Cholesterol in negatively charged lipid bilayers modulates the effect of the antimicrobial protein granulysin

Structural Engineering of Cationic Block Copolymer Architectures for Selective Breaching of Prokaryotic and Eukaryotic Biological Species

Positively charged antimicrobial polymers are known to cause severe damage to biological systems, and thus synthetic strategies are urgently required to design next-generation nontoxic cationic macromolecular architectures for healthcare applications. Here, we report a structural-engineering strategy to build cationic linear and star-block copolymer nanoarchitectures having identical chemical composition, molar mass, nanoparticle size, and positive surface charge, yet they differ distinctly in their biological action in breaching prokaryotic species such as E. coli (Gram-negative bacteria) without affecting eukaryotic species like red-blood and mammalian cells. For this purpose, linear and star-block structures are built on a polycaprolactone biodegradable platform having an imidazolium positive handle. Under physiological conditions, the linear architecture exhibits toxicity indiscriminately to all biological species, whereas its star counterpart is remarkably selective in membrane breaching action toward bacteria while maintaining inertness toward eukaryotic species. Confocal microscopy analysis of HPTS fluorescent dye-loaded star-polymer nanoparticles substantiated their antimicrobial action in E. coli. Tissue-penetrable near-infrared fluorescent dye (IR-780) loaded NP aided the in vivo biodistribution analysis and ex vivo quantification of cationic species' accumulations in vital organs in mice. Azithromycin, a clinical water-insoluble macrolide, is delivered from the star platform to accomplish synergistic antimicrobial activity by the combination of bactericidal-bacteriostatic action of the polymer carrier and drug together in a single system.

Characterization of NK-lysin A, a potent antimicrobial peptide from the zebrafish Danio rerio

Antimicrobial peptides (AMPs) are important players of the innate immune system with a major role in the defense against invading pathogens. AMPs belonging to the family of saposin-like proteins (SAPLIPs) include the porcine NK-lysin and the human granulysin. In the zebrafish Danio rerio, transcript analyses of NK-lysin encoding genes have been reported, but biochemical characterizations at the protein level are missing so far. Here, we present the recombinant expression, purification, and characterization of one of these homologs, namely of NK-lysin A (DaNKlA). To remove the affinity tag from DaNKlA, we made use of a self-splicing intein. Recombinant DaNKlA depolarized liposomes over a broad pH range and showed a preference for negatively charged lipids. DaNKlA inhibited the growth of and killed different Gram-positive and Gram-negative bacteria, including the fish pathogenic bacterium Vibrio anguillarum, by membrane permeabilization but displayed substantially lower activity against yeast cells. Structural modelling and bioinformatic comparison of DaNKlA with characterized SAPLIPs suggest membrane destabilization accompanied by strong electrostatic interactions as the mode of action.

Conjugation of the 9-kDa Isoform of Granulysin with Liposomes Potentiates Its Cytotoxicity

Nine kDa granulysin (GRNLY) is a human cytolytic protein secreted by cytotoxic T lymphocytes (CTL) and NK cells of the immune system whose demonstrated physiological function is the elimination of bacteria and parasites. In previous studies by our group, the anti-tumor capacity of recombinant granulysin was demonstrated, both in vitro and in vivo. In the present work, we developed lipid nanoparticles whose surfaces can bind recombinant granulysin through the formation of a complex of coordination between the histidine tail of the protein and Ni²⁺ provided by a chelating lipid in the liposome composition and termed them LUV-GRNLY, for granulysin-bound large unilamellar vesicles. The objective of this formulation is to increase the granulysin concentration at the site of contact with the target cell and to increase the cytotoxicity of the administered dose. The results obtained in this work indicate that recombinant granulysin binds to the surface of the liposome with high efficiency and that its cytotoxicity is significantly increased when it is in association with liposomes. In addition, it has been demonstrated that the main mechanism of death induced by both granulysin and LUV-GRNLY is apoptosis. Jurkat-shBak cells are resistant to GRNLY and also to LUV-GRNLY, showing that LUV-GRNLY uses the mitochondrial apoptotic pathway to induce cell death. On the other hand, we show that LUV-GRNLY induces the expression of the pro-apoptotic members of the Bcl-2 family Bim and especially PUMA, although it also induced the expression of anti-apoptotic Bcl-x_L. In conclusion, we demonstrate that binding of GRNLY to the surfaces of liposomes clearly augments its cytotoxic potential, with cell death executed mainly by the mitochondrial apoptotic pathway.

Preclinical Studies of Granulysin-Based Anti-MUC1-Tn Immunotoxins as a New Antitumoral Treatment

Two granulysin (GRNLY) based immunotoxins were generated, one containing the scFv of the SM3 mAb (SM3GRNLY) and the other the scFv of the AR20.5 mAb (AR20.5GRNLY). These mAb recognize different amino acid sequences of aberrantly O-glycosylated MUC1, also known as the Tn antigen, expressed in a variety of tumor cell types. We first demonstrated the affinity of these immunotoxins for their antigen using surface plasmon resonance for the purified antigen and flow cytometry for the antigen expressed on the surface of living tumor cells. The induction of cell death of tumor cell lines of different origin positive for Tn antigen expression was stronger in the cases of the immunotoxins than that induced by GRNLY alone. The mechanism of cell death induced by the immunotoxins was studied, showing that the apoptotic component demonstrated previously for GRNLY was also present, but that cell death induced by the immunotoxins included also necroptotic and necrotic components. Finally, we demonstrated the in vivo tumor targeting by the immunotoxins after systemic injection using a xenograft model of the human pancreatic adenocarcinoma CAPAN-2 in athymic mice. While GRNLY alone did not have a therapeutic effect, SM3GRNLY and AR20.5GRNLY reduced tumor volume by 42 and 60%, respectively, compared with untreated tumor-bearing mice, although the results were not statistically significant in the case of AR20.5GRNLY. Histological studies of tumors obtained from treated mice demonstrated reduced cellularity, nuclear morphology compatible with apoptosis induction and active caspase-3 detection by immunohistochemistry. Overall, our results exemplify that these immunotoxins are potential drugs to treat Tn-expressing cancers.

Antibody-Based Immunotoxins for Colorectal Cancer Therapy

Monoclonal antibodies (mAbs) are included among the treatment options for advanced colorectal cancer (CRC). However, while these mAbs effectively target cancer cells, they may have limited clinical activity. A strategy to improve their therapeutic potential is arming them with a toxic payload. Immunotoxins (ITX) combining the cell-killing ability of a toxin with the specificity of a mAb constitute a promising strategy for CRC therapy. However, several important challenges in optimizing ITX remain, including suboptimal pharmacokinetics and especially the immunogenicity of the toxin moiety. Nonetheless, ongoing research is working to solve these limitations and expand CRC patients' therapeutic armory. In this review, we provide a comprehensive overview of targets and toxins employed in the design of ITX for CRC and highlight a wide selection of ITX tested in CRC patients as well as preclinical candidates.

Cellular and Molecular Crosstalk of Graft Endothelial Cells During AMR: Effector Functions and Mechanisms

Graft endothelial cell (EC) injury is central to the pathogenesis of antibody-mediated rejection (AMR). The ability of donor-specific antibodies (DSA) to bind C1q and activate the classical complement pathway is an efficient predictor of graft rejection highlighting complement-dependent cytotoxicity as a key process operating during AMR. In the past 5 y, clinical studies further established the cellular and molecular signatures of AMR revealing the key contribution of other, IgG-dependent and -independent, effector mechanisms mediated by infiltrating NK cells and macrophages. Beyond binding to alloantigens, DSA IgG can activate NK cells and mediate antibody-dependent cell cytotoxicity through interacting with Fcγ receptors (FcγRs) such as FcγRIIIa (CD16a). FcRn, a nonconventional FcγR that allows IgG recycling, is highly expressed on ECs and may contribute to the long-term persistence of DSA in blood. Activation of NK cells and macrophages results in the production of proinflammatory cytokines such as TNF and IFNγ that induce transient and reversible changes in the EC phenotype and functions promoting coagulation, inflammation, vascular permeability, leukocyte trafficking. MHC class I mismatch between transplant donor and recipient can create a situation of "missing self" allowing NK cells to kill graft ECs. Depending on the microenvironment, cellular proximity with ECs may participate in macrophage polarization toward an M1 proinflammatory or an M2 phenotype favoring inflammation or vascular repair. Monocytes/macrophages participate in the loss of endothelial specificity in the process of endothelial-to-mesenchymal transition involved in renal and cardiac fibrosis and AMR and may differentiate into ECs enabling vessel and graft (re)-endothelialization.

Oxidative and Non-Oxidative Antimicrobial Activities of the Granzymes

Cell-mediated cytotoxicity is an essential immune defense mechanism to fight against viral, bacterial or parasitic infections. Upon recognition of an infected target cell, killer lymphocytes form an immunological synapse to release the content of their cytotoxic granules. Cytotoxic granules of humans contain two membrane-disrupting proteins, perforin and granulysin, as well as a homologous family of five death-inducing serine proteases, the granzymes. The granzymes, after delivery into infected host cells by the membrane disrupting proteins, may contribute to the clearance of microbial pathogens through different mechanisms. The granzymes can induce host cell apoptosis, which deprives intracellular pathogens of their protective niche, therefore limiting their replication. However, many obligate intracellular pathogens have evolved mechanisms to inhibit programed cells death. To overcome these limitations, the granzymes can exert non-cytolytic antimicrobial activities by directly degrading microbial substrates or hijacked host proteins crucial for the replication or survival of the pathogens. The granzymes may also attack factors that mediate microbial virulence, therefore directly affecting their pathogenicity. Many mechanisms applied by the granzymes to eliminate infected cells and microbial pathogens rely on the induction of reactive oxygen species. These reactive oxygen species may be directly cytotoxic or enhance death programs triggered by the granzymes. Here, in the light of the latest advances, we review the antimicrobial activities of the granzymes in regards to their cytolytic and non-cytolytic activities to inhibit pathogen replication and invasion. We also discuss how reactive oxygen species contribute to the various antimicrobial mechanisms exerted by the granzymes.

A human apolipoprotein L with detergent-like activity kills intracellular pathogens

Activation of cell-autonomous defense by the immune cytokine interferon-γ (IFN-γ) is critical to the control of life-threatening infections in humans. IFN-γ induces the expression of hundreds of host proteins in all nucleated cells and tissues, yet many of these proteins remain uncharacterized. We screened 19,050 human genes by CRISPR-Cas9 mutagenesis and identified IFN-γ-induced apolipoprotein L3 (APOL3) as a potent bactericidal agent protecting multiple non-immune barrier cell types against infection. Canonical apolipoproteins typically solubilize mammalian lipids for extracellular transport; APOL3 instead targeted cytosol-invasive bacteria to dissolve their anionic membranes into human-bacterial lipoprotein nanodiscs detected by native mass spectrometry and visualized by single-particle cryo-electron microscopy. Thus, humans have harnessed the detergent-like properties of extracellular apolipoproteins to fashion an intracellular lysin, thereby endowing resident nonimmune cells with a mechanism to achieve sterilizing immunity.

A Profound Membrane Reorganization Defines Susceptibility of Plasmodium falciparum Infected Red Blood Cells to Lysis by Granulysin and Perforin

Malaria remains one of the most serious health problems in developing countries. The causative agent of malaria, Plasmodium spp., have a complex life cycle involving multiple developmental stages as well as different morphological, biochemical and metabolic requirements. We recently found that γδ T cells control parasite growth using pore-forming proteins to deliver their cytotoxic proteases, the granzymes, into blood residing parasites. Here, we follow up on the molecular mechanisms of parasite growth inhibition by human pore-forming proteins. We confirm that Plasmodium falciparum infection efficiently depletes the red blood cells of cholesterol, which renders the parasite surrounding membranes susceptible to lysis by prokaryotic membrane disrupting proteins, such as lymphocytic granulysin or the human cathelicidin LL-37. Interestingly, not the cholesterol depletion but rather the simultaneous exposure of phosphatidylserine, a negatively charged phospholipid, triggers resistance of late stage parasitized red blood cells towards the eukaryotic pore forming protein perforin. Overall, by revealing the molecular events we establish here a pathogen-host interaction that involves host cell membrane remodeling that defines the susceptibility towards cytolytic molecules.

Safety and immunogenicity of ChAd63-KH vaccine in post-kala-azar dermal leishmaniasis patients in Sudan

Post-kala-azar dermal leishmaniasis (PKDL) is a chronic, stigmatizing skin condition occurring frequently after apparent clinical cure from visceral leishmaniasis. Given an urgent need for new treatments, we conducted a phase IIa safety and immunogenicity trial of ChAd63-KH vaccine in Sudanese patients with persistent PKDL. LEISH2a (ClinicalTrials.gov: NCT02894008) was an open-label three-phase clinical trial involving sixteen adult and eight adolescent patients with persistent PKDL (median duration, 30 months; range, 6-180 months). Patients received a single intramuscular vaccination of 1 × 10¹⁰ viral particles (v.p.; adults only) or 7.5 × 10¹⁰ v.p. (adults and adolescents), with primary (safety) and secondary (clinical response and immunogenicity) endpoints evaluated over 42-120 days follow-up. AmBisome was provided to patients with significant remaining disease at their last visit. ChAd63-KH vaccine showed minimal adverse reactions in PKDL patients and induced potent innate and cell-mediated immune responses measured by whole-blood transcriptomics and ELISpot. 7/23 patients (30.4%) monitored to study completion showed >90% clinical improvement, and 5/23 (21.7%) showed partial improvement. A logistic regression model applied to blood transcriptomic data identified immune modules predictive of patients with >90% clinical improvement. A randomized controlled trial to determine whether these clinical responses were vaccine-related and whether ChAd63-KH vaccine has clinical utility is underway.

Preparation and Characterization of Liposomal Everolimus by Thin-Film Hydration Technique

In 10% to 40% of the cases of coronary stent implantation, patients face in-stent restenosis due to an inflammatory response, which induces artery thickening. Everolimus, a drug that inhibits growth factor-stimulated cell proliferation of endothelial cells, represents a promising alternative to prevent in-stent restenosis. In this study, everolimus was encapsulated by a film hydration technique in liposomes by using phosphatidylcholine and cholesterol at different ratios. As the ratio of cholesterol increases, it modulates the rigidity of the structure which can affect the encapsulation efficiency of the drug due to steric hindrance. Moreover, various lipid : drug ratios were tested, and it was found that as the lipid : drug ratio increases, the encapsulation efficiency also increases. This behavior is observed because everolimus is a hydrophobic drug; therefore, if the lipidic region increases, more drug can be entrapped into the liposomes. In addition, stability of the encapsulated drug was tested for 4 weeks at 4°C. Our results demonstrate that it is possible to prepare liposomal everolimus by film hydration technique followed by extrusion with high entrapment efficiency as a viable drug delivery system.

Human Term Pregnancy Decidual NK Cells Generate Distinct Cytotoxic Responses

Decidual NK cells (dNK) are the main lymphocyte population in early pregnancy decidual mucosa. Although dNK decrease during pregnancy, they remain present in decidual tissues at term. First trimester dNK facilitate trophoblast invasion, provide protection against infections, and were shown to have many differences in their expression of NKRs, cytokines, and cytolytic capacity compared with peripheral blood NK cells (pNK). However, only limited data are available on the phenotype and function of term pregnancy dNK. In this study, dNK from human term pregnancy decidua basalis and decidua parietalis tissues were compared with pNK and first trimester dNK. Profound differences were found, including: 1) term pregnancy dNK have an increased degranulation response to K562 and PMA/ionomycin but lower capacity to respond to human CMV-infected cells; 2) term pregnancy dNK are not skewed toward recognition of HLA-C, as was previously shown for first trimester dNK; and 3) protein and gene expression profiles identified multiple differences between pNK, first trimester, and term pregnancy dNK, suggesting term pregnancy dNK are a distinct type of NK cells. Understanding the role of dNK throughout pregnancy is of high clinical relevance for studies aiming to prevent placental inflammatory disorders as well as maternal-to-fetal transmission of pathogens.

Knocking 'em Dead: Pore-Forming Proteins in Immune Defense

Immune cells use a variety of membrane-disrupting proteins [complement, perforin, perforin-2, granulysin, gasdermins, mixed lineage kinase domain-like pseudokinase (MLKL)] to induce different kinds of death of microbes and host cells, some of which cause inflammation. After activation by proteolytic cleavage or phosphorylation, these proteins oligomerize, bind to membrane lipids, and disrupt membrane integrity. These membrane disruptors play a critical role in both innate and adaptive immunity. Here we review our current knowledge of the functions, specificity, activation, and regulation of membrane-disrupting immune proteins and what is known about the mechanisms behind membrane damage, the structure of the pores they form, how the cells expressing these lethal proteins are protected, and how cells targeted for destruction can sometimes escape death by repairing membrane damage.

Kinetoplastid Membrane Protein-11 Induces Pores in Anionic Phospholipid Membranes: Effect of Cholesterol

Kinetoplastid membrane protein-11 (KMP-11), expressed in all stages of leishmanial life cycle, is considered a potential candidate for leishmaniasis vaccine. KMP-11 is found on the membrane surface of the parasite. Although the biological function of KMP-11 is unknown, we hypothesize from its sequence analysis that it may interact with the macrophage membrane and may influence the entry process of the parasite into the host cell. To validate this hypothesis, we have investigated the interaction of KMP-11 with unilamellar anionic phospholipid vesicles and explored its pore-forming activity. The decrease in negative ζ-potential of the vesicles and reduction in the fluorescence intensity of membrane-bound dye DiI C-18 suggest a strong association of KMP-11 with the membrane. The fluorescence leakage experiment as well as phase contrast microscopy shows direct evidence of KMP-11-induced pore formation in an anionic membrane. Incorporation of cholesterol into the membrane has been found to inhibit pore formation induced by KMP-11, suggesting an important role of cholesterol in leishmaniasis. Interestingly, vesicles containing only neutral phospholipid do not exhibit any tendency toward pore formation.

Granzyme B Attenuates Bacterial Virulence by Targeting Secreted Factors

Pathogenic bacteria secrete virulence factors that interact with the human host to establish infections. The human immune system evolved multiple mechanisms to fight bacterial invaders, including immune proteases that were demonstrated to contribute crucially to antibacterial defense. Here we show that granzyme B degrades multiple secreted virulence mediators from Listeria monocytogenes, Salmonella typhimurium, and Mycobacteria tuberculosis. Pathogenic bacteria, when infected in the presence of granzyme B or granzyme-secreting killer cells, fail to grow in human macrophages and epithelial cells owing to their crippled virulence. A granzyme B-uncleavable mutant form of the major Listeria virulence factor, listeriolysin O, rescued the virulence defect in response to granzyme treatment. Hence, we link the degradation of a single factor with the observed decrease in virulent bacteria growth. Overall, we reveal here an innate immune barrier function of granzyme B by disrupting bacterial virulence to facilitate bacteria clearance by bystander immune and non-immune cells.

γδ T Cells Kill Plasmodium falciparum in a Granzyme- and Granulysin-Dependent Mechanism during the Late Blood Stage

Plasmodium spp., the causative agent of malaria, have a complex life cycle. The exponential growth of the parasites during the blood stage is responsible for almost all malaria-associated morbidity and mortality. Therefore, tight immune control of the intraerythrocytic replication of the parasite is essential to prevent clinical malaria. Despite evidence that the particular lymphocyte subset of γδ T cells contributes to protective immunity during the blood stage in naive hosts, their precise inhibitory mechanisms remain unclear. Using human PBMCs, we confirmed in this study that γδ T cells specifically and massively expanded upon activation with Plasmodium falciparum culture supernatant. We also demonstrate that these activated cells gain cytolytic potential by upregulating cytotoxic effector proteins and IFN-γ. The killer cells bound to infected RBCs and killed intracellular P. falciparum via the transfer of the granzymes, which was mediated by granulysin in a stage-specific manner. Several vital plasmodial proteins were efficiently destroyed by granzyme B, suggesting proteolytic degradation of these proteins as essential in the lymphocyte-mediated death pathway. Overall, these data establish a granzyme- and granulysin-mediated innate immune mechanism exerted by γδ T cells to kill late-stage blood-residing P. falciparum.

Granulysin: killer lymphocyte safeguard against microbes

Primary T cell immunodeficiency and HIV-infected patients are plagued by non-viral infections caused by bacteria, fungi, and parasites, suggesting an important and underappreciated role for T lymphocytes in controlling microbes. Here, we review recent studies showing that killer lymphocytes use the antimicrobial cytotoxic granule pore-forming peptide granulysin, induced by microbial exposure, to permeabilize cholesterol-poor microbial membranes and deliver death-inducing granzymes into these pathogens. Granulysin and granzymes cause microptosis, programmed cell death in microbes, by inducing reactive oxygen species and destroying microbial antioxidant defenses and disrupting biosynthetic and central metabolism pathways required for their survival, including protein synthesis, glycolysis, and the Krebs cycle.

Activated cytotoxic T cells within zoonotic cutaneous leishmaniasis lesions

Introduction

Zoonotic cutaneous leishmaniasis (ZCL), due to infection by Leishmania (L). major, is characterized by polymorphic clinical manifestations which could be attributed to the host's immune response. In this study we investigated the involvement of cytotoxic cells on the outcome of the disease.

Methods

Expression of granzyme B (GrB), granulysine (Grly), and interferon (IFN)‐γ was evaluated within ZCL lesion specimens using the technique of real‐time quantitative polymerase chain reaction (RT‐qPCR). Immunohistochemical staining was performed using anti‐CD3, CD4, CD8, CD56, GrB, and IFN‐γ antibodies to identify the phenotype of GrB and IFN‐γ‐producing cells.

Results

GrB and Grly mRNA was detected within 75% and 80% of ZCL lesions, respectively. Statistical analysis demonstrated a significant correlation between levels of GrB and Grly. Interestingly, expression of these molecules correlates negatively with the lesion's age. The highest levels were measured in early lesions (E‐ZCL) (lesion age ≤1 month) comparing to late lesions (L‐ZCL) (lesion age >1 month). Otherwise, IFN‐γ mRNA was detected only within 56% and a positive correlation was found between levels of this cytokine and those of GrB. Immunohistochemical analysis showed that GrB is produced essentially by CD8⁺T cells whereas IFN‐γ is produced by both CD4⁺ and CD8⁺T cells.

Conclusion

Together our results demonstrate the presence of cytotoxic cells producing GrB and Grly within leishmaniasis cutaneous lesions.

Microbial killing by NK cells

It is now evident that NK cells kill bacteria, fungi, and parasites in addition to tumor and virus-infected cells. In addition to a number of recent publications that have identified the receptors and ligands, and mechanisms of cytotoxicity, new insights are reflected in the reports from researchers all over the world at the 17th Meeting of the Society for Natural Immunity held in San Antonio, TX, USA from May 28 through June 1, 2018. We will provide an overview of the field and discuss how the presentations at the meeting might shape our knowledge and future directions in the field.

Cytotoxic CD8+ T cells recognize and kill Plasmodium vivax-infected reticulocytes

Plasmodium vivax causes approximately 100 million clinical malaria cases yearly^1,2. The basis of protective immunity is poorly understood and thought to be mediated by antibodies^3,4. Cytotoxic CD8⁺ T cells (CTLs) protect against other intracellular parasites by detecting parasite peptides presented by Human Leukocyte Antigen Class I (HLA-I) on host cells. CTLs kill parasite-infected mammalian cells and intracellular parasites by releasing their cytotoxic granules^5,6. Perforin (PFN) delivers the antimicrobial peptide granulysin (GNLY) and death-inducing granzymes (Gzm) into the host cell, and GNLY then delivers Gzms into the parasite. CTLs were thought to have no role against Plasmodium spp. blood stages because red blood cells (RBCs) generally do not express HLA-I⁷. However, P. vivax infects reticulocytes (Retics) that retain the protein translation machinery. Here we show that P. vivax-infected Retics (iRetic) express HLA-I. Infected patient circulating CD8⁺ T cells highly express cytotoxic proteins and recognize and form immunological synapses with iRetics in an HLA-dependent manner, releasing their cytotoxic granules to kill both host cell and intracellular parasite, preventing reinvasion. iRetic and parasite killing is PFN-independent, but depends on GNLY, which generally efficiently forms pores only in microbial membranes⁸. We find that P. vivax depletes cholesterol from the iRetic cell membrane, rendering it GNLY-susceptible. This unexpected T cell defense might be mobilized to improve P. vivax vaccine efficacy.

Granzyme B Disrupts Central Metabolism and Protein Synthesis in Bacteria to Promote an Immune Cell Death Program

Human cytotoxic lymphocytes kill intracellular microbes. The cytotoxic granule granzyme proteases released by cytotoxic lymphocytes trigger oxidative bacterial death by disrupting electron transport, generating superoxide anion and inactivating bacterial oxidative defenses. However, they also cause non-oxidative cell death because anaerobic bacteria are also killed. Here, we use differential proteomics to identify granzyme B substrates in three unrelated bacteria: Escherichia coli, Listeria monocytogenes, and Mycobacteria tuberculosis. Granzyme B cleaves a highly conserved set of proteins in all three bacteria, which function in vital biosynthetic and metabolic pathways that are critical for bacterial survival under diverse environmental conditions. Key proteins required for protein synthesis, folding, and degradation are also substrates, including multiple aminoacyl tRNA synthetases, ribosomal proteins, protein chaperones, and the Clp system. Because killer cells use a multipronged strategy to target vital pathways, bacteria may not easily become resistant to killer cell attack.

Cytotoxic potential of decidual NK cells and CD8+ T cells awakened by infections

To establish a healthy pregnancy the maternal immune system must tolerate fetal allo-antigens, yet remain competent to respond to infections. The ability of decidual NK cells (dNK) to promote migration of fetal extravillous trophoblasts (EVT) and placental growth as well as the capacity of EVT to promote immune tolerance are topics of high interest and extensive research. However, the problem of how dNK and decidual CD8+ T cells (CD8+ dT) provide immunity to infections of the placenta and the mechanisms that regulate their cytolytic function has thus far largely been ignored. Fetal EVT are the most invasive cells of the placenta and directly interact with maternal decidual immune cells at this maternal-fetal interface. Besides the expression of non-polymorphic HLA-E and HLA-G molecules that are associated with immune tolerance, EVT also express highly polymorphic HLA-C molecules that can serve as targets for maternal dNK and CD8+ dT responses. HLA-C expression by EVT has a dual role as the main molecule to which immune tolerance needs to be established and as the only molecule that can present pathogen-derived peptides and provide protective immunity when EVT are infected. The focus of this review is to address the regulation of cytotoxicity of dNK and CD8+ dT, which is essential for maternal-fetal immune tolerance as well as recent evidence that both cell types can provide immunity to infections at the maternal-fetal interface. A particular emphasis is given to the role of HLA-C expressed by EVT and its capacity to elicit dNK and CD8+ dT responses.

Killing Bacteria with Cytotoxic Effector Proteins of Human Killer Immune Cells: Granzymes, Granulysin, and Perforin

Bacterial pathogens represent a constant threat to human health that was exacerbated in recent years by a dramatic increase of strains resistant to last resort antibiotics. The immune system of higher vertebrates generally evolved several efficient innate and adaptive mechanisms to fight ubiquitous bacterial pathogens. Among those mechanisms, immune proteases were recognized to contribute essentially to antibacterial immune defense. The effector serine proteases of the adaptive immune system, the granzymes, exert potent antimicrobial activity when they are delivered into the bacterial cytosol by prokaryotic membrane disrupting proteins, such as granulysin.In this chapter, we are detailing experimental protocols to study the synergistic cytotoxic effects of human granzymes and granulysin on extracellular as well as on intracellular bacterial pathogens in vitro. In addition, we provide a simple and fast-forward method to biochemically purify native cytotoxic effector molecules necessary to perform this kind of investigations.

Killer lymphocytes use granulysin, perforin and granzymes to kill intracellular parasites

Protozoan infections are a serious global health problem. Natural killer (NK) cells and cytolytic T lymphocytes (CTLs) eliminate pathogen-infected cells by releasing cytolytic granule contents--granzyme (Gzm) proteases and the pore-forming perforin (PFN)--into the infected cell. However, these cytotoxic molecules do not kill intracellular parasites. CD8(+) CTLs protect against parasite infections in mice primarily by secreting interferon (IFN)-γ. However, human, but not rodent, cytotoxic granules contain the antimicrobial peptide granulysin (GNLY), which selectively destroys cholesterol-poor microbial membranes, and GNLY, PFN and Gzms rapidly kill intracellular bacteria. Here we show that GNLY delivers Gzms into three protozoan parasites (Trypanosoma cruzi, Toxoplasma gondii and Leishmania major), in which the Gzms generate superoxide and inactivate oxidative defense enzymes to kill the parasite. PFN delivers GNLY and Gzms into infected cells, and GNLY then delivers Gzms to the intracellular parasites. Killer cell-mediated parasite death, which we term 'microbe-programmed cell death' or 'microptosis', is caspase independent but resembles mammalian apoptosis, causing mitochondrial swelling, transmembrane potential dissipation, membrane blebbing, phosphatidylserine exposure, DNA damage and chromatin condensation. GNLY-transgenic mice are protected against infection by T. cruzi and T. gondii, and survive infections that are lethal to wild-type mice. Thus, GNLY-, PFN- and Gzm-mediated elimination of intracellular protozoan parasites is an unappreciated immune defense mechanism.

Formation and Characterization of Supported Lipid Bilayers Composed of Hydrogenated and Deuterated Escherichia coli Lipids

Supported lipid bilayers are widely used for sensing and deciphering biomolecular interactions with model cell membranes. In this paper, we present a method to form supported lipid bilayers from total lipid extracts of Escherichia coli by vesicle fusion. We show the validity of this method for different types of extracts including those from deuterated biomass using a combination of complementary surface sensitive techniques; quartz crystal microbalance, neutron reflection and atomic force microscopy. We find that the head group composition of the deuterated and the hydrogenated lipid extracts is similar (approximately 75% phosphatidylethanolamine, 13% phosphatidylglycerol and 12% cardiolipin) and that both samples can be used to reconstitute high-coverage supported lipid bilayers with a total thickness of 41 ± 3 Å, common for fluid membranes. The formation of supported lipid bilayers composed of natural extracts of Escherichia coli allow for following biomolecular interactions, thus advancing the field towards bacterial-specific membrane biomimics.

Possible role of granulysin in pathogenesis of osteoarthritis

Increased presence of immune mediator and cytotoxic/apoptotic molecule granulysin was noticed in different tissues during pathological processes with the domination of Th1 over Th2 mediated immunity. Beside granulysin expression in T and NKT cells, activated NK cells are thought to be the major source of chemotactic 15 kDa and cytotoxic 9 kDa granulysin in vivo. As NK cells are the principal joint's tissue-infiltrating lymphocyte subset, we hypothesized that granulysin mediated human cell death (apoptosis) could be responsible for the relatively silent damage of the joint's tissue without clinically notable signs of systemic inflammation in the patients with osteoarthritis (OA). The analyzes of the presence and frequency of granulysin expressing lymphocytes at protein and gene levels in peripheral blood and synovial samples and/or the samples of joint's tissue after the joint replacement therapy in patients with OA could give the initial insight to evaluate our hypothesis. It would be of the particular interest to differentiate the expression of 9 kDa and 15 kDa granulysin forms in the effector cells, since only the shorter form exhibits cytotoxic properties. The measurement of granulysin mediated early apoptosis in human NK sensitive K562 cells could be suitable in vitro model for evaluating granulysin activity. Furthermore, disturbed balance of pro-inflammatory and anti-inflammatory cytokines in OA patients, could influence the level of the granulysin expression. Having in mind that the granulysin and its regulation is still unknown in the pathogenesis of OA, it could be worth to explore this important pro-inflammatory, cytotoxic/apoptotic mediator.

Expression of genes associated with cholesterol and lipid metabolism identified as a novel pathway in the early pathogenesis of Mycobacterium avium subspecies paratuberculosis-infection in cattle

Johne's disease (JD) is a chronic disease affecting ruminants and other species caused by the pathogenic mycobacterium, Mycobacterium avium subsp. paratuberculosis (MAP). MAP has developed a multitude of mechanisms to persist within the host, and these in turn are counteracted by the host through various immune pathways. Identifying and characterising the different strategies employed by MAP to alter the host immune system in its favour, and thereby persist intracellularly, could hold the key to developing strategies to fight this disease. In this study we analysed a subset of bovine microarray data derived from early time points after experimental infection with MAP. A specifically developed integrated approach was used to identify and validate host genes involved in cholesterol homeostasis (24DHCR, LDLR, SCD-1), calcium homeostasis and anti-bacterial defence mechanisms, (CD38, GIMAP6) which were downregulated in response to MAP exposure. A trend for upregulation of granulysin gene expression in MAP-exposed cattle in comparison to unexposed cattle was also observed. From these analyses, a model of potential pathogen-host interactions involving these novel pathways was developed which indicates an important role for host lipids in mycobacterial survival and persistence.

Granulysin expression and the interplay of granulysin and perforin at the maternal-fetal interface

Granulysin (GNLY) is a cytolytic/apoptotic molecule highly expressed in immune cells, particularly NK cells, at the maternal-fetal interface. The primary function of GNLY is to carry out lysis or apoptosis induction in target cells, tumor cells or cells infected by intracellular pathogens. To exert some of its functions GNLY needs to collaborate with perforin. The purpose of this study was to determine: (a) the expression of GNLY at the gene and protein levels at the maternal-fetal interface, (b) the relationship(s) between GNLY and perforin, and (c) GNLY secretion by NK cells stimulated by the NK-sensitive K562 cell line and its HLA-C and HLA-G transfectants. GNLY and perforin genes were found to be highly activated at the interface. GNLY mRNA was present at significantly higher levels compared with other cytolytic/apoptotic molecules. Confocal microscopy analysis showed that most first trimester pregnancy decidual lymphocytes simultaneously contained both GNLY and perforin protein in their cytoplasm, with a punctuate pattern consistent with granule localization. In contrast to peripheral blood, in unstimulated decidual lymphocytes GNLY and perforin rarely co-localized (10% of GNLY-positive cells and 20% of perforin-positive cells were positive for both proteins). Contact between decidual lymphocytes and K562 cells caused GNLY and perforin to be expressed in the same granules (approximately 50% co-localization), i.e., to attain the pattern seen in peripheral blood lymphocytes. The abundant GNLY secretion by decidual NK cells compared with peripheral blood NK cells after 2h of contact with the NK-sensitive K562 cells and K562 transfectants was striking.

An atomic-force basis for the bacteriolytic effects of granulysin

While granulysin has been suggested to play an important role in adaptive immune responses against bacterial infections by killing pathogens, and molecular force for protein-protein interaction or protein-bacteria interaction may designate the specific functions of a protein, the molecular-force basis underlying the bacteriolytic effects of granulysin at single-molecule level remains unknown. Here, we produced and purified bactericidal domain of macaque granulysin (GNL). Our bacterial lysis assays suggested that GNL could efficiently kill bacteria such as Listeria monocytogenes. Furthermore, we found that the interaction force between GNL and L. monocytogenes measured by an atomic force microscopy (AFM) was about 22.5 pN. Importantly, our AFM-based single molecular analysis suggested that granulysin might lyse the bacteria not only through electrostatic interactions but also by hydrogen bonding and van der Waals interaction. Thus, this work provides a previous unknown mechanism for bacteriolytic effects of granulysin.

Chlorhexidine: beta-cyclodextrin inhibits yeast growth by extraction of ergosterol

Chlorhexidine (Cx) augmented with beta-cyclodextrin (β-cd) inclusion compounds, termed Cx:β-cd complexes, have been developed for use as antiseptic agents. The aim of this study was to examine the interactions of Cx:β-cd complexes, prepared at different molecular ratios, with sterol and yeast membranes. The Minimal Inhibitory Concentration (MIC) against the yeast Candida albicans (C.a.) was determined for each complex; the MICs were found to range from 0.5 to 2 μg/mL. To confirm the MIC data, quantitative analysis of viable cells was performed using trypan blue staining. Mechanistic characterization of the interactions that the Cx:β-cd complexes have with the yeast membrane and assessment of membrane morphology following exposure to Cx:β-cd complexes were performed using Sterol Quantification Method analysis (SQM) and scanning electron microscopy (SEM). SQM revealed that sterol extraction increased with increasing β-cd concentrations (1.71 ×10³; 1.4 ×10³; 3.45 ×10³, and 3.74 ×10³ CFU for 1:1, 1:2, 1:3, and 1:4, respectively), likely as a consequence of membrane ergosterol solubilization. SEM images demonstrated that cell membrane damage is a visible and significant mechanism that contributes to the antimicrobial effects of Cx:β-cd complexes. Cell disorganization increased significantly as the proportion of β-cyclodextrin present in the complex increased. Morphology of cells exposed to complexes with 1:3 and 1:4 molar ratios of Cx:β-cd were observed to have large aggregates mixed with yeast remains, representing more membrane disruption than that observed in cells treated with Cx alone. In conclusion, nanoaggregates of Cx:β-cd complexes block yeast growth via ergosterol extraction, permeabilizing the membrane by creating cluster-like structures within the cell membrane, possibly due to high amounts of hydrogen bonding.

Effect of cholesterol on the membrane interaction of Modelin-5 isoforms

Modelin-5 isoforms were used to gain an insight into the effects of amidation on antimicrobial selectivity. When tested against Escherichia coli, amidation increased toxicity 10-fold (MIC = 31.25 μM) while showing limited increased hemolytic activity (2% lysis). Our results show that both the amidated and non-amidated peptides had a disordered structure in aqueous solution (<18% helical) and folded to form helices at the membrane interface (for example, >43% in the presence of DMPC). The stabilization of the helical structure by amidation has previously been shown to play a key role in increasing antibacterial efficacy. The presence of cholesterol in the membrane increases the packing density (C(s)(-1) values 25-33 mN m(-1)) and so prevents the peptide from forming stable association with the membrane, which is evidenced by the higher binding coefficient (K(d)) in the presence of cholesterol: 57.70 μM for Modelin-5-COOH and 35.64 μM for Modelin-5-CONH(2) compared to the presence of E. coli lipid extract (10 μM), which would prevent local concentration of the peptide at the bilayer interface as seen by reduction in monolayer interaction. This in turn would be predicted to inhibit activity.

Cell death mechanisms at the maternal-fetal interface: insights into the role of granulysin

During mammal pregnancy, a sensitive balance between hormones, cytokines, humoral factors, and local cellular interactions must be established. Cytotoxic cells infiltrating the decidua are heavily equipped with cytolytic molecules, in particular perforin and granulysin. Granulysin is especially abundant in NK cells which are able to spontaneously secrete high quantities of granulysin. Besides being a potent bactericidal and tumoricidal molecule, granulysin is also found to be a chemoattractant and a proinflammatory molecule. The precise role(s) of granulysin at the maternal-fetal interface has not been elucidated yet. It is possible that it behaves as a double-edged sword simultaneously acting as an immunomodulatory and a host defense molecule protecting both the mother and the fetus from a wide spectrum of pathogens, and on the other hand, in case of an NK cell activation, acting as an effector molecule causing the apoptosis of semiallograft trophoblast cells and consequently leading to various pregnancy disorders or pregnancy loss.

First trimester pregnancy decidual natural killer cells contain and spontaneously release high quantities of granulysin

PROBLEM

Granulysin (GNLY) is a novel cytolytic protein lytic against a variety of tumor cells and microbes. The role of GNLY during pregnancy has not been extensively explored. The aim of this study is to examine GNLY expression and distribution in the first trimester pregnancy peripheral blood (PB) and decidua, the ability of decidual and PB natural killer (NK) cells to secrete GNLY spontaneously, and the role of antigen-presenting cells (APC) in the regulation of GNLY expression in decidual NK cells.

METHOD OF STUDY

GNLY expression was analyzed using cell permeabilization method, flow cytometry, and immunohistochemistry. GNLY secretion by purified NK cells was detected by ELISA method.

RESULTS

GNLY is abundantly expressed at the maternal-fetal interface in the first trimester pregnancy. Decidual T lymphocytes express significantly higher levels of GNLY (58%) then PB T lymphocytes (11%). Over 85% of decidual CD56(+) cells express GNLY and when cultured spontaneously release high quantities of GNLY. Decidual APC participate in the control of GNLY expression in CD56(+) cells.

CONCLUSION

Abundant expression of GNLY in the decidual immunocompetent cells and the capacity of decidual CD56(+) cells to spontaneously secrete high quantities of GNLY point to important protective and immunomodulatory role that this molecule could play at the maternal-fetal interface.

Morphological changes induced by the action of antimicrobial peptides on supported lipid bilayers

We utilized epifluorescence microscopy to investigate the morphological changes in labeled lipid bilayers supported on quartz surfaces (SLBs) induced by the interaction of cationic antimicrobial peptides with the lipid membranes. The SLBs were prepared from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and mixtures thereof as well as from Escherichia coli lipid extract. We succeeded in the preparation of POPG and POPG-rich SLBs without the necessity to use fusogenic agents such as calcium by using the Langmuir-Blodgett/Langmuir-Schaefer transfer method. The adsorption of the peptides to the SLBs was initially driven by electrostatic interactions with the PG headgroups and led to the formation of lipid protrusions bulging out from the lipid layer facing the bulk, originating particularly from domain boundaries and membrane defects. The shape, size, and frequency of the lipid protrusions are mainly controlled by the peptide macroscopic properties and the membrane composition. A restructuring of the lipid protrusions into other structures can also occur over time.

Granulysin activates antigen-presenting cells through TLR4 and acts as an immune alarmin

Granulysin (GNLY), an antimicrobial protein present in the granules of human cytotoxic T lymphocytes and natural killer (NK) cells, is produced as an intact 15-kDa form that is cleaved to yield a 9-kDa form. Alarmins are endogenous mediators that can induce recruitment and activation of antigen-presenting cells (APCs) and consequently promote the generation of immune response. We hypothesized that GNLY might function as an alarmin. Here, we report that both 9- and 15-kDa forms of recombinant GNLY-induced in vitro chemotaxis and activation of both human and mouse dendritic cells (DCs), recruited inflammatory leucocytes, including APCs in mice, and promoted antigen-specific immune responses upon coadministration with an antigen. GNLY-induced APC recruitment and activation required the presence of Toll-like receptor 4. The observed activity of recombinant GNLY was not due to endotoxin contamination. The capability of the supernatant of GNLY-expressing HuT78 cells to activate DC was blocked by anti-GNLY antibodies. Finally we present evidence that supernatants of degranulated human NK92 or primary NK cells also activated DCs in a GNLY- and Toll-like receptor 4-dependent manner, indicating the physiologic relevance of our findings. Thus, GNLY is the first identified lymphocyte-derived alarmin capable of promoting APC recruitment, activation, and antigen-specific immune response.

Involvement of CD252 (CD134L) and IL-2 in the expression of cytotoxic proteins in bacterial- or viral-activated human T cells

Regulation of cytotoxic effector molecule expression in human CTLs after viral or bacterial activation is poorly understood. By using human autologous dendritic cells (DCs) to prime T lymphocytes, we found perforin only highly up-regulated in virus- (HSV-1, vaccinia virus) but not in intracellular bacteria- (Listeria innocua, Listeria monocytogenes, Mycobacterium tuberculosis, Chlamydophila pneumoniae) activated CTLs. In contrast, larger quantities of IFN-gamma and TNF-alpha were produced in Listeria-stimulated cultures. Granzyme B and granulysin were similarly up-regulated by all tested viruses and intracellular bacteria. DCs infected with HSV-1 showed enhanced surface expression of the costimulatory molecule CD252 (CD134L) compared with Listeria-infected DC and induced enhanced secretion of IL-2. Adding blocking CD134 or neutralizing IL-2 Abs during T cell activation reduced the HSV-dependent up-regulation of perforin. These data indicate a distinct CTL effector function in response to intracellular pathogens triggered via differing endogenous IL-2 production upon costimulation through CD252.

Granulysin induces cathepsin B release from lysosomes of target tumor cells to attack mitochondria through processing of bid leading to Necroptosis

Granulysin is a killer effector molecule localized in cytolytic granules of human NK and CTL cells. Granulysin exhibits broad antimicrobial activity and potent cytotoxic action against tumor cells. However, the molecular mechanism of granulysin-induced tumor lysis is poorly understood. In this study, we found that granulysin causes a novel cell death termed necroptosis. Granulysin can target lysosomes of target tumor cells and induce partial release of lysosomal contents into the cytosol. Relocalized lysosomal cathepsin B can process Bid to active tBid to cause cytochrome c and apoptosis-activating factor release from mitochondria. Cathepsin B silencing and Bid or Bax/Bak deficiency resists granulysin-induced cytochrome c and apoptosis-activating factor release and is less susceptible to cytolysis against target tumor cells.

Unique membrane-interacting properties of the immunostimulatory cationic peptide KLKL(5)KLK (KLK)

We have monitored the effects of KLKL(5)KLK (KLK), a derivative of a natural cationic antimicrobial peptide (CAP) on isolated membrane vesicles, and investigated the partition of the peptide within these structures. KLK readily interacted with fluorescent dyes entrapped in the vesicles without apparent pore formation. Fractionation of vesicles revealed KLK predominantly in the membrane. Peptide-treated vesicles appeared with generally disorganized bilayers. While KLK showed no effect on osmotic resistance of human erythrocytes, dramatic decrease in core and surface membrane fluidity was observed in peptide-treated erythrocyte ghosts as measured by fluorescence anisotropy. Finally, CD spectroscopy revealed lipid-induced random coil to beta-sheet and beta-sheet to alpha-helix conformational transitions of KLK. Together with the oligonucleotide oligo-d(IC)(13) [ODN1a], KLK functions as a novel adjuvant, termed IC31. Among other immunological effects, KLK appears to facilitate the uptake and delivery of ODN1a into cellular compartments, but the nature of KLK's interaction with the cell surface and other membrane-bordered compartments remains unknown. Our results suggest a profound membrane interacting property of KLK that might contribute to the immunostimulatory activities of IC31.