Mouse strain differences in resident peritoneal cells: a flow cytometric analysis

Thermoneutrality and severe malaria: investigating the effect of warmer environmental temperatures on the inflammatory response and disease progression

Introduction

Most studies using murine disease models are conducted at housing temperatures (20 - 22°C) that are sub-optimal (ST) for mice, eliciting changes in metabolism and response to disease. Experiments performed at a thermoneutral temperature (TT; 28 - 31°C) have revealed an altered immune response to pathogens and experimental treatments in murine disease model that have implications for their translation to clinical research. How such conditions affect the inflammatory response to infection with Plasmodium berghei ANKA (PbA) and disease progression is unknown. We hypothesized that changes in environmental temperature modulate immune cells and modify host response to malaria disease. To test this hypothesis, we conducted experiments to determine: (1) the inflammatory response to malarial agents injection in a peritonitis model and (2) disease progression in PbA-infected mice at TT compared to ST.

Methods

In one study, acclimatized mice were injected intraperitoneally with native hemozoin (nHZ) or Leishmania at TT (28 - 31°C) or ST, and immune cells, cytokine, and extracellular vesicle (EV) profiles were determined from the peritoneal cavity (PEC) fluid. In another study, PbA-infected mice were monitored until end-point (i.e. experimental malaria score ≥4).

Results

We found that Leishmania injection resulted in decreased cell recruitment and higher phagocytosis of nHZ in mice housed at TT. We found 398 upregulated and 293 downregulated proinflammatory genes in mice injected with nHZ, at both temperatures. We report the presence of host-derived EVs never reported before in a murine parasitic murine model at both temperatures. We observed metabolic changes in mice housed at TT, but these did not result to noticeable changes in disease progression compared to ST.

Discussion

To our knowledge, these experiments are the first to investigate the effect of thermoneutrality on a malaria murine model. We found important metabolic difference in mice housed at TT. Our results offer insights on how thermoneutrality might impact a severe malaria murine model and directions for more targeted investigations.

Sterile Injury Repair and Adhesion Formation at Serosal Surfaces

Most multicellular organisms have a major body cavity containing vital organs. This cavity is lined by a mucosa-like serosal surface and filled with serous fluid which suspends many immune cells. Injuries affecting the major body cavity are potentially life-threatening. Here we summarize evidence that unique damage detection and repair mechanisms have evolved to ensure immediate and swift repair of injuries at serosal surfaces. Furthermore, thousands of patients undergo surgery within the abdominal and thoracic cavities each day. While these surgeries are potentially lifesaving, some patients will suffer complications due to inappropriate scar formation when wound healing at serosal surfaces defects. These scars called adhesions cause profound challenges for health care systems and patients. Therefore, reviewing the mechanisms of wound repair at serosal surfaces is of clinical importance. Serosal surfaces will be introduced with a short embryological and microanatomical perspective followed by a discussion of the mechanisms of damage recognition and initiation of sterile inflammation at serosal surfaces. Distinct immune cells populations are free floating within the coelomic (peritoneal) cavity and contribute towards damage recognition and initiation of wound repair. We will highlight the emerging role of resident cavity GATA6+ macrophages in repairing serosal injuries and compare serosal (mesothelial) injuries with injuries to the blood vessel walls. This allows to draw some parallels such as the critical role of the mesothelium in regulating fibrin deposition and how peritoneal macrophages can aggregate in a platelet-like fashion in response to sterile injury. Then, we discuss how serosal wound healing can go wrong, causing adhesions. The current pathogenetic understanding of and potential future therapeutic avenues against adhesions are discussed.

Mitochondrial genetics cooperate with nuclear genetics to selectively alter immune cell development/trafficking

The nuclear genome drives differences in immune cell populations and differentiation potentials, in part regulated by changes in metabolism. Despite this connection, the role of mitochondrial DNA (mtDNA) polymorphisms (SNP) in this process has not been examined. Using mitochondrial nuclear exchange (MNX) mice, we and others have shown that mtDNA strongly influences varying aspects of cell biology and disease. Based upon an established connection between mitochondria and immune cell polarization, we hypothesized that mtDNA SNP alter immune cell development, trafficking, and/or differentiation. Innate and adaptive immune cell populations were isolated and characterizated from the peritoneum and spleen. While most differences between mouse strains are regulated by nuclear DNA (nDNA), there are selective changes that are mediated by mtDNA differences (e.g., macrophage (CD11c) differentiation), These findings highlight how nuclear-mitochondrial crosstalk may alter pathology and physiology via regulation of specific components of the immune system.

An innovative immunotherapeutic strategy for ovarian cancer: CLEC10A and glycomimetic peptides

BACKGROUND

Receptors specific for the sugar N-acetylgalactosamine (GalNAc) include the human type II, C-type lectin receptor macrophage galactose-type lectin/C-type lectin receptor family member 10A (MGL/CLEC10A/CD301) that is expressed prominently by human peripheral immature dendritic cells, dendritic cells in the skin, alternatively-activated (M2a) macrophages, and to lesser extents by several other types of tissues. CLEC10A is an endocytic receptor on antigen-presenting cells and has been proposed to play an important role in maturation of dendritic cells and initiation of an immune response. In this study, we asked whether a peptide that binds in the GalNAc-binding site of CLEC10A would serve as an effective tool to activate an immune response against ovarian cancer.

METHODS

A 12-mer sequence emerged from a screen of a phage display library with a GalNAc-specific lectin. The peptide, designated svL4, and a shorter peptide consisting of the C-terminal 6 amino acids, designated sv6D, were synthesized as tetravalent structures based on a tri-lysine core. In silico and in vitro binding assays were developed to evaluate binding of the peptides to GalNAc-specific receptors. Endotoxin-negative peptide solutions were administered by subcutaneous injection and biological activity of the peptides was determined by secretion of cytokines and the response of peritoneal immune cells in mice. Anti-cancer activity was studied in a murine model of ovarian cancer.

RESULTS

The peptides bound to recombinant human CLEC10A with high avidity, with half-maximal binding in the low nanomolar range. Binding to the receptor was Ca²⁺-dependent. Subcutaneous injection of low doses of peptides into mice on alternate days resulted in several-fold expansion of populations of mature immune cells within the peritoneal cavity. Peptide sv6D effectively suppressed development of ascites in a murine ovarian cancer model as a monotherapy and in combination with the chemotherapeutic drug paclitaxel or the immunotherapeutic antibody against the receptor PD-1. Toxicity, including antigenicity and release of cytotoxic levels of cytokines, was not observed.

CONCLUSION

sv6D is a functional ligand for CLEC10A and induces maturation of immune cells in the peritoneal cavity. The peptide caused a highly significant extension of survival of mice with implanted ovarian cancer cells with a favorable toxicity and non-antigenic profile.

Peritoneal T lymphocyte regulation by macrophages

The T cell composition of the peritoneal cavity (PerC) in naïve BALB/c, C57BL/6, DBA/2J, and B-1 B cell-defective BALB.xid mice was investigated. The BALB.xid PerC T cell pool had a high CD4:CD8 T cell ratio relative to the other strains whose ratios were similar to those found in their lymph node and spleen. All mice had significant representation of T cells with an activated (CD25(+), GITR(hi), CD44(hi), CD45RB(lo), CD62L(lo)) phenotype and low numbers of Foxp3(+) T(reg) cells in their PerC. Despite a phenotype indicative of activation, peritoneal T cell responses to CD3 ligation were very low for C57BL/6 and BALB.xid, but not BALB/c, mice. Enzyme inhibition and cytokine neutralization studies revealed active suppression of the T cell response mediated by the macrophages that represent a significant portion of PerC leucocytes. Driven by IFNγ to express iNOS, macrophages suppressed T cell activation in vitro by arginine catabolism. Although BALB/c T cells were also in a macrophage-dense environment their limited IFNγ production failed to trigger suppression. This difference between BALB/c and BALB.xid PerC T cells suggests a role for xid in shaping macrophage-mediated immune regulation.

Elevated mitochondrial reactive oxygen species generation affects the immune response via hypoxia-inducible factor-1alpha in long-lived Mclk1+/- mouse mutants

Mitochondrial reactive oxygen species (ROS) are believed to stabilize hypoxia-inducible factor (HIF)-1alpha, a transcriptional regulator of the immune response. Mclk1 encodes a mitochondrial protein that is necessary for ubiquinone biosynthesis. Heterozygote Mclk1(+/-) mutant mice are long-lived despite increased mitochondrial ROS and decreased energy metabolism. In this study, Mclk1(+/-) mutant mice in the C57BL/6J background displayed increased basal and induced expression of HIF-1alpha in liver and macrophages in association with elevated expression of inflammatory cytokines, in particular TNF-alpha. Mutant macrophages showed increased classical and decreased alternative activation, and mutant mice were hypersensitive to LPS. Consistent with these observations in vivo, knock-down of Mclk1 in murine RAW264.7 macrophage-like cells induced increased mitochondrial ROS as well as elevated expression of HIF-1alpha and secretion of TNF-alpha. We used an antioxidant peptide targeted to mitochondria to show that altered ROS metabolism is necessary for the enhanced expression of HIF-1alpha, which, in turn, is necessary for increased TNF-alpha secretion. These findings provide in vivo evidence for the action of mitochondrial ROS on HIF-1alpha activity and demonstrate that changes in mitochondrial function within physiologically tolerable limits modulate the immune response. Our results further suggest that altered immune function through a limited increase in HIF-1alpha expression can positively impact animal longevity.

Early vascular permeability in murine experimental peritonitis is co-mediated by resident peritoneal macrophages and mast cells: crucial involvement of macrophage-derived cysteinyl-leukotrienes

The initial phase of zymosan-induced peritonitis involves an increase of vascular permeability (peak at 30 min) that is correlated with high levels of vasoactive eicosanoids, namely, prostaglandins (PGI2 and PGE2) of cyclooxygenase-1 origin (as estimated by RT-PCR) and cysteinyl-leukotrienes. Previously, we showed that the increase of vascular permeability can be attributed only partially to mast cells and their histamine, as seen in mast cell-deficient WBB6F1-W/Wv mice. Thus we aimed to identify the major cellular source(s) that mediate vasopermeability, as well as particular vasoactive mediators operating in this model. For this purpose, some mice were selectively depleted of either peritoneal macrophages or mast cells, and/or they were treated with several pharmacologic inhibitors of cyclooxygenase- and lipoxygenase-metabolic pathways. More-over, macrophage-depleted mast cell-deficient WBB6F1-W/Wv mice and their controls (+/+) were used. The macrophage depletion always caused a profound decrease of both vascular permeability and lipid-mediator levels, which was particularly pronounced for leukotrienes, whereas the effects of mast-cell depletion were less severe. The macrophage/mast-cell co-mediation of vasopermeability was also revealed in thioglycolate-induced peritonitis, as well as the macrophage origin of cysteinyl-leukotrienes. Taken together, these findings demonstrate that the resident peritoneal macrophages are in fact the main contributors to the vasopermeability at the early stages of zymosan-induced peritonitis.