A novel serine esterase expressed by cytotoxic T lymphocytes

Factors contributing to the potency of CD8+ T cells

CD8+ cytotoxic T lymphocytes (CTLs) play a crucial role in targeting virus-infected and cancer cells. Although other cytotoxic lymphocytes such as CD4+ T and natural killer (NK) cells, as well as chimeric antigen receptor (CAR)-T cells, can also identify and destroy aberrant cells, they seem to be significantly less potent based on available experimental data. Here, I contemplate the molecular mechanisms controlling the sensitivity and kinetics of granule-mediated CD8+ T cell cytolytic responses. I posit that the clustering of MHC-I molecules and T cell receptors (TCRs) on the cell surface, as well as the contribution of the CD8 co-receptor, are major factors driving exceptionally potent cytolytic responses. I also contend that CD8+ T cells with known specificity and engineered TCR-T cells might be among the most efficient cytolytic effectors for treating patients suffering from viral infections or cancer.

Determination and Quantitation of Cytotoxic T Cell-Mediated Cell Death

Cytotoxic T cell-induced cell death is well documented. Cytotoxic T cell releases various cytolytic proteins. The cytolytic proteins induce target cell death. T cell-induced cell death can be measured by the lytic assay. One of the well-known lytic assays uses radioactive tracer, Chromium-51 (⁵¹Cr), and detects the amount of ⁵¹Cr released from target cells. This assay can detect cell death and the efficiency of the T cell-induced cell death by coculture effector cells (T cells) and target cells. This assay can determine the kinetics of the cell lysis. The issue of this approach is the use of radioactive material. This chapter describes measuring T cell-induced cell death by determining the epigenetic remodeling and the release of cytolytic proteins. Determine the efficiency of T cell-induced cell death by using a flow cytometry-based detection method.

IL-1α Processing, Signaling and Its Role in Cancer Progression

Interleukin-1α (IL-1α) is a major alarmin cytokine which triggers and boosts the inflammatory responses. Since its discovery in the 1940s, the structure and bioactivity of IL-1α has been extensively studied and emerged as a vital regulator in inflammation and hematopoiesis. IL-1α is translated as a pro-form with minor bioactivity. The pro-IL-1α can be cleaved by several proteases to generate the N terminal and C terminal form of IL-1α. The C terminal form of IL-1α (mature form) has several folds higher bioactivity compared with its pro-form. IL-1α is a unique cytokine which could localize in the cytosol, membrane, nucleus, as well as being secreted out of the cell. However, the processing mechanism and physiological significance of these differentially localized IL-1α are still largely unknown. Accumulating evidence suggests IL-1α is involved in cancer pathogenesis. The role of IL-1α in cancer development is controversial as it exerts both pro- and anti-tumor roles in different cancer types. Here, we review the recent development in the processing and signaling of IL-1α and summarize the functions of IL-1α in cancer development.

Immunosenescence Modulation by Vaccination

A decline in immune function is a hallmark of aging that leads to complicated illness from a variety of infectious diseases, cancer and other immune-mediated disorders, and may limit the ability to appropriately respond to vaccination. How vaccines might alter the senescent immune response and what are the immune correlates of protection will be addressed from the perspective of (1) stimulating a previously primed response as in the case of vaccines for seasonal influenza and herpes zoster, (2) priming the response to novel antigens such as pandemic influenza or West Nile virus, (3) vaccination against bacterial pathogens such as pneumococcus and pertussis, (4) vaccines against bacterial toxins such as tetanus and Clostridium difficile, and (5) vaccine approaches to mitigate effects of cytomegalovirus on immune senescence. New or improved vaccines developed over recent years demonstrate the considerable opportunity to improve current vaccines and develop new vaccines as a preventive approach to a variety of diseases in older adults. Strategies for selecting appropriate immunologic targets for new vaccine development and evaluating how vaccines may alter the senescent immune response in terms of potential benefits and risks in the preclinical and clinical trial phases of vaccine development will be discussed.

A Role for the Chaperone Complex BAG3-HSPB8 in Actin Dynamics, Spindle Orientation and Proper Chromosome Segregation during Mitosis

The co-chaperone BAG3, in complex with the heat shock protein HSPB8, plays a role in protein quality control during mechanical strain. It is part of a multichaperone complex that senses damaged cytoskeletal proteins and orchestrates their seclusion and/or degradation by selective autophagy. Here we describe a novel role for the BAG3-HSPB8 complex in mitosis, a process involving profound changes in cell tension homeostasis. BAG3 is hyperphosphorylated at mitotic entry and localizes to centrosomal regions. BAG3 regulates, in an HSPB8-dependent manner, the timely congression of chromosomes to the metaphase plate by influencing the three-dimensional positioning of the mitotic spindle. Depletion of BAG3 caused defects in cell rounding at metaphase and dramatic blebbing of the cortex associated with abnormal spindle rotations. Similar defects were observed upon silencing of the autophagic receptor p62/SQSTM1 that contributes to BAG3-mediated selective autophagy pathway. Mitotic cells depleted of BAG3, HSPB8 or p62/SQSTM1 exhibited disorganized actin-rich retraction fibres, which are proposed to guide spindle orientation. Proper spindle positioning was rescued in BAG3-depleted cells upon addition of the lectin concanavalin A, which restores cortex rigidity. Together, our findings suggest the existence of a so-far unrecognized quality control mechanism involving BAG3, HSPB8 and p62/SQSTM1 for accurate remodelling of actin-based mitotic structures that guide spindle orientation.

Small heat shock proteins (sHSP/HSPB) form a diverse family of ATP-independent chaperones. Some of them protect the proteome against aggregation during stress and others regulate normal biological processes through ill-defined mechanisms. Interactions between HSPB proteins and elements of the cytoskeleton are increasingly linked to their implication in human degenerative diseases and cancer. For instance, a multichaperone complex containing HSPB8 and its co-chaperone BAG3 would maintain muscle cell integrity by promoting the autophagic clearance of damaged components within F-actin structures. Selective autophagy is a targeted protein degradation mechanism for elimination of damaged organelles and proteins. It may also regulate removal of signaling proteins from their functionally relevant sites during intense remodeling of the cytoskeleton, as it occurs during mitosis. Here, we report a novel role for HSPB8 and BAG3 during mitosis in mammalian cells that involves the autophagic receptor p62/SQSTM1. We show that a reduction of any protein within the HSPB8-BAG3-p62/SQSTM signaling axis similarly impairs mitotic progression and chromosome segregation by affecting orientation of the mitotic spindle and assembly of mitotic-specific actin structures. Our findings establish a unique role for HSPB8 in a novel function of BAG3 in mitotic cell division and genome stability, through effect on remodeling of the actin cytoskeleton.

Cloning and characterization of a novel acidic cutinase from Sirococcus conigenus

A cutinase gene (ScCut1) was amplified by PCR from the genomic DNA of the ascomycetous plant pathogen Sirococcous conigenus VTT D-04989 using degenerate primers designed on the basis of conserved segments of known cutinases and cutinase-like enzymes. No introns or N- or O-glycosylation sites could be detected by analysis of the ScCut1 gene sequence. The alignment of ScCut1 with other fungal cutinases indicated that ScCut1 contained the conserved motif G-Y-S-Q-G surrounding the active site serine as well as the aspartic acid and histidine residues of the cutinase active site. The gene was expressed in Pichia pastoris, and the recombinantly produced ScCut1 enzyme was purified to homogeneity by immobilized metal affinity chromatography exploiting a C-terminal His-tag translationally fused to the protein. The purified ScCut1 exhibited activity at acidic pH. The K(m) and V(max) values determined for pNP-butyrate esterase activity at pH 4.5 were 1.7 mM and 740 nkat mg⁻¹, respectively. Maximal activities were determined at between pH 4.7 and 5.2 and at between pH 4.1 and 4.6 with pNP-butyrate and tritiated cutin as the substrates, respectively. With both substrates, the enzyme was active over a broad pH range (between pH 3.0 and 7.5). Activity could still be detected at pH 3.0 both with tritiated cutin and with p-nitrophenyl butyrate (relative activity of 25 %) as the substrates. ScCut1 showed activity towards shorter (C2 to C3) fatty acid esters of p-nitrophenol than towards longer ones. Circular dichroism analysis suggested that the denaturation of ScCut1 by heating the protein sample to 80 °C was to a great extent reversible.

Serine protease inhibition attenuates rIL-12-induced GZMA activity and proinflammatory events by modulating the Th2 profile from estrogen-treated mice

Estrogen has potent immunomodulatory effects on proinflammatory responses, which can be mediated by serine proteases. We now demonstrate that estrogen increased the extracellular expression and IL-12-induced activity of a critical member of serine protease family Granzyme A, which has been shown to possess a novel inflammatory persona. The inhibition of serine protease activity with inhibitor 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride significantly diminished enhanced production of proinflammatory interferon-γ, IL-1β, IL-1α, and Granzyme A activity even in the presence of a Th1-inducing cytokine, IL-12 from splenocytes from in vivo estrogen-treated mice. Inhibition of serine protease activity selectively promoted secretion of Th2-specific IL-4, nuclear phosphorylated STAT6A, signal transducer and activator of transcription (STAT)6A translocation, and STAT6A DNA binding in IL-12-stimulated splenocytes from estrogen-treated mice. Inhibition with 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride reversed the down-regulation of Th2 transcription factors, GATA3 and c-Maf in splenocytes from estrogen-exposed mice. Although serine protease inactivation enhanced the expression of Th2-polarizing factors, it did not reverse estrogen-modulated decrease of phosphorylated STAT5, a key factor in Th2 development. Collectively, data suggest that serine protease inactivity augments the skew toward a Th2-like profile while down-regulating IL-12-induced proinflammatory Th1 biomolecules upon in vivo estrogen exposure, which implies serine proteases as potential regulators of inflammation. Thus, these studies may provide a potential mechanism underlying the immunomodulatory effect of estrogen and insight into new therapeutic strategies for proinflammatory and female-predominant autoimmune diseases.

Toward a Molecular Understanding of Adaptive Immunity: A Chronology, Part III

Early reports on T cell antigen receptor (TCR) signaling uncovered a rapid increase in intracellular calcium concentration and the activation of calcium-dependent protein kinase as necessary for T cell activation. Cytolytic T cell clones were instrumental in the discovery of intracellular cytolytic granules, and the isolation of the perforin and granzyme molecules as the molecular effectors of cell-mediated lysis of target cells via apoptosis. Cytolytic T cell clones and TCR cDNA clones were also instrumental for the generation of TCR transgenic animals, which provided definitive evidence for negative selection of self-reactive immature thymocytes. In addition, studies of TCR complex signaling of immature thymocytes compared with mature T cells were consistent with the interpretation that negative selection occurs as a consequence of the incapacity of immature cells to produce IL-2, resulting in cytokine deprivation apoptosis. By comparison, taking advantage of cloned TCRs derived from T cell clones reactive with male-specific molecules, using TCR transgenic mice it was possible to document positive selection of female thymocytes when the male-specific molecules were absent. Focusing on the molecular mechanisms of T cell "help" for the generation of antibody-forming cells following the path opened by the elucidation of the IL-2 molecule, several groups were successful in the identification, isolation, and characterization of three new interleukin molecules (IL-4, IL-5, and IL-6) that promote the proliferation and differentiation of B cells. In addition, the identification of a B cell surface molecule (CD40) that augmented B cell antigen receptor-stimulated proliferation and differentiation led to the discovery of a T cell activation surface molecule that proved to be the CD40-ligand, thus finally providing a molecular explanation for "linked or cognate" recognition when T cells and B cells interact physically. Accordingly, the decade after the generation of the first T cell clones saw the elucidation of the molecular mechanisms of T cell cytotoxicity and T cell help, thereby expanding the number of molecules responsible for adaptive T cell immunity.

Mycobacterium bovis BCG vaccine induces non-specific immune responses in Japanese flounder against Nocardia seriolae

Nocardiosis caused by Nocardia seriolae has been causing severe loss of fish production, so that an effective vaccine is urgently needed. Mycobacterium bovis BCG (BCG) is a live attenuated vaccine for tuberculosis, which is effective against various infectious diseases including nocardiosis in mammals. In this study, the protective efficacy of BCG against N. seriolae was evaluated in Japanese flounder Paralichthys olivaceus and antigen-specific immune responses induced in BCG vaccinated fish were investigated. Cumulative mortality of BCG-vaccinated fish was 21.4% whereas that of PBS-injected fish was 56.7% in N. seriolae challenge. However, gene expression level of IFN-γ was only slightly up-regulated in BCG-vaccinated fish after injection of N. seriolae antigen. In order to reveal non-specific immune responses induced by BCG vaccination, transcriptome of the kidney after BCG vaccination was investigated using oligo DNA microarray. Gene expression levels of antimicrobial peptides such as C-type and G-type lysozyme were significantly up-regulated after BCG vaccination. Consistently, BCG vaccination appeared to increase the bacteriolysis activity of the serum against Micrococcus luteus and N. seriolae. These results suggest that BCG-vaccinated Japanese flounder fight N. seriolae infection mainly by non-specific immune responses such as by the production of bacteriolytic lysozymes.

Improving immunogenicity and effectiveness of influenza vaccine in older adults

Aging is associated with a decline in immune function (immunosenescence) that leads to progressive deterioration in both innate and adaptive immune functions. These changes contribute to the subsequent increased risk for infectious diseases and their sequelae. Vaccination is the most effective and inexpensive public health strategy for prevention of infection, despite the decreased efficacy of vaccines in older adults due to immunosenescence. The rapid rise in the older adult population globally represents a great challenge for vaccination programs. This article first addresses the status of innate and adaptive immune functions in aging and then focuses on influenza vaccine. The development history of influenza vaccines, current status, and potential strategies to improve the immunogenicity and vaccine effectiveness in older adults are discussed.

Granzymes, cytotoxic granules and cell death: the early work of Dr. Jurg Tschopp

Within the powerful legacy left by Jurg Tschopp, we should not forget his early work that helped to elucidate the molecular pathways responsible for the clearance of virus-infected and transformed cells by cytotoxic T lymphocytes (CTL) and natural killer (NK) cells. Jurg's skilful biochemical approach formed a firm platform upon which the work of so many other biochemists, cell biologists and immunologists would come to rely. Jurg coined the shorthand term 'granzyme' to denote the individual members of a family of serine proteases sequestered in and secreted from the cytotoxic granules of CTL/NK cells. He was also one of the first to describe the lytic properties of purified perforin and to postulate the synergy of perforin and granzymes, which we now know to underpin target cell apoptosis. Jurg was a major protagonist in the debate that raged throughout the 1980's and early 1990's on the physiological relevance of the 'granule exocytosis' pathway. Ultimately, resolving this issue led Jurg and his colleagues to even greater and impactful discoveries in the broader field of apoptosis research. Jurg Tschopp ranks with other pioneers, particularly Gideon Berke, Chris Bleackley, Pierre Golstein, Pierre Henkart and Eckhard Podack for making seminal discoveries on our understanding of how the immune system eliminates dangerous cells.

Perforin pores in the endosomal membrane trigger the release of endocytosed granzyme B into the cytosol of target cells

How the pore-forming protein perforin delivers apoptosis-inducing granzymes to the cytosol of target cells is uncertain. Perforin induces a transient Ca²⁺ flux in the target, which triggers a damaged cell membrane repair process. As a consequence, both perforin and granzymes are endocytosed into enlarged endosomes, called gigantosomes. Here we show that perforin forms pores in the gigantosome membrane, allowing endosomal cargo, including granzymes, to be gradually released. After about 15 minutes, gigantosomes rupture, releasing their remaining content. Thus, perforin delivers granzymes by a two-step process that first involves transient pores in the cell membrane that trigger granzyme and perforin endocytosis and then pore formation in endosomes to trigger cytosolic release.

Granzyme A activates another way to die

Granzyme A (GzmA) is the most abundant serine protease in killer cell cytotoxic granules. GzmA activates a novel programed cell death pathway that begins in the mitochondrion, where cleavage of NDUFS3 in electron transport complex I disrupts mitochondrial metabolism and generates reactive oxygen species (ROS). ROS drives the endoplasmic reticulum-associated SET complex into the nucleus, where it activates single-stranded DNA damage. GzmA also targets other important nuclear proteins for degradation, including histones, the lamins that maintain the nuclear envelope, and several key DNA damage repair proteins (Ku70, PARP-1). Cells that are resistant to the caspases or GzmB by overexpressing bcl-2 family anti-apoptotic proteins or caspase or GzmB protease inhibitors are sensitive to GzmA. By activating multiple cell death pathways, killer cells provide better protection against a variety of intracellular pathogens and tumors. GzmA also has proinflammatory activity; it activates pro-interleukin-1beta and may also have other proinflammatory effects that remain to be elucidated.

The possible role of granzyme B in the pathogenesis of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a highly prevalent inflammatory lung condition characterized by airways disease and emphysema, and the precise mechanism of pathogenesis is poorly understood. The consistent features of COPD include protease-antiprotease imbalance, inflammation and accelerated aging caused by apoptosis or senescence. One family of molecules involved in all of these processes is the granzymes, serine proteases with the best-known member being granzyme B (GzmB). The majority of GzmB is released unidirectionally towards target cells, but GzmB can also be released nonspecifically and escape into the extracellular environment. GzmB is capable of cleaving extracellular matrix (ECM) proteins in vitro, and the accumulation of GzmB in the extracellular milieu during chronic inflammation in COPD could contribute to ECM degradation and remodelling and, consequently, the emphysematous phenotype in the lung. Preliminary studies suggest that increased GzmB expression is associated with increased COPD severity, and this may represent a promising new target for drug and biomarker discovery in COPD. In this paper, we review the potential pathogenic contributions of GzmB to the pathogenesis of COPD.

Immunosenescence Modulation by Vaccination

A decline in immune function is a hallmark of aging that leads to complicated illness from a variety of infectious diseases, cancer and other immune-mediated disorders, and may limit the ability to appropriately respond to vaccination. How vaccines might alter the senescent immune response and what are the immune correlates of protection will be addressed from the perspective of 1) stimulating a previously primed response as in the case of vaccines for seasonal influenza and herpes zoster, 2) priming the response to novel antigens such as pandemic influenza or other viruses, 3) vaccination against bacterial pathogens such as pneumococcus, and 4) altering the immune response to an endogenous protein as in the case of a vaccine against Alzheimer’s disease. In spite of the often limited efficacy of vaccines for older adults, influenza vaccination remains the only cost-saving medical intervention in this population. Thus, considerable opportunity exists to improve current vaccines and develop new vaccines as a preventive approach to a variety of diseases in older adults. Strategies for selecting appropriate immunologic targets for new vaccine development and evaluating how vaccines may alter the senescent immune response in terms of potential benefits and risks in the preclinical and clinical trial phases of vaccine development will be discussed.

Intracellular versus extracellular granzyme B in immunity and disease: challenging the dogma

The cytotoxic granzyme B (GrB)/perforin pathway has been traditionally viewed as a primary mechanism that is used by cytotoxic lymphocytes to eliminate allogeneic, virally infected and/or transformed cells. Although originally proposed to have intracellular and extracellular functions, upon the discovery that perforin, in combination with GrB, could induce apoptosis, other potential functions for this protease were, for the most part, disregarded. As there are 5 granzymes in humans and 11 granzymes in mice, many studies used perforin knockout mice as an initial screen to evaluate the role of granzymes in disease. However, in recent years, emerging clinical and biochemical evidence has shown that the latter approach may have overlooked a critical perforin-independent, pathogenic role for these proteases in disease. This review focuses on GrB, the most characterized of the granzyme family, in disease. Long known to be a pro-apoptotic protease expressed by cytotoxic lymphocytes and natural killer cells, it is now accepted that GrB can be expressed in other cell types of immune and nonimmune origin. To the latter, an emerging immune-independent role for GrB has been forwarded due to recent discoveries that GrB may be expressed in nonimmune cells such as smooth muscle cells, keratinocytes, and chondrocytes in certain disease states. Given that GrB retains its activity in the blood, can cleave extracellular matrix, and its levels are often elevated in chronic inflammatory diseases, this protease may be an important contributor to certain pathologies. The implications of sustained elevations of intracellular and extracellular GrB in chronic vascular, dermatological, and neurological diseases, among others, are developing. This review examines, for the first time, the multiple roles of GrB in disease pathogenesis.

Flow cytometric detection of perforin upregulation in human CD8 T cells

Perforin and granzymes work synergistically to induce apoptosis in target cells recognized by cytotoxic T lymphocytes. While perforin is readily detectable by flow cytometry in resting CD8 T cells, upregulation of perforin in activated cells is thought to require proliferation. However, perforin undergoes numerous conformational changes during its maturation, which may affect the ability of conventional antibodies to recognize newly synthesized perforin. Polychromatic flow cytometry was used to detect perforin and cytokine production following stimulation of ex vivo human CD8 T cells. Two different anti-perforin antibodies, clones B-D48 and deltaG9, were used to discriminate various forms of perforin after cellular activation. We provide evidence for the rapid upregulation of perforin protein, which may contribute to the ability of CD8 T cells to kill multiple targets over time. The deltaG9 clone recognizes the granule-associated conformation of perforin, while the B-D48 clone is able to detect perforin in multiple forms. Finally, we show there is variability in the ability of CD8 T cells to upregulate perforin. Human CD8 T cells are capable of new perforin production immediately following activation. This work defines a novel flow cytometric procedure that can be used to more completely assess the cytotoxic capacity of human CD8 T cells.

Granule enzyme exocytosis assay for cytotoxic T lymphocyte activation

Upon activation by specific target cells, cytotoxic T lymphocytes (CTL) release into the culture medium the content of cytoplasmic granules that contain serine esterases. The amount of enzyme released during CTL activation can be easily quantitated by spectrophotometric measurement of the colored product of the enzymatic degradation of a synthetic substrate. In the primary method presented here, CTL are activated with monoclonal antibodies prepared against the T cell receptor (TCR) complex, then activation is quantitated according to the amount of serine esterase released in the supernatant. Alternate protocols describe the activation of CTL by a combination of protein kinase C and calcium ionophores (a TCR-independent approach) and by the more conventional approach of target-cell mediation. In a third approach, beta-glucuronidase rather than esterase activity is measured, as this enzyme is also present in granules released upon CTL activation. This unit therefore includes a colorimetric assay for CTL-induced beta-glucuronidase activity employing the substrate phenolphthalein glucuronic acid as well as a corresponding automated fluorimetric assay employing the substrate 4-methylumbelliferyl-D-glucuronide. Finally, the quantitation of granule exocytosis resulting from cell damage or death induced by the activating agent, rather than CTL activation, is described.

Laughter up-regulates the genes related to NK cell activity in diabetes

To elucidate the sustainable effects of laughter on gene expression, we recruited type 2 diabetic patients who were in-patient for receiving self-management education and examined time-dependent regulation for gene expression by laughter. Two-day experiment was performed. On one day, the patients watched comic video and laughed together with hospital staffs. On the other day, they participated in an inpatient diabetes educational program. Blood samples were collected before and 1.5, 4 h after watching comic video or spending lecture time, and changes in gene expression were comprehensively analyzed by microarray technique. Of the 41,000 genes analyzed, the laughter relatively up-regulated 39 genes, among which, 27 genes were relatively increased in the expression for all the observation period after watching comic video. By functional classification of these genes, 14 genes were found to be related to natural killer cell activity. No genes were included that are directly involved in blood glucose regulation, though successive suppression of postprandial blood glucose levels was observed. These results suggest that the laughter influences the expression of many genes classified into immune responses, and may contribute to amelioration of postprandial blood glucose elevation through a modulation of NK cell activity caused by up-regulation of relating genes.

Influence of HLA-DR2 on perforin-positive cells in pulmonary tuberculosis

Perforin is one of the key effector molecules of cytotoxic T cells and natural killer cells. The influence of HLA-DRB1 alleles on peripheral blood perforin-positive CD4, CD8, CD16 and CD 56 cells was studied by flow cytometry. HLA-DRB1 typing was done in normal healthy subjects (NHS: n = 156) and patients with pulmonary tuberculosis (PTB: n = 102) by polymerase chain reaction-based sequence-specific oligonucleotide hybridization method. We observed a significantly decreased percentage of total perforin-positive cells (per(+)) (P = 0.0004); CD8(+)/Per(+) (P = 0.0005); CD16(+)/Per(+) (P = 0.05) and CD 56(+)/Per(+) cells (P = 0.001) in HLA-DR2-positive PTB patients compared to non-DR2 patients. Subtyping of HLA-DR2-positive subjects at the allelic level revealed that the percentage of CD8(+)/Per(+) cells did not differ among DRB1*1501 and DRB1*1502 patients while a trend towards a decreased percentage of CD16(+)/Per(+) and CD 56(+)/Per(+) cells was noticed in DRB1*1501 patients compared to DRB1*1502 patients. The present study suggests that HLA-DR2 may be associated with down-regulation of perforin-positive cytotoxic lymphocytes and natural killer cells in pulmonary tuberculosis.

Cytocidal activity of tumour necrosis factor: protection by protease inhibitors

The mechanism of the cytostatic and cytocidal activities of TNF was studied in human tumour cells. BT-20 breast and ME-180 cervical cancer cells were significantly growth-inhibited by TNF, but other cells were not. When protein synthesis was inhibited by cycloheximide, however, TNF was cytotoxic for all cells except BT-20 cells. This suggests that different mechanisms are responsible for the cytostatic and cytocidal activities of TNF. The sensitivity of different cell lines could not be correlated with the number or affinity of TNF receptors. Some protease inhibitors completely protected human and murine cells from TNF cytotoxicity. Inhibitors of chymotrypsin-like proteases were more effective than inhibitors of trypsin-like proteases. Reversible and irreversible inhibitors (such as alkylating compounds) were both protective. The cells were best protected when pretreated with inhibitors before the addition of TNF. When the protease inhibitors were removed the cells gradually lost their resistance to TNF cytotoxicity. The inhibitors did not interfere with the functioning of TNF-receptor complexes, since SK-MEL-109 melanoma cells treated with a protease inhibitor synthesized TNF-induced proteins. These findings suggest that a protease is involved in the cytocidal activity of TNF.

Cathepsin A is the major hydrolase catalyzing the intracellular hydrolysis of the antiretroviral nucleotide phosphonoamidate prodrugs GS-7340 and GS-9131

GS-7340 and GS-9131 {9-[(R)-2-[[(S)-[[(S)-1-(isopropoxycarbonyl)ethyl]amino]phenoxyphosphinyl]methoxy]-propyl]adenine and 9-(R)-4'-(R)-[[[(S)-1-[(ethoxycarbonyl)ethyl]amino]phenoxyphosphinyl]methoxy]-2'-fluoro-1'-furanyladenine, respectively} are novel alkylalaninyl phenyl ester prodrugs of tenofovir {9-R-[(2-phosphonomethoxy)propyl]adenine} (TFV) and a cyclic nucleotide analog, GS-9148 (phosphonomethoxy-2'-fluoro-2', 3'-dideoxydidehydroadenosine), respectively. Both prodrugs exhibit potent antiretroviral activity against both wild-type and drug-resistant human immunodeficiency virus type 1 strains and excellent in vivo pharmacokinetic properties. In this study, the main enzymatic activity responsible for the initial step in the intracellular activation of GS-7340 and GS-9131 was isolated from human peripheral blood mononuclear cells and identified as lysosomal carboxypeptidase A (cathepsin A [CatA]; EC 3.4.16.5). Biochemical properties of the purified hydrolase (native complex and catalytic subunit molecular masses of 100 and 29 kDa, respectively; isoelectric point [pI] of 5.5) matched those of CatA. Recombinant CatA and the isolated prodrug hydrolase displayed identical susceptibilities to inhibitors and identical substrate preferences towards a panel of tenofovir phosphonoamidate prodrugs. Incubation of both enzymes with 14C-labeled GS-7340 or [3H]difluorophosphonate resulted in the covalent labeling of identical 29-kDa catalytic subunits. Finally, following a 4-h incubation with GS-7340 and GS-9131, the intracellular concentrations of prodrug metabolites detected in CatA-negative fibroblasts were approximately 7.5- and 3-fold lower, respectively, than those detected in normal control fibroblasts. Collectively, these data demonstrate the key role of CatA in the intracellular activation of nucleotide phosphonoamidate prodrugs and open new possibilities for further improvement of this important class of antiviral prodrugs.

Granzyme K cleaves the nucleosome assembly protein SET to induce single-stranded DNA nicks of target cells

Although granzymes (Gzms) A- and B-induced cell death pathways have been defined, little is known about how other orphan Gzms function in CTL-mediated cytotoxicity. GzmK and A are tryptases among all the Gzms of humans and they are closely linked on the same chromosome. In this study, we showed that GzmK can be efficiently delivered into target cells with a cationic lipid protein transfection reagent Pro-Ject. We found human GzmK triggers rapid cell death independently of caspase activation. The features of death are characterized by rapid externalization of phosphatidylserine, nuclear morphological changes and single-stranded DNA nicks. GzmK hydrolyzes the nucleosome assembly protein SET in its recombinant and native forms or in intact cells. Cleavage of SET by GzmK abrogates its nucleosome assembly activity. After GzmK loading, SET and DNase NM23H1 rapidly translocate into the nucleus and SET is cleaved, where the nuclease activity of NM23H1 is activated to nick chromosomal DNA.

The unmet need in the elderly: Designing new influenza vaccines for older adults

Influenza is a serious illness and probably the single most important cause of excess disability and mortality during the winter months. In spite of limited efficacy in older adults, influenza vaccination is nevertheless a cost-saving medical intervention since it does reduce hospitalisation and death rates due to pneumonia, exacerbations of heart failure and, surprisingly, heart attacks and strokes. Yet hospitalisation and death rates for acute respiratory illnesses continue to rise in spite of widespread vaccination programs. As a person ages, the immune response to antigenic stimulation with the influenza virus shifts toward T helper type 2 cytokine production. This is associated with a relative reduction in cytotoxic T-cell activity and a reduced capacity to destroy infected host cells and clear the virus from infected lung tissue. Breakthrough strategies to improve the current influenza vaccines are required to avoid a crisis in health care. A targeted approach will develop vaccines that can reverse these age-related changes in T-cell responses, particularly the functions of cytotoxic T lymphocytes.

Suppression of adenoviral gene expression in the liver: role of innate vs adaptive immunity and their cell lysis mechanisms

BACKGROUND

Injection of adenoviral constructs causes liver infection prompting immunity, which suppress viral gene expression. Innate and adaptive immunity mediate these processes raising the question which pathways are the most prominent.

METHODS

Adenovirus expressing the beta-galactosidase (beta-gal) gene was injected into normal and immunodeficient mice. Elimination of beta-gal-expressing hepatocytes and increases in liver enzymes were assayed. Major histocompatibility complex (MHC) class I densities, perforin channel insertion and apoptosis by Fas and tumor necrosis factor (TNF)-alpha were assayed.

RESULTS

At high virus doses, suppression of viral gene expression was as efficient in immunodeficient as in normal mice, while at low doses effects of cytotoxic T lymphocytes (CTL) were demonstrable. Despite CTL priming and elimination of infected hepatocytes no liver injury is detected. Hepatocyte MHC I densities were able to trigger CTL granule exocytosis and perforin lysis in vitro but not in vivo. This is we show is because of decreased sensitivity of hepatocytes from infected mice to perforin and increased sensitivity to Fas and TNF-alpha lysis.

CONCLUSION

Effector cells of the innate immune system are exceedingly effective in suppressing adenoviral gene expression. Perforin-independent pathways, those mediated by TNF-alpha and Fas are very efficient in hepatocytes from virus-infected livers.

Granzymes in cytolytic lymphocytes--to kill a killer?

Granzymes (gzm) are major components of the granules of cytolytic lymphocytes, natural killer and cytotoxic T cells. Their generally accepted mode of action consists of their directed secretion towards a virus-infected or neoplastic target cell and perforin-dependent delivery to the target cell cytosol, where they engage in various actions resulting in target cell apoptosis. Here, based on observations of infection of gzmAxB(-/-) mice with ectromelia virus, mousepox, we propose an additional--and distinct--function for gzmA and B. In this model, gzm constitute one of the first lines of defence of immune cells against virus infection of immune cells themselves. Accordingly, endogenous gzm interfere with viral replication in cytolytic lymphocytes either directly, as a result of their proteolytic activity, leading to destruction of viral proteins, or indirectly, via: (i) processes akin to the caspase cascade when acting as effector molecules in the induction of target cell apoptosis; or (ii) their capacity to induce early inflammatory mediators. We discuss the predictions of the model in the light of available data.

Nuclear war: the granzyme A-bomb

Granzyme A, a serine protease in the cytotoxic granules of natural killer cells and cytotoxic T lymphocytes, induces caspase-independent cell death when introduced into target cells by perforin. Granzyme A induces single-stranded DNA damage as well as rapid loss of cell membrane integrity and mitochondrial transmembrane potential through unknown mechanisms. Granzyme A destroys the nuclear envelope by targeting lamins and opens up DNA for degradation by targeting histones. A special target of the granzyme A cell death pathway is an endoplasmic reticulum-associated complex, called the SET complex, which contains three granzyme A substrates, the nucleosome assembly protein SET, the DNA bending protein HMG-2, and the base excision repair endonuclease Ape1. The SET complex also contains the tumor suppressor protein pp32 and the granzyme A-activated DNase NM23-H1, which is inhibited by SET. Granzyme A cleavage of SET releases the inhibition and unleashes NM23-H1. Cleavage of Ape1 by granzyme A interferes with the ability of the target cell to repair itself. The novel cell death pathway initiated by granzyme A provides a parallel pathway for apoptosis, important in destroying targets that overexpress bcl-2 or are otherwise invulnerable to the caspases.

Cytotoxic granule-mediated apoptosis: unraveling the complex mechanism

The molecular details of cytotoxic granule-mediated apoptosis have been gleaned from the study of the effects of isolated granzymes and perforin on target cells. Recent evidence indicates that the physiological apoptosis-inducing form is a multi-component macro-complex consisting of cationic granule proteins non-covalently linked to the chondroitin-sulfate proteoglycan, serglycin.

Crystal structure of the apoptosis-inducing human granzyme A dimer

Granzyme A (GzmA) belongs to a family of trypsin-like serine proteases localized in cytoplasmic granules of activated lymphocytes and natural killer (NK) cells. In contrast to the related granzyme B (GzmB), GzmA forms a stable disulfide-linked homodimer and triggers target-cell death in a caspase-independent way. Limited proteolysis of a high-molecular-mass complex containing SET (also named putative HLA-associated protein II or PHAPII), PHAPI (pp32, leucine-rich acidic nuclear protein) and HMG2 by GzmA liberates NM23-H1, a Mg2+-dependent DNase that causes single-stranded breaks in nuclear DNA. By analyzing the dimeric GzmA structure at a resolution of 2.5 A, we determined the substrate-binding constraints and selective advantages of the two domains arranged as a unique functional tandem. The active sites of the two subunits point in opposite directions and the nearby noncatalytic surfaces can function as exosites, presenting substrates to the active site region of the adjacent partner in a manner analogous to staphylokinase or streptokinase, which present plasminogen to the cofactor-plasmin and cofactor-plasminogen complexes.

Organophosphorus pesticides markedly inhibit the activities of natural killer, cytotoxic T lymphocyte and lymphokine-activated killer: a proposed inhibiting mechanism via granzyme inhibition

We have previously found that diisopropyl methylphosphonate, an organophosphorus by-product generated during sarin synthesis in the Tokyo sarin disaster, significantly inhibited natural killer (NK) and cytotoxic T lymphocyte (CTL) activities. In the present study, to investigate whether organophosphorus pesticides (OPs) also affect NK and CTL activities, we firstly examined the effect of five OPs on human NK activity, and then the effect of Dimethyl 2,2-dichlorovinyl phosphate (DDVP), an OP on murine splenic NK, CTL and lymphokine-activated killer (LAK), and human LAK activities in vitro. To explore the underlying mechanism of decreased NK activity, we also investigated the effect of 4-(2-aminoethyl) benzenesulfonyl fluoride-HCl (p-ABSF), an inhibitor of serine proteases on NK, LAK and CTL activities, and the effect of DDVP on the activity of granzymes (serine proteases). We found that OPs significantly decreased human NK activity in a dose-dependent manner, but the degree of decrease in NK activity differed among the OPs investigated, and that DDVP significantly decreased NK, LAK and CTL activities in a dose-dependent manner, but the degree of decrease in these activities differed. p-ABSF showed a similar inhibitory pattern to DDVP, and had an additive inhibitory effect with DDVP on NK, LAK and CTL activities. We also found that DDVP significantly inhibited granzyme activity in a dose-dependent manner. These findings indicate that OPs significantly decrease NK, LAK and CTL activities in vitro via granzyme inhibition.

Elevation of cytotoxic lymphocyte gene expression is predictive of islet allograft rejection in nonhuman primates

Hyperglycemia and increased insulin requirements are indicators of ongoing islet allograft rejection, but there are no methods to predict or confirm rejection. Elevation of cytotoxic lymphocyte (CL) gene expression in peripheral blood (PB) has been correlated with renal allograft rejection in humans, but no published study has assessed the utility of monitoring these markers as predictors of rejection before the onset of clinical symptoms. We have established quantitative real-time PCR methods to determine the levels of mRNA transcripts for the CL genes granzyme B (GB), perforin, and fas ligand in blood samples from rhesus and cynomolgus monkeys. Four rhesus monkeys with long-term islet allograft function were studied. Antirejection (anti-CD154) therapy was discontinued, and weekly PB samples were obtained to determine whether the levels of mRNA transcripts for CL genes correlated with and/or were predictive of islet allograft rejection, defined as a loss of C-peptide production. For all monkeys, elevation of CL gene expression preceded rejection by 83--197 days, with GB as the best predictor. Elevated mRNA levels were sustained for 2--2.5 months in three of four animals and 1 month in the other, thus suggesting that the testing of these parameters may have practical applications in clinical islet cell transplantation.

Heterogeneity of channel catfish CTL with respect to target recognition and cytotoxic mechanisms employed

Two types of catfish alloantigen-dependent cytotoxic T cells were cloned from PBL from a fish immunized in vivo and stimulated in vitro with the allogeneic B cell line 3B11. Because these are the first clonal cytotoxic T cell lines derived from an ectothermic vertebrate, studies were undertaken to characterize their recognition and cytotoxic mechanisms. The first type of CTL (group I) shows strict alloantigen specificity, i.e., they specifically kill and proliferate only in response to 3B11 cells. The second type (group II) shows broad allogeneic specificity, i.e., they kill and proliferate in response to several different allogeneic cells in addition to 3B11. "Cold" target-inhibition studies suggest that group II CTL recognize their targets via a single receptor, because the killing of one allotarget can be inhibited by a different allotarget. Both types of catfish CTL form conjugates with and kill targets by apoptosis. Killing by Ag-specific cytotoxic T cells (group I) was completely inhibited by treatment with EGTA or concanamycin A, and this killing is sensitive to PMSF inhibition, suggesting that killing was mediated exclusively by the secretory perforin/granzyme mechanism. In contrast, killing by the broadly specific T cytotoxic cells (group II) was only partially inhibited by either EGTA or concanamycin A, suggesting that these cells use a cytotoxic mechanism in addition to that involving perforin/granzyme. Consistent with the presumed use of a secretory pathway, both groups of CTL possess putative lytic granules. These results suggest that catfish CTL show heterogeneity with respect to target recognition and cytotoxic mechanisms.

Granzymes A and B directly cleave lamins and disrupt the nuclear lamina during granule-mediated cytolysis

Cytotoxic T lymphocytes (CTL) induce apoptosis by engaging death receptors or by exocytosis of cytolytic granules containing granzyme (Gzm) proteases and perforin. The lamins, which maintain the structural integrity of the nuclear envelope, are cleaved by caspases during caspase-mediated apoptosis. Although death receptor engagement and GzmB activate caspases, CTL also induce apoptosis during caspase blockade. Both GzmA and GzmB directly and efficiently cleave laminB in vitro, in situ in isolated nuclei and in cells loaded with perforin and Gzms, even in the presence of caspase inhibitors. LaminB is cleaved by GzmA at concentrations of 3 nM, but GzmB is 50 times less active. GzmA cuts laminB at R392; GzmB cuts at the caspase VEVD231 site. Characteristic laminB fragments generated by Gzm proteolysis also are observed during CTL lysis, even in the presence of caspase inhibitors or in cells overexpressing bcl-2. Lamins A/C are direct substrates of GzmA, but not GzmB. GzmA and GzmB therefore directly target critical caspase substrates in caspase-resistant cells.

Induction of rapid histone degradation by the cytotoxic T lymphocyte protease Granzyme A

The cytotoxic T lymphocyte protease granzyme A induces caspase-independent cell death in which DNA single-strand nicking is observed instead of oligonucleosomal fragmentation. Granzyme A is a specific tryptase that concentrates in the nucleus of targeted cells and synergistically enhances DNA fragmentation induced by the caspase activator granzyme B. Here we show that granzyme A treatment of isolated nuclei enhances DNA accessibility to exogenous endonucleases. In vitro and after cell loading with perforin, GrnA completely degrades histone H1 and cleaves core histones into approximately 16-kDa fragments. Histone digestion provides a mechanism for unfolding compacted chromatin and facilitating endogenous DNase access to DNA during T cell and natural killer cell granule-mediated apoptosis.

Heat-shocked A20 lymphoma cells fail to induce degranulation of cytotoxic T lymphocytes: possible mechanism of resistance

A20 lymphoma cells were subjected to heat shock for 2 h at 42 and 43 +/- 0.1 degrees C and then evaluated at 37 degrees C for sensitivity to lysis by intact allo-specific cytotoxic T lymphocytes (CTLs), perforin-containing granules isolated from CTLs, and Fas-mediated apoptosis. Heat shock at 42 degrees C caused little change in sensitivity of the lymphoma cell line to lysis by intact CTLs or their isolated cytotoxic granules, but caused increased sensitivity to Fas-mediated apoptosis. However, A20 cells shocked at 43 degrees C declined significantly in sensitivity to lysis by intact CTLs, while remaining very sensitive to perforin granules and to Fas-mediated apoptosis. Expression of the inducible heat shock protein was observed in A20 cells incubated at 43 degrees C, but not in those incubated at 42 degrees C, suggesting a role for heat shock proteins. Furthermore, A20 cells shocked at 43 degrees C did not provoke degranulation and secretion of granzymes by antigen-specific CTLs, although formation of CTL-target conjugates and levels of MHC class I molecules remained unchanged. These observations demonstrate that hyperthermia or febrile conditions may reduce susceptibility of target cells to CTL attack due to failure of antigen presentation and the inability of CTLs to recognize heat stressed targets, thus enabling targets to escape CTL attack.

The by-products generated during sarin synthesis in the Tokyo sarin disaster induced inhibition of natural killer and cytotoxic T lymphocyte activity

More than 5000 passengers on Tokyo subway trains were injured by the nerve gas, sarin and its by-products. Analysis of phosphor-carrying metabolites of sarin and its by-products in urine samples from the victims suggested that they were exposed not only to sarin, but also by-products generated during sarin synthesis, i.e. diisopropyl methylphosphonate (DIMP) and diethyl methylphosphonate (DEMP). We suspected genetic after-effects due to sarin by-products, thus, we checked the frequency of sister chromatid exchange (SCE) and found that SCE was significantly higher in the victims than in a control group, and that DIMP and DEMP significantly induced human lymphocyte SCE in vitro. In the present study, to explore whether DIMP and DEMP, which induced a high frequency of SCE of lymphocytes, also affected the lymphocyte functions, we examined the effect of DIMP and DEMP on splenic natural killer (NK) and splenic cytotoxic T lymphocyte (CTL) activity in mice, and NK activity of human lymphocytes in vitro. We found that DIMP and DEMP significantly inhibited NK and CTL activity in a dose-dependent manner. The inhibition induced by DIMP was stronger than that by DEMP. The effect of DIMP and DEMP on the splenic NK activity of mice was stronger than on the splenic CTL activity, and the human lymphocytes is more sensitive to DIMP and DEMP than the splenocytes of mice.

Effect of 1,25(OH)(2)-vitamin D(3) on the activation of natural killer cells: role of protein kinase C and extracellular calcium

As a first approach for studying the implication of PKC and the steroid hormone 1,25(OH)(2)-vitamin D(3) [1,25(OH)(2)D(3)] on natural killer cell (NK) activity, we analyzed in the YT NK cell line the expression of PKC isoforms and the effects of 1, 25(OH)(2)D(3) on BLT-esterase (a marker of NK lytic granules) activity. Western blot and RT-PCR showed a greater extent of PKC alpha, beta, delta, zeta, epsilon, theta, and lambda and lower levels of PKC mu and eta. In a dose-dependent manner 1, 25(OH)(2)D(3) induced significant increases in BLT-esterase and PKC activities and the stimulatory effect on BLT-esterase activity was mimicked and blocked, respectively, by the PKC activator phorbol ester PMA and PKC inhibitors (H7, PKC(19-36), and N-myristoylated PKC(19-31) peptides). Moreover, the effects of 1,25(OH)(2)D(3) on BLT-esterase could be blocked in a Ca(2+)-free (+EGTA) medium and mimicked by the Ca2+ ionophore A23187. The results suggest that 1, 25(OH)(2)D(3) is a stimulatory factor of NK activity acting through a mechanism involving PKC and extracellular Ca2+.

Serine protease inhibitor TPCK prevents Taxol-induced cell death and blocks c-Raf-1 and Bcl-2 phosphorylation in human breast carcinoma cells

The mechanism of Taxol-induced apoptosis was investigated in MCF-7 human breast carcinoma cells. Taxol-induced apoptosis was associated with phosphorylation of both c-Raf-1 and Bcl-2 and activation of ERK and JNK MAP kinases. The serine protease inhibitor N-tosyl-L-phenylalanine chloromethyl ketone (TPCK) effectively blocked apoptosis, but N-p-tosyl-L-lysine chloromethyl ketone (TLCK), another serine protease inhibitor, was without effect. TPCK treatment also prevented phosphorylation of c-Raf-1 and Bcl-2 in response to Taxol treatment. The serine protease inhibitor did not alter JNK activity, but it enhanced Taxol-induced activation of ERK1/2. Treatment of cells with the inhibitor of MEK activation, PD98059, prevented Taxol-induced ERK activation both in the presence and absence of TPCK, but did not influence survival of either Taxol- or Taxol plus TPCK-treated cells. In addition, PD98059 had no effect on c-Raf-1 or Bcl-2 phosphorylation. Thus, while the Taxol-induced phosphorylations of c-Raf-1 and Bcl-2 proteins appear to be coupled, these events can be disassociated from ERK1/2 activation. In summary, these findings suggest that phosphorylation of c-Raf-1 and Bcl-2, but not ERK1/2, are important signaling events in Taxol-induced apoptosis of MCF-7 breast cancer cells and that a TPCK inhibitable protease(s) is required for these processes.

Granzyme A initiates an alternative pathway for granule-mediated apoptosis

Granzyme (gzm) B-deficient cytotoxic lymphocytes (CTL) have a severe defect in the rapid induction of target cell apoptosis that is almost completely corrected by prolonged incubation of the CTL effectors and their targets. We show in this report that perforin-dependent, gzmB-independent cytotoxicity is caused by gzmA (or tightly linked genes). CTL deficient for gzmA and gzmB retain normal perforin function, but these CTL have a cytotoxic defect in vivo that is as severe as perforin-deficient CTL. Collectively, these results suggest that perforin provides target cell access and/or trafficking signals for the gzms, and that the gzms themselves deliver the lethal hits. The gzmA pathway appears to function independently from gzmB and may therefore provide a critical "back-up" system when gzmB is inhibited in the target cell.

Granzyme A loading induces rapid cytolysis and a novel form of DNA damage independently of caspase activation

Cytotoxic lymphocytes trigger apoptosis by releasing perforin and granzymes (Grn). GrnB activates the caspase apoptotic pathway, but little is known about GrnA-induced cell death. Perforin was used to load recombinant GrnA and GrnB and enzymatically inactive variants into target cells. GrnA induces single-strand DNA breaks that can be labeled with Klenow polymerase and visualized on alkaline gels. GrnA-induced DNA damage but not cytolysis requires GrnA proteolysis. GrnA-induced membrane perturbation, nuclear condensation, and DNA damage are unimpaired by caspase blockade. GrnA fails to induce cleavage of caspase-3, lamin B, rho-GTPase, or PARP. GrnA-induced cytotoxicity and cleavage of PHAP II, a previously identified GrnA substrate, are unimpaired in Jurkat cells that overexpress bcl-2. Therefore, GrnA activates a novel apoptotic pathway.