Cloning of a cDNA for a T cell-specific serine protease from a cytotoxic T lymphocyte

Extracellular granzyme A in amniotic fluid is elevated in the presence of sterile intra-amniotic inflammation in preterm prelabor rupture of membranes

INTRODUCTION

To determine the levels of granzyme A in amniotic fluid in pregnancies complicated by preterm prelabor rupture of membranes (PPROM), based on the presence of microbial invasion of the amniotic cavity (MIAC) and/or intra-amniotic inflammation (IAI).

METHODS OF STUDY

A total of 166 women with singleton pregnancies complicated by PPROM were included. Amniocentesis was performed at the time of admission and assessments of MIAC (using both cultivation and non-cultivation techniques) and IAI (interleukin-6 in amniotic fluid) were performed on all subjects. Based on the presence/absence of MIAC and IAI, the women were further divided into the following subgroups: intra-amniotic infection, sterile IAI, colonization, and absence of both MIAC and IAI. Amniotic fluid granzyme A levels were assessed using ELISA.

RESULTS

Women with MIAC had lower levels of granzyme A in the amniotic fluid than women without this condition (with MIAC: median 15.9 pg/mL vs. without MIAC: median 19.9 pg/mL, p = .03). Women with sterile IAI had higher amniotic fluid granzyme A levels than women with intra-amniotic infection, colonization and women with the absence of either MIAC or IAI (intra-amniotic infection: median 15.6 pg/mL; sterile IAI: median 31.8 pg/mL; colonization: median 16.9 pg/mL; absence of both MIAC and IAI: median 18.8 pg/mL; p = .02).

CONCLUSIONS

The presence of sterile IAI was associated with elevated levels of granzyme A in amniotic fluid.

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.

A quarter century of granzymes

Granzymes (Grs) were discovered just over a quarter century ago. They are produced by cytotoxic T cells and natural killer cells and are released upon interaction with target cells. Intensive biochemical, genetic, and biological studies have been performed in order to study their roles in immunity and inflammation. This review summarizes research on the family of Grs.

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 cell, which triggers a process to repair the damaged cell membrane. As a consequence, both perforin and granzymes are endocytosed into enlarged endosomes called 'gigantosomes'. Here we show that perforin formed pores in the gigantosome membrane, allowing endosomal cargo, including granzymes, to be gradually released. After about 15 min, gigantosomes ruptured, releasing their remaining content. Thus, perforin delivers granzymes by a two-step process that involves first transient pores in the cell membrane that trigger the endocytosis of granzyme and perforin 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.

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.

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.

Transcriptional Profiling of Hematologic Malignancies with a Low-Density DNA Microarray

Background: High-density microarrays are powerful tools for expression analysis of thousands of genes simultaneously; however, experience with low-density microarrays in gene expression studies has been limited.

Methods: We developed an optimized procedure for gene expression analysis based on a microarray containing 538 oligonucleotides and used this procedure to analyze neoplastic cell lines and whole-blood samples from healthy individuals and patients with different hematologic neoplasias. Hierarchical clustering and the Welch t-test with adjusted P values were used for data analysis.

Results: This procedure detects 0.2 fmol of mRNA and generates a linear response of 2 orders of magnitude, with CV values of <20% for hybridization and label replicates. We found statistically significant differences between Jurkat and U937 cell lines, between blood samples from 15 healthy donors and 59 chronic lymphocytic leukemia (CLL) samples, and between 6 acute myeloid leukemia patients and 4 myelodysplastic syndrome patients. A classification system constructed from the expression data predicted healthy or CLL status from a whole-blood sample with a 97% success rate.

Conclusion: Transcriptional profiling of whole-blood samples was carried out without any cellular or sample manipulation before RNA extraction. This gene expression analysis procedure uncovered statistically significant differences associated with different hematologic neoplasias and made possible the construction of a classification system that predicts the healthy or CLL status from a whole-blood sample.

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.

Impaired electroretinogram (ERG) response in apolipoprotein E-deficient mice

PURPOSE

We investigated the effects of 35 weeks of a cholesterol diet in apolipoprotein E (apoE)-deficient mice on their ERG response.

METHODS

C57BL/6J and apoE-deficient mice were fed regular mouse chow (C57-R and ApoE-R, respectively) or a cholesterol-containing diet (C57-C and ApoE-C, respectively). Retinal function was assessed by dark-adapted electroretinography (ERG). Retina tissue was also analyzed by immunohistochemical staining and nucleic acid array expression analysis performed by gene array technology.

RESULTS

ApoE-C mice had diminished a- and b-wave amplitudes (60.7% +/- 8.4% (p < 0.005) and 44.8% +/- 10% (p < 0.005) of control values, respectively). Gene expression profiling revealed upregulation of several pro-apoptotic genes. Furthermore, immunohistochemistry showed increased Bax immunoreactivity.

CONCLUSIONS

In the hypercholesterolemic mice, we demonstrated a loss of ERG response and induction of apoptotic activity at the gene and protein levels. Our current and previous findings suggest that cholesterol metabolism plays an important role in retinal function.

Trypsinogen hL expressed in the human lung is a new member of the trypsinogen family

Molecular cloning of cDNA encoding a new member of the trypsinogen family, named trypsinogen hL, was carried out by PCR using human lung cDNAs as templates. The primary structure of trypsinogen hL was found to be a prepro-protein and a catalytic triad, 64His, 108Asp and 201Ser. It was also found that trypsinogen hL is specifically expressed in the human lung, the expression level being 30-times higher than those in other tissues tested. A phylogenic tree analysis showed that trypsinogen hL is a new member of the trypsinogen family, a family of serine protease family proteins.

Dipeptidyl peptidase I: importance of progranzyme activation sequences, other dipeptide sequences, and the N-terminal amino group of synthetic substrates for enzyme activity

The broadly reactive cysteine protease dipeptidyl peptidase I (DPPI, cathepsin C) is thought to activate all progranzymes (zymogens of lymphocyte serine proteases) to form mature granzymes. We synthesized dipeptide 7-amino-4-methylcoumarin (AMC) substrates containing progranzyme activation sequences and showed that they were efficiently hydrolyzed by DPPI. However, DPPI will not hydrolyze Ile-Ile-AMC, the N-terminal dipeptide sequence found in mature granzymes. Introduction of the nonphysiological homophenylalanine (Hph) residue at P1 resulted in the best substrate Ala-Hph-AMC for DPPI (k(cat)/K(m)=9,000,000M(-1)s(-1)). The charged N-terminal amino group of the substrate was essential and replacement of the NH(2) group with OH or NH(CH(3)) in Gly-Phe-AMC reduced the k(cat)/K(m) value by two to three orders of magnitude. A hydrazide azaglycine analog, NH(2)NHCO-Phe-AMC, was not hydrolyzed at pH 5.5, but underwent slow hydrolysis at lower pHs where the amino group is partially protonated. DPPI also failed to hydrolyze NH(2)COCH(2)-Phe-AMC, where the NH(2) group is unprotonated. The results reported in this paper should be useful in the design of better DPPI inhibitors to block granzyme maturation and granzyme-dependent apoptosis.

Noncaspase proteases in apoptosis

Biochemical and genetic analysis of apoptosis has determined that intracellular proteases are key effectors of cell death pathways. In particular, early studies have pointed to the primacy of caspase proteases as mediators of execution. More recently, however, evidence has accumulated that noncaspases, including cathepsins, calpains, granzymes, and the proteasome complex, also have roles in mediating and promoting cell death. An important goal is to understand the importance of distinct noncaspases in various forms of apoptosis, and to determine whether pathways mediated by noncaspase proteases intersect with those mediated by caspases. In this review the roles of noncaspase proteases in the biochemistry of apoptosis will be discussed.

Application of an improved cDNA competition technique to identify prostate cancer-associated gene

A technique to improve cDNA library screening was developed by using mixed probes derived from two closely related cDNA populations of high-metastatic MAT-LyLu and low-metastatic AT-1 Dunning R3227 rat prostate cancer sublines. The technique required the generation of a cDNA library from each subline followed by polymerase chain reaction (PCR) amplification of the cDNA insert population. The PCR products derived from the first library were radiolabeled and mixed with an excess amount of PCR products from the second library. The mixture and an excess amount of both the lambda and pBluescript DNA were used as a probe to screen the first cDNA library. This mixed probe (designated the competition probe) differentially cross-hybridized with the plaque lift of the screened first cDNA library. Weak radioactive signals indicated the cross-hybridization of cDNA sequences common to the competition probe mixture and the first cDNA library, whereas strong signals implied unhybridized unique or abundant cDNA sequences in the first cDNA library. The reproducibility of this technique was confirmed by showing that the full-length cDNA clones were associated with the phenotype of the screened first cell line. The isolated clones were characterized as rat nucleolar protein, rat mitochondrial genes coding for 16S and 12S rRNAs, and rat tRNAs specific for valine and phenyl-alanine. This result is consistent with the fact that the first cell line, MAT-LyLu, is metabolically more active than are AT-1 cells because of higher gene dosage or amplification of nucleolar and mitochondrial RNA and its associated genes. Another clone which had a strong signal represented a novel gene associated with the MAT-LyLu cancer phenotype.

CD8+TCR+ and CD8+TCR- cells in whole bone marrow facilitate the engraftment of hematopoietic stem cells across allogeneic barriers

Although purified hematopoietic stem cells (HSC) are sufficient to engraft irradiated allogeneic recipients, bone marrow (BM) contains other cells that facilitate engraftment. Here, several candidate facilitators were tested by cotransplantation with HSC. Both TCR+ and TCR- CD8alpha+ BM subpopulations have facilitative potential. CD8+TCR+ cells are typical T lymphocytes. CD8+TCR- facilitators are CD3 , not CD3+, have a granular morphology, and are CD8beta- and CD11c+; they share phenotypic characteristics with CD8(alpha)alpha lymphoid dendritic cells and veto cells. We also demonstrate that lytic function is nqt necessary for facilitation and that the CD8alpha molecule is either important for facilitation or in the development of facilitators.

Identification of two serine residues involved in catalysis by fatty acid amide hydrolase

Fatty acid amide hydrolase is an integral membrane protein that hydrolyzes a novel and growing class of neuromodulatory fatty acid molecules, including anandamide, 2-arachidonyl glycerol, and oleamide. This activity is inhibited by serine and cysteine reactive agents, suggesting that the active site contains a serine or cysteine residue. Therefore serine and cysteine residues were mutated to alanine and the effects on activity were determined. Mutants were prepared using site-directed mutagenesis methods and expressed in COS-7 cells. Serine mutations S217A and S241A completely abolished enzymatic activity. Mutants S152A and C249A had no effect on activity, while S218A showed a slight decrease in activity. To confirm these results biochemically, the mutant enzymes were reacted with the irreversible inhibitor [(14)C]-diisopropyl fluorophosphate. All of the mutants except S217A and S241A were labeled. We therefore confirm that fatty acid amide hydrolase is a serine hydrolase and propose that both Ser-217 and Ser-241 are essential for enzyme activity.

cDNA cloning and expression of a novel serine protease in the mouse brain

A cDNA for a novel serine protease, termed brain type granzyme K (B-GRK) was cloned from the mouse brain. The cDNA codes a protein similar to granzyme K (GRK) but completely different at the N-terminus. Genomic Southern and PCR analysis of the gene suggests B-GRK is the alternative transcription form of GRK. B-GRK and GRK have a different organ-specific expression pattern: B-GRK is expressed in the brain, while GRK is expressed in the spleen. The recombinant fusion protein was detected in the neuro2a cells transfected with a plasmid containing B-GRK sequence. The mRNA for B-GRK/GRK was detected in cerebral cortex, hippocampus and diencephalon of the mouse brain. In situ hybridization for B-GRK/GRK revealed that several regions in the forebrain and hypothalamus express the mRNA. Developmental analysis showed that in the prenatal stage, the mRNA was expressed also in pituitary and pineal body in addition to the brain.

Gammadelta receptor bearing T cells in scleroderma: enhanced interaction with vascular endothelial cells in vitro

In view of the documented perivascular mononuclear cell infiltration in the involved organs in scleroderma (SSc) and the reported accumulation of gammadelta-T cells in SSc skin and lung, we evaluated gammadelta-T cell interaction with endothelial cells (EC) in vitro. gammadelta- and alphabeta-T cells were isolated from BPMN of SSc patients with early diffuse disease and of matched control subjects by an immunomagnetic method after stimulation with mycobacterium lysate and interleukin-2 for 2 weeks. Lymphocyte adhesion, proliferation, and cytotoxicity to EC were investigated. SSc gammadelta-T cells adhered to cultured EC and proliferated at higher rates than control cells. Furthermore, significant EC cytotoxicity by SSc gammadelta was seen. The cytotoxicity was blocked by addition of anti-gammadelta-TCR antibody and by anti-granzyme A antibody but not by anti-MHC class I and II antibodies. Expression of granzyme A mRNA was seen in five/five SSc gammadelta-T cells and in one/five control cells. alphabeta-T cells from both SSc and control subjects were significantly less interactive with EC than gammadelta-T cells. The data demonstrate EC recognition by SSc gammadelta-T cells and propose gammadelta-T cells as a possible effector cell type in the immune pathogenesis of SSc.

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.

A Role for Heat Shock Protein 27 in CTL-Mediated Cell Death

CTL exocytosis of granules containing perforin and granzyme proteases induces apoptotic cell death. Either granzyme A or B can act with perforin to trigger apoptosis. Granzyme B activates a ubiquitous apoptotic cascade induced by caspase cleavage, but the granzyme A pathway is largely unknown. Using affinity chromatography with recombinant mutant inactive granzyme A, we previously isolated two granzyme A-binding proteins, PHAP (putative HLA-associated protein) I and II. PHAP II, a substrate of granzyme A, is degraded within minutes of CTL attack. Two additional cytoplasmic proteins of 27 and 53 kDa bind strongly to the mutant granzyme A column, requiring 6 M urea to elute. Sequencing identified these as the monomer and dimer of hsp27, a small heat shock protein up-regulated by stress and cellular activation. Hsp27 coprecipitates with granzyme A from cytoplasmic lysates and is not a substrate of the enzyme. Hsp27 translocates to the detergent-insoluble fraction of target cells and relocalizes from diffuse cytoplasmic staining to long filamentous fibers, especially concentrated in a perinuclear region, within minutes of CTL attack. Hsp27 may participate in morphologic changes during granule-mediated lysis. Low or absent levels of hsp27 expression in T lymphocytes, even after heat shock, may play a role in CTL resistance to granule-mediated lysis.

Dual mechanisms of apoptosis induction by cytotoxic lymphocytes

Cytotoxic T lymphocytes and natural killer cells together comprise the means by which the immune system detects and rids higher organisms of virus-infected or transformed cells. Although differing considerably in the way they detect foreign or mutated antigens, these cells utilize highly analogous mechanisms for inducing target cell death. Both types of effector lymphocytes utilize two principal contact-dependent cytolytic mechanisms. The first of these, the granule exocytosis mechanism, depends on the synergy of a calcium-dependent pore-forming protein, perforin, and a battery of proteases (granzymes), and it results in penetration by effector molecules into the target cell cytoplasm and nucleus. The second, which requires binding of FasL (CD95L) on the effector cell with trimeric Fas (CD95) molecules on receptive target cells, is calcium independent and functions by generating a death signal at the inner leaflet of the target cell membrane. Exciting recent developments have indicated that both cytolytic mechanisms impinge on an endogenous signaling pathway that is strongly conserved in species as diverse as helminths and humans and dictates the death or survival of all cells.

Natural Killer and B-Lymphoid Potential in CD34+ Cells Derived From Embryonic Stem Cells Differentiated in the Presence of Vascular Endothelial Growth Factor

Differentiation of totipotent mouse embryonic stem (ES) cells to various lymphohematopoietic cells is an in vitro model of the hematopoietic cell development during embryogenesis. To understand this process at cellular levels, differentiation intermediates were investigated. ES cells generated progeny expressing CD34, which was significantly enhanced by vascular endothelial growth factor (VEGF). The isolated CD34+ cells were enriched for myeloid colony-forming cells but not significantly for erythroid colony-forming cells. When cultured on OP9 stroma cells in the presence of interleukin-2 and interleukin-7, the CD34+ cells developed two types of B220+ CD34−lymphocytes: CD3− cytotoxic lymphocytes and CD19+ pre-B cells, and such lymphoid potential was highly enriched in the CD34+ population. Interestingly, the cytotoxic cells expressed the natural killer (NK) cell markers, such as NKR-P1, perforin, and granzymes, classified into two types, one of which showed target specificity of NK cells. Thus, ES cells have potential to generate NK-type cytotoxic lymphocytes in vitro in addition to erythro-myeloid cells and pre-B cells, and both myeloid and lymphoid cells seem to be derived from the CD34+intermediate, on which VEGF may play an important role.

Natural Killer and B-Lymphoid Potential in CD34+ Cells Derived From Embryonic Stem Cells Differentiated in the Presence of Vascular Endothelial Growth Factor

Differentiation of totipotent mouse embryonic stem (ES) cells to various lymphohematopoietic cells is an in vitro model of the hematopoietic cell development during embryogenesis. To understand this process at cellular levels, differentiation intermediates were investigated. ES cells generated progeny expressing CD34, which was significantly enhanced by vascular endothelial growth factor (VEGF). The isolated CD34+ cells were enriched for myeloid colony-forming cells but not significantly for erythroid colony-forming cells. When cultured on OP9 stroma cells in the presence of interleukin-2 and interleukin-7, the CD34+ cells developed two types of B220+ CD34−lymphocytes: CD3− cytotoxic lymphocytes and CD19+ pre-B cells, and such lymphoid potential was highly enriched in the CD34+ population. Interestingly, the cytotoxic cells expressed the natural killer (NK) cell markers, such as NKR-P1, perforin, and granzymes, classified into two types, one of which showed target specificity of NK cells. Thus, ES cells have potential to generate NK-type cytotoxic lymphocytes in vitro in addition to erythro-myeloid cells and pre-B cells, and both myeloid and lymphoid cells seem to be derived from the CD34+intermediate, on which VEGF may play an important role.

Circulating CD8 T Lymphocytes in Human Immunodeficiency Virus-Infected Individuals Have Impaired Function and Downmodulate CD3ζ, the Signaling Chain of the T-Cell Receptor Complex

Although human immunodeficiency virus (HIV)-infected subjects without acquired immunodeficiency syndrome have a high frequency of HIV-specific CD8 T lymphocytes, freshly isolated lymphocytes frequently lack detectable HIV-specific cytotoxicity. However, this effector function becomes readily apparent after overnight culture. To investigate reasons for T-cell dysfunction, we analyzed T-cell expression of the cytolytic protease granzyme A and of CD3ζ, the signaling component of the T-cell receptor complex. An increased proportion of CD4 and CD8 T cells from HIV-infected donors contain granzyme A, consistent with the known increased frequency of activated T cells. In 28 HIV-infected donors with mild to advanced immunodeficiency, a substantial fraction of circulating T cells downmodulated CD3ζ (fraction of T cells expressing CD3ζ, 0.74 ± 0.16 v 1.01 ± 0.07 in healthy donors; P < .0000005). CD3ζ expression is downregulated more severely in CD8 than CD4 T cells, decreases early in infection, and correlates with declining CD4 counts and disease stage. CD3ζ expression increases over 6 to 16 hours of culture in an interleukin-2–dependent manner, coincident with restoration of viral-specific cytotoxicity. Impaired T-cell receptor signaling may help explain why HIV-specific cytotoxic T lymphocytes fail to control HIV replication.

Circulating CD8 T Lymphocytes in Human Immunodeficiency Virus-Infected Individuals Have Impaired Function and Downmodulate CD3ζ, the Signaling Chain of the T-Cell Receptor Complex

Although human immunodeficiency virus (HIV)-infected subjects without acquired immunodeficiency syndrome have a high frequency of HIV-specific CD8 T lymphocytes, freshly isolated lymphocytes frequently lack detectable HIV-specific cytotoxicity. However, this effector function becomes readily apparent after overnight culture. To investigate reasons for T-cell dysfunction, we analyzed T-cell expression of the cytolytic protease granzyme A and of CD3ζ, the signaling component of the T-cell receptor complex. An increased proportion of CD4 and CD8 T cells from HIV-infected donors contain granzyme A, consistent with the known increased frequency of activated T cells. In 28 HIV-infected donors with mild to advanced immunodeficiency, a substantial fraction of circulating T cells downmodulated CD3ζ (fraction of T cells expressing CD3ζ, 0.74 ± 0.16 v 1.01 ± 0.07 in healthy donors; P < .0000005). CD3ζ expression is downregulated more severely in CD8 than CD4 T cells, decreases early in infection, and correlates with declining CD4 counts and disease stage. CD3ζ expression increases over 6 to 16 hours of culture in an interleukin-2–dependent manner, coincident with restoration of viral-specific cytotoxicity. Impaired T-cell receptor signaling may help explain why HIV-specific cytotoxic T lymphocytes fail to control HIV replication.

Nephritogenic T cells use granzyme C as a cytotoxic mediator

Cytoplasmic granules of cytotoxic T lymphocytes contain several proteins that may be involved in cell-mediated cytotoxicity. We have previously described nephritogenic T cell clones that are cytotoxic to cultured renal proximal tubular epithelial cells (MCT). One of these clones, M52.34.1, expresses perforin, a cytotoxic mediator. We investigated the expression of other granule-associated proteases of M52.34.1. Granzymes A and B have been extensively studied in T cell-mediated cytotoxicity, and associated with tissue destruction in models of transplantation. However, the activity of other granzymes has not been as extensively investigated. We focused our studies on granzyme C. Northern blots showed very high levels of granzymes B and C mRNA expression in M52.34.1 cells 3 days following T cell activation. There was no expression of granzyme A mRNA. An antisense oligonucleotide made from the 5'-upstream region of the murine granzyme C exon 1 inhibited granzyme C mRNA expression in M52.34.1 when added at a concentration of 50 microM to the culture medium for 2 days. There was no inhibition of granzyme C mRNA expression with the sense oligonucleotide. The granzyme C antisense oligonucleotide inhibited M52.34.1 cytotoxicity to MCT at effector:target ratios of 20:1 and 40:1. M52.34.1 cells mediate inflammatory interstitial nephritis following adoptive transfer. If T cells were resuspended in 200 microM of the antisense oligonucleotide prior to subcapsular transfer, the recipient kidneys showed markedly diminished tubular cell destruction, suggesting that granzyme C can also be an important mediator of cytotoxicity in vivo.

Recombinant human granzyme A binds to two putative HLA-associated proteins and cleaves one of them

The release of cytotoxic granule contents by cytotoxic T lymphocytes triggers apoptotic target cell death. Cytotoxic granules contain a pore-forming protein, perforin, and a group of serine proteases called granzymes. We expressed human granzyme A in bacteria as a proenzyme capable of in vitro activation by enterokinase. The recombinant activated enzyme has catalytic activity against substrates with Arg, preferably, or Lys at the P1 position, comparable to trypsin. An enzymatically inactive recombinant granzyme A, with the active site Ser mutated to Ala, was produced and used with affinity chromatography to identify potential substrates. Two granzyme A-binding cytoplasmic proteins of molecular mass 33 and 44 kDa were isolated and identified by tryptic fragment sequencing as PHAP I and II, ubiquitous putative HLA-associated proteins, previously coisolated by binding to an HLA class II peptide. PHAP II forms an SDS-stable complex with recombinant mutant granzyme A and coprecipitates with it from cytoplasmic extracts. PHAP II, either purified or in cell lysates, is cleaved by the recombinant enzyme at nanomolar concentrations to a 25-kDa fragment. PHAP II begins to be degraded within minutes of initiation of cytotoxic T lymphocyte attack. PHAP I and II are candidate participants in the granzyme A pathway of cell-mediated cytotoxicity.

Residual cytotoxicity and granzyme K expression in granzyme A-deficient cytotoxic lymphocytes

Cytotoxic lymphocytes contain granules that have the ability to induce apoptosis in susceptible target cells. The granule contents include perforin, a pore-forming molecule, and several granzymes, including A and B, which are the most abundant serine proteases in these granules. Granzyme B-deficient cytotoxic T lymphocytes (CTL) have a severe defect in their ability to rapidly induce apoptosis in their targets, but have an intact late cytotoxicity pathway that is in part perforin-dependent. In this report, we have created mice that are deficient for granzyme A and characterized their phenotype. These mice have normal growth and development and normal lymphocyte development, activation, and proliferation. Granzyme A-deficient CTL have a small but reproducible defect in their ability to induce 51Cr and 125I-UdR release from susceptible allogeneic target cells. Since other granzyme A-like tryptases could potentially account for the residual cytotoxicity in granzyme A-deficient CTL, we cloned the murine granzyme K gene, which is linked to granzyme A in humans, and proved that it is also tightly linked with murine granzyme A. The murine granzyme K gene (which encodes a tryptase similar to granzyme A) is expressed at much lower levels than granzyme A in CTL and LAK cells, but its expression is unaltered in granzyme A-/- mice. The minimal cytotoxic defect in granzyme A-/- CTL could be due to the existence of an intact, functional early killing pathway (granzyme B dependent), or to the persistent expression of additional granzyme tryptases like granzyme K.

Mechanisms Responsible for Granzyme B–Independent Cytotoxicity

Using granzyme B–deficient mice obtained by gene targeting, we previously demonstrated that granzyme B is required for the rapid induction of apoptotic target cell death by cytotoxic T lymphocytes (CTLs); however, CTLs are also equipped with additional effector mechanisms. In the present study, we examined the mechanisms responsible for granzyme B–independent cytotoxicity using in vitro lytic assays with CTLs derived from mice deficient for both granzyme B and Fas ligand (FasL) (granzyme B−/− × gld/gld) or for perforin and FasL (perforin × gld/gld). Our results show that primary mixed lymphocyte reaction (MLR)-derived CTLs from granzyme B−/− × gld/gld mice induce apoptosis of allogeneic targets with less efficiency and a longer delay than CTLs deficient for granzyme B alone. The residual cytotoxicity in granzyme B−/− × gld/gld CTLs is primarily accounted for by a perforin-dependent mechanism, since perforin−/− × gld/gld CTLs have virtually no residual cytotoxic activity in our assays. Granzyme B–independent cytotoxicity is therefore partially accounted for by the Fas pathway and partially by another perforin-dependent mechanism.

Mechanism of serum-mediated endothelial injury in scleroderma: identification of a granular enzyme in scleroderma skin and sera

Circulating endothelial cell growth-inhibitory factor with a molecular weight of 40-60 kDa was described in scleroderma (SSc) sera and shown to have a proteolytic action. In view of the recent demonstration of cellular immune activation in SSc, and because of the description of novel serine proteases in the granules of activated cytolytic T cells (granzymes), we hypothesized that granzymes represent the endothelial inhibitory principal in SSc sera. Granular enzymes were isolated from IL-2-activated nonadherent normal lymphocytes, and a 60-kDa granzyme was isolated using benzamidine-affinity column and molecular sieve column. A polyclonal antiserum was generated by immunizing rabbits with the isolated granzyme. Anti-granzyme antibody abolished SSc serum-mediated EC growth inhibition. Furthermore, a circulating protein similar to isolated granzyme was identified as a 60-kDa band on Western blots of benzamidine column-purified SSc sera. Immunofluorescence studies of SSc skin biopsies using anti-granzyme antibody demonstrated the presence of granzyme reactivity, while healthy control tissues were negative. Moreover, granzyme A gene expression was identified in SSc skin biopsies by a PCR method. The data suggest cytolytic mechanism involvement in the pathogenesis of scleroderma.

Immunosuppression by inhibition of cellular adhesion mediated by leukocyte function-associated antigen-1/intercellular adhesion molecule-1 in murine cardiac transplantation

BACKGROUND

Donor alloantigen-specific tolerance to vascularized allografts can be induced by several treatments, but the immunological mechanism(s) of these effects remain unclear. One hypothesis is that allograft unresponsiveness is correlated with a shift in the pattern of expression of the T helper 1 versus T helper 2 T-cell cytokines. We report here an extensive analysis of murine cardiac allografts, during normal first set rejection and in mice treated with anti-adhesion molecule monoclonal antibodies (mAbs), a regimen that results in prolonged unresponsiveness.

METHODS

A combination of immunohistochemical staining with a panel of mAbs, and in situ hybridization with a panel of digoxigenin-labeled riboprobes, was performed on frozen-tissue sections of cardiac allografts.

RESULTS

In several strain combinations, injection of anti-leukocyte function-associated antigen-1 and anti-intercellular adhesion molecule-1, from day 0 to day 6 after transplantation, results in significant long-term survival. Examination of tolerated cardiac allografts by in situ hybridization and immunohistochemical staining shows an altered cytokine expression pattern, although the frequency of CD3 and CD4 cells is not dramatically reduced. These allografts show a decreased frequency of interferon-gamma and interleukin (IL)-2-expressing cells and a slightly increased frequency of cells expressing IL-4 and IL-10, compared with unmodified acute rejection. A direct role of these changes in T-cell cytokine expression is demonstrated by reversal of tolerance induction and rejection of the allograft by in vivo injection of either anti-IL-10 or anti-IL-4 mAb.

CONCLUSIONS

Although there are significant differences in the frequency of different cellular subsets and patterns of cytokine gene expression, these differences are quantitatively subtle, suggesting a delicately balanced immune response that can develop a pattern of specific unresponsiveness, with relatively minor alterations in the specific T-cell response.

Secretory granule proteases in rat mast cells. Cloning of 10 different serine proteases and a carboxypeptidase A from various rat mast cell populations

Two of the major rat mast cell proteases, rat mast cell protease 1 (RMCP-1) and RMCP-2, have for many years served as important phenotypic markers for studies of various aspects of mast cell (MC) biology. However, except for these proteases only fragmentary information has been available on the structure and complexity of proteases expressed by different subpopulations of rat MCs. To address these questions, cDNA libraries were constructed from freshly isolated rat peritoneal MCs and from the rat mucosal MC line RBL-1. cDNA clones for 10 different serine proteases (RMCP-1-10), and the MC carboxypeptidase A were isolated and characterized. Six of these proteases have not been isolated previously. Based on their protease content, three separate subpopulations of MCs were identified. Connective tissue MCs (CTMCs) from the ear and peritoneum express the chymases RMCP-1 and -5, the tryptases RMCP-6, and -7 and the carboxypeptidase A. However, based on a large difference in the level of expression of RMCP-7, CTMCs of these two organs may be regarded as two separate subpopulations. RMCP-2 and the three closely related proteases of the RMCP-8 subfamily were identified as the major mucosal MC proteases in rat. In contrast to what has been reported for human MCs, no expression of cathepsin G or cathepsin G-like proteases was detected in any of the rat MC populations. To determine mRNA frequencies for the various proteases expressed by normal tissue MCs, an unamplified peritoneal MC cDNA library was screened with a panel of mono-specific cDNA probes. These results showed that peritoneal MCs are highly specialized effector cells with mRNA frequencies for the major proteases in the range of several percent of the total mRNA pool.

CTL lysis: there is a hyperbolic relation of killing rate to exocytosable granzyme A for highly cytotoxic murine cytotoxic T lymphocytes

The lysis of susceptible targets by efficient cytotoxic T lymphocytes (CTL) increases both with time and with the ratio of CTL to target. Simple methods for calculating a killing rate constant from the time dependence of killing and for calculating the relation of the killing rate constant to the concentration of exocytosable granzyme A are given. Application of these methods to the killing of target cells by the highly efficient mouse CTL AR1 is presented. AR1 needed granzyme A for efficient killing. AR1 contained sufficient exocytosable granzyme A to kill at about 80% of the rate possible at infinite exocytosable granzyme A.

An integrated genetic map of the pearl locus of mouse chromosome 13

We have used a Mus domesticus/spretus congenic animal and two interspecific backcross panels to map genetically 30 sequence-tagged sites (STSs) and 13 genes to the vicinity of the pearl locus on mouse chromosome 13. The STSs defining the mapped region are from D13Mit9 to D13Mit37, spanning 10.6 cM. Genes mapped to this region include Versican (Cspg2), GTPase activating protein (Rasa), dihydrofolate reductase (Dhfr), arylsulfatase (As-1), thrombin receptor (Cf2r), hexosaminidase b(Hexb), 3-hydroxy-3-methylglutaryl coenzyme A reductase (Hmgcr), microtubule associated protein 5/1b (Mtap5), phosphodiesterase (Pde), phosphatidylinositol 3' kinase (Pik3rl), rat integrin a1-subunit (Itga1), collagen receptor a2-subunit (Itga2), and 5-hydroxytryptamine 1a receptor (Htr1a). This high resolution genetic map of the pearl region of chromosome 13 establishes the order of multiple markers, including genes whose human homologs are located within a limited region of human chromosome 5, with respect to the phenotypic anchor marker pearl.

Transgenic mice carrying the diphtheria toxin A chain gene under the control of the granzyme A promoter: expected depletion of cytotoxic cells and unexpected depletion of CD8 T cells

We have generated transgenic mice bearing the diphtheria toxin A chain (DTA) gene under the control of granzyme A (GrA) promoter sequences (GrA-DTA). GrA is expressed in activated cytotoxic cells but not in their immediate progenitors. These GrA-DTA mice are deficient in cytotoxic functions, indicating that most cytotoxic cells express GrA in vivo. Surprisingly, one founder strain containing a multicopy GrA-DTA insert show a marked and selective deficiency in CD8+ cells in peripheral lymphoid organs. This depletion was not observed in thymus, where the distribution of CD4+ and CD8+ cells is normal. Moreover, the emigration of T cells from thymus is normal, indicating that the depletion occurs in the periphery. GrA-DTA mice should be useful as models to dissect the role of cytotoxic cells in immune responses and as recipients of normal and neoplastic hematopoietic cells. The selective depletion of CD8+ cells in one founder strain could have implications for postthymic T-cell development.

Perforin and lymphocyte-mediated cytolysis

We have discussed in the previous sections the recent progress made toward elucidating the regulatory mechanism of perforin gene transcription and the domain structure of the perforin molecule. It appears that the expression of perforin is, at least partially, controlled at the transcription level through the interaction between killer cell-specific cis- and trans- acting factors. One of such cognate pairs, NF-P motif (an EBS-homologous motif) and NF-P2 (a killer cell-specific DNA-binding protein), has been described. The regulatory mechanism of gene transcription, however, is likely to involve multiple factors which act in a coordinated fashion to bring about the most efficient expression of perforin limited strictly to activated killer lymphocytes. Through studies using synthetic peptides and recombinant perforins, it has been suggested that the N-terminal region of the perforin molecule is an important, though not the only, domain responsible for the lytic activity. Further studies are warranted to elucidate the role(s) of other potential amphiphilic structures located in the central portion of the perforin molecule in the overall pore-forming activity. The molecular basis underlying the resistance of killer lymphocytes to perforin-mediated lysis still remains an open question. Preliminary results, however, suggest that the surface protein(s) restricted to killer cells may account for their self-protection against perforin. Based on recent studies using perforin-deficient mice, the involvement of perforin in lymphocyte-mediated cytolysis both in vivo and in vitro has been confirmed. Two functional roles, a direct (lytic) and an indirect (endocytosis enhancer; conduit), both of which may contribute critically to the cell-killing event can be attributed to perforin. The fact that lymphocytes may also employ perforin-independent killing mechanism(s), e.g. Fas-dependent pathway, is beyond the scope of this review. There is, nevertheless, no doubt that these alternative cytolytic mechanisms may also play important roles in immune effector and/or regulatory responses associated with killer lymphocytes. Obviously, we are still a long way from concluding on the functional relevance of each individual cytolytic mechanism seen in different physiopathological situations. Suffice it to say, however, that a wealth of information on lymphocyte-mediated killing has already emerged through the multidisciplinary efforts conducted in our and other laboratories that promise to further dissect this complicated event in the years to come.

Cloning of cDNA for human granzyme 3

A serine protease gene was cloned from cDNA prepared from tissue isolated from human ascites. The gene codes for a protein of 264 amino acids, identified as human granzyme 3 by the N-terminal amino acid sequence. Granzyme 3 has the expected features of the chymotrypsin family of serine proteases, and is closely related to other human granzymes (40-45% identity). However, the closest granzyme 3 homologue is the recently characterized rat tryptase, RNK-Tryp-2 (75% identity). From Northern blots, granzyme 3 appears to be highly expressed in peripheral blood leukocytes, spleen, thymus, and lung tissues.

Localization and identification of granzymes A and B-expressing cells in normal human lymphoid tissue and peripheral blood

Cytoplasmic granules from activated natural killer (NK) and cytotoxic T lymphocytes (CTL) contain a pore-forming protein, perforin, and several homologous serine proteinases called granzymes. Expression of these proteins correlates with the cytolytic potential of cytotoxic lymphocytes. Using a panel of MoAbs specific for human granzyme A and B, respectively, expression of these proteinases in non-pathological lymphoid tissue and peripheral blood lymphocyte (PBL) subpopulations was investigated. Using immunohistochemistry and double stainings, the phenotype of granzyme-expressing cells in lymphoid tissue was investigated. Granzyme-positive cells were detected in all lymphoid tissues tested. No large differences in the number and distribution between granzyme A- and granzyme B-positive cells were observed. The highest number of positive cells was located in the red pulp of the spleen. Significant numbers were detected in tonsil, lymph nodes, liver and thymus. Low numbers were present in the lamina propria of non-inflamed stomach, small intestine and colon. Phenotypic analysis and cell sorting showed that most of the granzyme-positive cells in lymphoid tissue and PBL consisted of CD3-CD16+CD56+ lymphocytes. Hardly any granzyme-positive CD3+CD8+ CTL were present in peripheral blood. The synthesis of granzyme A as well as B by both CD3+CD16+CD56+ and CD3+CD8+ cells in peripheral blood was increased upon IL-2 stimulation. These results indicate that in normal lymphoid tissue the predominant cytolytic cell population is formed by the NK cells, and activated CTL are rare.

Execution and suicide: cytotoxic lymphocytes enforce Draconian laws through separate molecular pathways

With the ability to analyze cytotoxicity in animals deficient in effector molecules, the debate over the biological significance of individual effector pathways is finally being settled. For CD8+ cytotoxic T lymphocytes, the two primary cytotoxic pathways are mediated by the Fas ligand and perforin. The dichotomy between the two killing pathways is mirrored in the dichotomy between their biological roles: the primary function of the Fas ligand is the control of normal cell renewal by inducing programmed cell death of actively proliferating cells via the Fas pathway. This type of cell death is part of the normal endogenous homeostatic mechanism responsible for maintaining rapidly changing cell populations such as clonally expanding and contracting T cells. In contrast, the biological function of perforin and associated granule proteins is the killing and elimination of parasitized, non-compliant cells that arise as part of pathophysiological processes and may resist lysis pathways signalled to induce apoptosis. Thus, the main function of perforin and granzymes is the maintenance of immune surveillance against both exogenous and endogenous hazards.

Transcription of granzyme A and B genes is differentially regulated during lymphoid ontogeny

During development, thymocytes express a number of genes typical for activated peripheral T lymphocytes, including granzymes. We have now analyzed by reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry, and cytochemistry fetal liver cells and thymocytes at various developmental stages for the expression of granzyme A-G genes. At days 13-17 of gestation, only granzyme B but none of the other granzymes is expressed in fetal liver. In the most immature, Pgp-1+IL2R alpha-, thymocyte subpopulation mRNAs for granzymes A-C but not for granzymes D-G are detectable. Upon further differentiation via Pgp-1-IL-2R alpha + into more mature Pgp-1-IL-2R alpha- thymocytes the level of expression of granzymes A, B, and C gradually declines reaching its lowest level at the CD4+ 8+ double positive stage. In fetal thymic lobes depleted of lymphoid cells by treatment with deoxyguanosine, no transcripts for granzymes A, B, and C were found indicating that the PCR signals are derived exclusively from early precursor T/natural killer (NK) lineage cells rather than from residual stromal elements. In mature CD4+CD8- and CD4-CD8+ thymocytes, granzyme B mRNA is found at similar levels in both subsets whereas granzyme A mRNA is expressed selectively in the CD4-CD8+ subset. Enzymatic activity of granzyme A was only seen in a fraction of CD4-CD8+ thymocytes negative for heat stable antigen (HSA) but not in the more immature HSA+ fraction of CD4-CD8+ thymocytes. The data suggest that (a) granzyme B is a pro-thymocyte marker for all T/NK lineage cells; (b) granzyme A transcripts are associated with thymocytes with the potential to develop into the CD8+ lineage; and (c) granzyme A enzymatic activity is only expressed in the most mature CD4-CD8+ stage, suggesting that granzyme proteins are not involved in early stages of thymocyte development.

Serine proteinases of mast cell and leukocyte granules. A league of their own

Serine proteinases are hydrolases that use serine's side chain hydroxyl group to attack and cleave internal peptide bonds in peptides and proteins. They reside in all mammalian tissues, including the lung and airway. As a group, they vary tremendously in form and target specificity and have a vast repertoire of functions, many of which are critical for life. A subset of these proteinases is expressed primarily in the cytosolic granules of leukocytes from bone marrow, including mast cells. Examples are elastase-related proteinases and cathepsin G of monocytes and neutrophils, the many "granzymes" of cytotoxic T lymphocytes and natural killer (NK) cells, and the tryptases and chymases of mast cells. The pace of discovery and characterization of these granule-associated serine proteinases, fueled by technical advances in molecular biology, has accelerated rapidly in the past few years. Progress has been made in assigning possible functions to individual proteinases. However, the burgeoning numbers of these enzymes; their cell, tissue and species-dependent differences in expression; and their variety of action in vitro (despite, in many cases, shared modes of activation and recent divergence in protein evolution) have vexed and challenged those of us who are anxious to establish their roles in mammalian biology. Certainly, much remains to be discovered and clarified. The purpose of this overview is to capture the state of the art in this field, stressing the similarities as well as the differences among individual granule-associated proteinases and focusing particularly on those enzymes likely to be important in the human lung and airways.