phenotypes observed. Although they show similar apoptotic cell uptake, DC-L have different capabilities for phagocytosis, demonstrate better antigen processing, and have significantly better necrotic cell uptake. These subpopulations also have different patterns of cell death, with DC-L presenting an inflammatory, "dangerous" phenotype while DC-S mostly downregulate their surface markers upon cell death. Apoptotic cells induce an immune-suppressed phenotype, which becomes more pronounced among DC-L, especially after the addition of lipopolysaccharide. We propose that these two subpopulations correspond to inflammatory (DC-L) and steady-state (DC-S) DC classes that have been previously described in mice and humans.

Therapy with eculizumab for patients with CD59 p.Cys89Tyr mutation.

OBJECTIVE: The objective of this work was to report on the outcome of eculizumab treatment in pediatric patients with recurrent acute predominantly motor, demyelinating neuropathy with conduction block, and chronic hemolysis attributed to p.Cys89Tyr mutation in the CD59 gene. METHODS: Four patients were recruited from our new registry of patients with homozygosity for the p.Cys89Tyr mutation on CD59. Participants received repeated intravenous eculizumab. In this 24-month open-label phase IIa study, we aimed to determine whether eculizumab reduces chronic hemolysis, and cumulative doses of steroids and intravenous immunoglobulin (IVIG), and ameliorates neurological deficits, compared to pretreatment status. Treatment response was evaluated every 2 to 4 weeks over 104 weeks and included examination with gross motor scoring by American Spinal Injury Association Impairment Scale and Inflammatory Neuropathy Cause and Treatment disability score, laboratory examination, well-being [12-item Short Form Health Survey; SF-12]). Neurological relapses and cumulative dose of IVIGs and/or corticosteroids before and after treatment were documented. Red blood cells (RBCs) and neutrophils were stained to evaluate C5b-9 deposition. ClinicalTrials.gov: NCT01579838. RESULTS: Dramatic and significant neurological amelioration in the upper limbs and trunk with more-modest amelioration in the lower limbs was observed in all patients. Corticosteroid and IVIG treatment was completely stopped. No patient relapsed during treatment despite infections, and there were no hospital admissions. Decreased C3bi and C5b-9 deposition on RBCs and neutrophils was documented (p < 0.0001). The SF-12 health questionnaires indicated significant improvement (p < 0.003). INTERPRETATION: Eculizumab was safely administered to these patients. Marked clinical improvement suggests that eculizumab may be a life-saving treatment for patients with acute predominantly motor, demyelinating neuropathy with conduction block, and secondary axonal damage attributed to primary p.Cys89Tyr mutation in the CD59 gene. Ann Neurol 2016;80:708-717.

Apoptotic cells induce NF-κB and inflammasome negative signaling.

As they undergo phagocytosis, most early apoptotic cells negatively regulate proinflammatory signaling and were suggested as a major mechanism in the resolution of inflammation. The dextran sulfate sodium model is generally viewed as an epithelial damage model suited to investigate innate immune responses. Macrophages primed with LPS and subsequently exposed to DSS secrete high levels of IL-1ß in an NLRP3-, ASC-, and caspase-1-dependent manner. The aim of this research was to test the therapeutic effect of a single dose of apoptotic cells in a DSS-colitis model and to explore possible mechanisms. Primary peritoneal macrophages, the DSS mice model, and Nlrp3-deficient mice, were used to assess the effect apoptotic cells on colitis. Immunohistochemistry, flow-cytometer, and western blots helped to explore the effect and mechanisms. Using a variety of NLRP3 triggering mechanisms, we show that apoptotic cells negatively regulate NF-κB and NLRP3 activation in primary peritoneal macrophages, at pre- and post-transcription levels, via inhibition of reactive oxygen species, lysosomal stabilization, and blocking K+ efflux. This property of apoptotic cells is demonstrated in a dramatic clinical, histological, and immunological amelioration of DSS colitis in Balb/c and B6 mice following a single administration of apoptotic cells.

Dissociation between mature phenotype and impaired transmigration in dendritic cells from heparanase-deficient mice.

To reach the lymphatics, migrating dendritic cells (DCs) need to interact with the extracellular matrix (ECM). Heparanase, a mammalian endo-ß-D-glucuronidase, specifically degrades heparan sulfate proteoglycans ubiquitously associated with the cell surface and ECM. The role of heparanase in the physiology of bone marrow-derived DCs was studied in mutant heparanase knock-out (Hpse-KO) mice. Immature DCs from Hpse-KO mice exhibited a more mature phenotype; however their transmigration was significantly delayed, but not completely abolished, most probably due to the observed upregulation of MMP-14 and CCR7. Despite their mature phenotype, uptake of beads was comparable and uptake of apoptotic cells was more efficient in DCs from Hpse-KO mice. Heparanase is an important enzyme for DC transmigration. Together with CCR7 and its ligands, and probably MMP-14, heparanase controls DC trafficking.

Constitutive neutrophil apoptosis: regulation by cell concentration via S100 A8/9 and the MEK-ERK pathway.

Programmed cell death (PCD) is a fundamental mechanism in tissue and cell homeostasis. It was long suggested that apoptosis regulates the cell number in diverse cell populations; however no clear mechanism was shown. Neutrophils are the short-lived, first-line defense of innate immunity, with an estimated t = 1/2 of 8 hours and a high turnover rate. Here we first show that spontaneous neutrophil constitutive PCD is regulated by cell concentrations. Using a proteomic approach, we identified the S100 A8/9 complex, which constitutes roughly 40% of cytosolic protein in neutrophils, as mediating this effect. We further demonstrate that it regulates cell survival via a signaling mechanism involving MEK-ERK via TLR4 and CD11B/CD18. This mechanism is suggested to have a fine-tuning role in regulating the neutrophil number in bone marrow, peripheral blood, and inflammatory sites.

What do we mean when we write "senescence," "apoptosis," "necrosis," or "clearance of dying cells"?

The clearance of dying cells has become an important field of research. Apart from a significant increase in our understanding of the mechanisms for uptake, cell clearance is a basic mechanism in tissue homeostasis, cancer, resolution of inflammation, induction of tolerance, and autoimmunity. Phagocytosis of dying cells is a complex process, involving many interacting molecules on the dying cell and the phagocyte, and in the microenvironment. Although much is known on the subject, there are many questions and unknown variables that remain under investigation. Naturally, different terms were developed, among which some are misused, leading sometimes to pseudoconflicts of understanding. Several receptors were described as "phosphatidylserine receptor: are they all equal?" We will revise terms such as apoptosis, primary and secondary necrosis, lysed cells, senescent cells, clearance of apoptotic cells, efferocytosis, and more. We will try to point out misnomers, misunderstandings, and contradictions, and to define a consensual vocabulary.

iC3b-opsonized apoptotic cells mediate a distinct anti-inflammatory response and transcriptional NF-kappaB-dependent blockade.

In recent years, it has become apparent that the removal of apoptotic cells by macrophages and DC is not only noninflammatory, but also immune-inhibitory, in most although not all circumstances. Complement may be involved in the uptake of apoptotic cells via direct binding of bridging factors in some physiological circumstances, by opsonization and engagement of the complement receptors. In the current study, we use a complement-dependent system of apoptotic cell clearance by human-derived macrophages and DC. Using a luciferase reporter gene and measuring immune response to non-opsonic zymosan, we show that iC3b-apoptotic cells induce NF-kappaB inhibition in response to zymosan and LPS at the nuclear translocation, transcriptional and post-transcriptional levels, leading to profound inhibition of proinflammatory cytokines. In addition, interaction with iC3b-opsonized apoptotic cells is characterized by macrophage secretion of IL-10 and lack of TGF-beta secretion. In conclusion, in cells with iC3b receptors, opsonized apoptotic cells mediate a distinct anti-inflammatory response and transcriptional NF-kappaB-dependent blockage.