A novel serine esterase expressed by cytotoxic T lymphocytes

Cytotoxic lymphocyte gene expression in peripheral blood leukocytes correlates with rejecting renal allografts

BACKGROUND

We have shown previously that heightened expression of the cytotoxic lymphocyte (CL) effector genes perforin (P), granzyme B (GB), and Fas ligand (FasL), is closely correlated with acute allograft rejection, particularly when two or more target genes are up-regulated.

METHODS

We used quantitative reverse transcription-polymerase chain reaction to analyze CL gene expression from peripheral blood leukocytes (PBLs) and renal allograft biopsies in 31 paired samples of PBLs and renal tissue from 25 renal allograft recipients. Our aims were (1) to determine whether the expression of CL gene expression in PBLs correlates with expression of these genes in renal allograft biopsy tissue and (2) to determine whether CL gene expression in PBLs correlates with the histological diagnosis.

RESULTS

Coordinate gene expression in PBLs and acutely rejecting allografts was found in 9/11 (82%) for P, 07/11 (64%) for GB, and 10/11 (91%) for FasL. Coordinate absence was found in 15/20 (75%) for P, 17/20 (85%) for GB, and 16/20 (80%) for FasL in nonrejecting allografts. Furthermore, up-regulation of any two genes in PBLs correlated with pathological diagnosis of rejection with excellent positive (100%) and negative (95%) predictive values.

CONCLUSION

Coordinate CL gene expression in PBLs and the allograft is usually detected. CL gene expression in PBLs is closely associated with a pathologic diagnosis of rejection. CL gene expression in PBLs may serve as a noninvasive method of monitoring for renal allograft rejection.

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.

Extracellular Granzymes A and B in Humans: Detection of Native Species During CTL Responses In Vitro and In Vivo

Activated CTLs and NK cells induce apoptosis via multiple mechanisms, including that termed granule exocytosis. The latter pathway consists of vectorial secretion of perforin and a family of granule-associated serine proteases (granzymes) to the target cell. To establish whether granzymes are released extracellularly during cytolytic reactions in vivo, ELISAs that measure the native enzymes were developed and were found to specifically detect granzyme A (GrA) and granzyme B (GrB) at picogram concentrations. Low levels of GrA and GrB were present in plasma of healthy individuals (GrA, 33.5 pg/ml (median); GrB, 11.5 pg/ml (median)), whereas significantly higher levels were present in patients with ongoing CTL response, i.e., patients suffering from infections by EBV or HIV type 1. Markedly elevated levels were also noted in synovial fluid of patients with active rheumatoid arthritis. The measurement of soluble granzymes should be useful to assess clinical disorders associated with activated CTL and NK cells. Furthermore, these results suggest that granzymes mediate biologic effects beyond their described role in apoptotic cell death.

Beta-chemokines are released from HIV-1-specific cytolytic T-cell granules complexed to proteoglycans

CD8+ lymphocytes are believed to be important in host defence against the human immunodeficiency virus (HIV)-1, inhibiting HIV-1 replication through both cytolytic and non-cytolytic pathways. The cytolytic pathway involves calcium-dependent exocytosis of perforin and granzyme proteases, as well as Fas-mediated programmed cell death, whereas the noncytolytic pathway involves the release of chemokines that prevent viral entry. Using granzyme A as a marker of cytolytic granule proteins, and macrophage inflammatory protein (MIP)-1alpha and RANTES as markers of HIV-1 inhibitory chemokines, we show that these two very different mediators of viral inhibition are both localized in the cytolytic granules of HIV-1-specific CD8+ cytotoxic T lymphocytes (CTL). Following antigen-specific activation, these mediators are secreted together, facilitating both lysis of virion-producing cells and the inhibition of free virus. In addition, RANTES, MIP-1alpha and MIP-1beta are secreted by CTL as a macromolecular complex containing sulphated proteoglycans. This association appears to have a functional significance, because heparan sulphate facilitates RANTES inhibition of HIV-1 infection of monocytes.

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.

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.

Cytotoxic T-lymphocyte interaction with fibronectin and vitronectin: activated adhesion and cosignalling

Stimulation of cloned cytotoxic T lymphocytes (CTL) with anti-T-cell receptor (TCR) monoclonal antibody (mAb) in solution resulted in rapid and sustained activation of adhesion to immobilized fibronectin (FN) but did not initiate degranulation. Addition of a second antibody (Ab) to further cross-link the TCR substantially increased the level of adhesion and also activated degranulation, as measured by release of serine esterase, in the presence of immobilized FN but not in its absence. Thus, binding to FN can provide a costimulatory signal to activate degranulation. TCR cross-linking also activated CD8-dependent adhesion to class I, and CD8 provided a costimulatory signal upon binding to class I. However, the requirements for activating adhesion and generating the costimulatory signal differed significantly for FN versus class I ligand, suggesting that these two receptor-ligand systems do not share a common mechanism of action. Co-immobilizing FN and alloantigen resulted in increased serine esterase release in comparison with that stimulated by antigen alone, and required the FN and class I be on the same surface. Peptide and antibody blocking demonstrated that CTL binding to FN, and to vitronectin (VN), was mediated by the alpha V beta 3 vitronectin receptor (VNR). Thus, VNR is activated by a signal from the TCR to mediate adhesion to FN or VN, and delivers a costimulatory signal for degranulation via a different mechanism than costimulation by CD8 binding to class I.

Stimulation of tumor-specific immunity using tumor cell plasma membrane antigen

Plasma membranes isolated from tumor cells retain biologically active class I MHC proteins on their surfaces. CD8+ T-cell activation by membrane antigen is much more effective when the small membrane vesicles (<1-microm diameter) are displayed on a surface with dimensions approaching those of a cell (5-microm diameter). Previous work had shown that tumor membrane antigen incorporated onto silica microspheres could augment tumor-specific CTL responses in vivo and significantly reduce syngeneic tumor growth. Antigen on cell-sized solid supports has been termed large multivalent immunogen (LMI). Methods are described for preparing LMI using either silica or latex microspheres. LMI made using either are active in vivo in reducing tumor growth, suggesting that the nature of the support is not critical as long as it is of the appropriate dimensions and has a surface that allows adsorption of the membrane vesicles. Latex microspheres provide some advantages over the previously described silica microspheres with respect to handling and characterization. The effects of LMI on in vivo CTL activation and tumor growth suggest that this approach may have potential for application to clinical immunotherapy of cancers.

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.

The cell-mediated cytotoxic response to influenza vaccination using an assay for granzyme B activity

The measurement of cytotoxic T lymphocyte (CTL) activity through 51Cr assays is a very labour intensive method for studying cytotoxicity in human CTL due to the necessary preparation of autologous targets for the assay. An assay for granzyme B, one of a family of serine proteinases implicated in the 'lethal hit' that leads to target cell lysis, is an alternative simple measure of CTL activation. We measured granzyme B activity using its both preferred and unique substrate tert-butyloxycarbonyl-Ala-Ala-Asp-thiobenzyl ester (BAADT) in peripheral blood mononuclear cells (PBMC) obtained from influenza vaccinated subjects, and stimulated with live virus. We found that granzyme B activity increases in parallel and correlates with cytolytic activity as measured by 51Cr release assays in these virus-stimulated PBMC cultures. The assay was then used to measure the cell-mediated cytotoxic response to influenza vaccination in ten healthy elderly subjects. Peak granzyme B activity (day 6) was measured in lysates of PBMC stimulated with influenza virus, obtained from study participants before and after vaccination. We found a significant increase in granzyme B activity from pre-vaccination levels to 4 weeks post vaccination (pre=2.77 U/mg protein, post=7.23 U/mg protein, p=0.002) and a subsequent decline in the activity measured at 12 weeks post vaccination (4.34 U/mg protein, p=0.0007). Due to its substrate specificity which is unique within the family of serine proteases, this assay is highly specific for granzyme B. The assay also avoids the potential hazard of radioactivity (51Cr) in the clinical laboratory and the need for a gamma counter. The assay of granzyme B activity, therefore, provides a simple, specific and responsive method for measuring changes in cell-mediated cytotoxic activity resulting from influenza vaccination.

Rapid killing of murine lymph node T blasts by intestinal intraepithelial lymphocytes in vitro

We examined the effect of murine intestinal intraepithelial lymphocytes (IEL) on the proliferation of murine lymph node T cells (LN-T) in vitro. An IEL fraction prevented the proliferation of LN-T stimulated with antigen and X-irradiated spleen cells, or with anti-CD3 monoclonal antibodies (mAb). Concanavalin A-activated LN-T were less sensitive. Such an inhibitory activity was recovered from a CD8-depleted population by panning of bulk IEL using anti-CD8 alpha mAb. This population of BALB/c IEL showed less granzyme A activity, and its surface markers were positive for CD8 (4%), CD3 (80-90%), CD4 (2-6%), alpha-beta TcR (45-70%), and gamma-delta TcR (4-9%). Asialo-GM1 and Thy1.2 were variably expressed, but interleukin-2 (IL-2) receptor-alpha and Fc gamma receptor were not. By contrast, no cytotoxicity against YAC-1 was detected in a CD8-depleted IEL population by a 6-h 51Cr-release assay. Although IEL from severe-combined immunodeficient mice lacking CD4, CD8 and TcR, but expressing IL-2 receptor, showed cytotoxicity against YAC-1, their inhibitory activity against LN-T was almost the same as that by IEL from BALB/c mice. When LN-T blasts (greater than 75% CD4+) activated with anti-CD3 were treated with CD8-depleted IEL, intact cellular DNA of the T blasts disappeared within 1 h with increased amounts of small-sized DNA. These results suggest that CD8- IEL directly and nonspecifically kill lymph node CD4+ T blasts and possibly down-regulate TcR-mediated proliferation of peripheral T cells in the gut epithelium.

Activity of granzyme A, a serine protease in the killing granules of cytotoxic T lymphocytes, is reduced in cells from HIV-infected hemophiliacs

Cytotoxic CD8+ lymphocytes (CTLs) kill virally infected target cells by releasing cytotoxic granules. The primary objective of this study was to determine whether the activity of granzyme A, a serine protease in the killing granules of CTLs is altered in HIV-infected hemophiliacs. A sensitive colorimetric assay that measures cleavage of a synthetic substrate, N alpha-benzyloxycarbonyl-L-lysine thiobenzyl ester (BLT), was used to quantitate granzyme A activity. Granzyme A activities from hemophiliacs were normalized to to granzyme A activities of healthy donors run concurrently. Granzyme A activity in CD8+ T cells from HIV-seropositive hemophiliacs was significantly lower than granzyme A activity in cells from HIV-seronegative hemophiliacs (0.48 units +/- 0.086/CD8+ T cell and 1.573 +/- 0.434 units/CD8+ T cell, respectively; p < 0.005). These results indicate that cytotoxic cells in HIV-infected hemophiliacs have reduced granzyme A activity, which may result in a defect in CTL-mediated cell killing in these patients.

Apoptosis--molecular mechanisms and biomedical implications

Apoptosis is a distinct form of cell death of importance in tissue development and homeostasis and in several diseases. This review summarizes current knowledge about the regulation and molecular mechanisms of apoptosis and discusses the potential role of disregulated apoptosis in several major diseases. Finally, we speculate that modulation of apoptosis may be a target in future drug therapy.

Keratinocyte conditioned medium stimulates type IV collagenase synthesis in cultured human keratinocytes and fibroblasts

We have previously shown that conditioned medium from cultured human keratinocytes stimulates proliferation of a variety of cell types involved in wound healing, as well as re-epithelialization of wounds in human skin in vitro. We now present evidence for an autocrine/paracrine control of the synthesis of type IV collagenases in human keratinocytes and fibroblasts. During wound healing, keratinocytes migrate over the wound bed, an activity coupled with lysis of basement membranes, and hence requiring the presence of collagenases. Collagenases are also needed for the production and remodelling of the granulation tissue. In order to study the autocrine/paracrine control of collagenase production in keratinocytes and fibroblasts, we stimulated these cells in culture with conditioned medium from cultured keratinocytes. Protease synthesis was determined by affinity labelling with 3H-diisopropylfluorophosphoridate (DFP) and by zymography. Keratinocyte-conditioned medium was found to increase the expression of 72 and 92 kDa type IV collagenase in human keratinocytes, and the 72 kDa collagenase in human fibroblasts, indicating that an autocrine/paracrine control mechanism is involved in collagenase production in these cell types during wound healing. This increased expression of collagenases could be partly responsible for the stimulated healing seen in wounds treated with sheets of cultured keratinocytes.

Molecular interactions in the activation of effector and precursor cytotoxic T lymphocytes

Cell-cell interactions are influenced by parameters that cannot readily be studied using either intact cells or soluble molecules. Replacing one of the pair of interacting cells with an artificial cell surface construct allows novel insights to be gained into some of these parameters. Application of this approach to the study of CTL has helped to clarify the contrasting roles of some of the various receptors that are involved in recognition, adhesion and activation. In addition, it has revealed features of these receptor ligand interactions that help to explain how CTL are able to carry out effective immune surveillance and elimination of virus-infected or tumor cells. Although not discussed in this review, artificial cell surface constructs have also been effectively employed to study the interaction of TH cells with class II bearing surfaces. Class I protein and peptide antigen can be sufficient to mediate adhesion and activate CTL effector function through the TCR and CD8. In addition, interactions of other co-receptors with their ligands can act along with TCR and CD8 in a cascade of activated adhesion and co-stimulatory signal generation to allow adhesion and response when antigen and/or class I surface densities are too low to be sufficient by themselves to initiate response. The relative contributions of the various receptor/ligand interactions to a given CTL/target encounter will depend upon the affinity of the TCR for antigen and on the densities and types of ligands, including antigen, displayed on the target cell surface. It appears that the CTL has the ability to accomplish its task in a variety of ways, providing it with considerable flexibility in recognizing and eliminating antigen-bearing target cells. Thus, downregulation of any one particular ligand on a virus-infected or tumor cell does not allow escape from CTL surveillance provided that at least a low level of class I antigen remains present. The CTL is able to employ several co-receptors specific for ligands common to many cell types without being diverted from effective immune surveillance, since these receptors only become activated to mediate high-avidity adhesion when antigen is detected by the TCR. Cloned effector CTL are most amenable to studies of the kind reviewed here, since large numbers of homogenous cells can be obtained, antigen-specific adhesion can be readily measured and response is rapid and easily quantitated.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition of cytotoxic T-lymphocyte-triggered apoptosis by target cell surface-coupled aprotinin

A variety of recent investigations have implicated granzymes A and/or B in the target cell nuclear injury which accompanies cytotoxic T-lymphocyte-mediated cytolysis. Since soluble antiproteases have had limited efficacy in inhibiting CTL-mediated lysis, we developed a method to couple aprotinin, a peptide inhibitor of serine proteases, to the surface of target cells. Aprotinin modified by N-succinimidyl 3-(2-pyridyldithio)propionate retained trypsin-inhibitory activity, and target cells modified with aprotinin had demonstrable cell surface trypsin-inhibitory activity. Flow cytometry demonstrated that aprotinin was detectable on the target cell surface but underwent modulation at a rather rapid rate. When radiolabeled, aprotinin-coupled target cells were studied in 1-2 hr CTL assays, 51Cr release was little affected, but 125IUdR release was reduced up to 75% compared to controls. Corresponding apoptosis analysed by agarose gel electrophoresis and direct cytologic visualization was similarly reduced. Thus, aprotinin bound to the surface of target cells selectively protected target cells against CTL-mediated nuclear injury, and may serve as a model for the development of novel inhibitors of CTL-mediated lysis.

Ligand western blotting for specific detection of active forms of proteases

We developed a non-radioactive method of ligand western blotting for specific detection of active forms of serine proteases. The method consists of three steps: (i) separation of proteins by electrophoresis in sodium dodecyl sulfate-polyacrylamide gel, followed by blotting of proteins to nitrocellulose membrane; (ii) binding of a specific ligand, such as soybean trypsin inhibitor labeled with biotin, to protease on the membrane; and (iii) detection of the protease-inhibitor complex by color reaction (or chemiluminescence) developed by streptavidin-conjugated peroxidase (or alkaline phosphatase). By using this method, plasmin and trypsin (serine proteases) were detected, but papain (thiol protease) or pepsin (acidic protease) was not. Plasmin was detectable up to less than 4 ng. Inactive precursors of serine protease, i.e. plasminogen and trypsinogen, did not exhibit visible bands until they were activated by treatment with streptokinase or trypsin, respectively. We applied this method to clinical samples, and succeeded in detecting plasminogen, after conversion to plasmin with streptokinase treatment, in as little as 5 microliters of serum or trypsin, as it was in 10 microliters of pancreatic juice.

Natural killer and lymphokine-activated killer cells require granzyme B for the rapid induction of apoptosis in susceptible target cells

Granzyme (Gzm) B-deficient mice obtained by gene targeting were used to assess the role of Gzm B in the mechanisms used by natural killer (NK) and lymphokine-activated killer (LAK) cells to destroy target cells. Gzm B-/- NK cells, LAK cells, and cytotoxic T lymphocytes (CTL) all are defective in their ability to rapidly induce DNA fragmentation/apoptosis in susceptible target cells. This defect can be partially corrected with long incubation times of effector and target cells. Moreover, Gzm B-/- NK cells (but not CTL or LAK cells) exhibit a defect in 51Cr release from susceptible target cells. This 51Cr release defect in Gzm B-deficient NK cells is also not overcome by prolonged incubation times or high effector-to-target cell ratios. We conclude that Gzm B plays a critical and nonredundant role in the rapid induction of DNA fragmentation/apoptosis by NK cells, LAK cells, and CTL. Gzm B may have an additional role in NK cells (but not in CTL or LAK cells) for mediating 51Cr release.

BLT-esterase in infectious mononucleosis

Peripheral blood lymphocytes of three patients suffering from infectious mononucleosis due to Epstein-Barr virus (EBV) infection were analysed for BLT-esterase expression in peripheral blood lymphocytes by a well established cytochemical staining method. During the acute phase of disease with presence of clinical symptoms a very high level of up to 90% BLT-esterase-expressing lymphocytes were detected. The increased percentage of lymphocytes expressing BLT-esterase coincided with the time of greatest symptoms and the peak elevation of hepatocellular enzymes. The still moderately elevated level only gradually decreased to normal during the further recovery period of 2 months during which the patients described episodes of weakness. Peripheral blood lymphocyte phenotype analysis revealed a marked CD8 lymphocytosis, a CD4/CD8 ratio of about 0.2, low number of CD19+ B cells, and a high level of DR+ CD3+ lymphocytes. Reduction of BLT esterase expression during the recovery period coincided with reduction of CD8+ DR+ lymphocytes. By a combination of BLT-esterase staining with immunocytochemical phenotype analysis, 95% of CD8+ lymphocytes were found to be BLT-esterase-positive. BLT-esterase might be involved in the immunodefence against EBV in infectious mononucleosis by inducing apoptosis in EBV-transformed B cells.

Natural killer (NK)-like cytotoxicity of murine intraepithelial lymphocytes in the small intestine (iIEL) and the effect of the serine proteases

The natural killer (NK)-like cytotoxicity of murine intraepithelial lymphocytes in the small intestine (iIEL) and the participation of serine proteases in it were investigated. We monitored the cytotoxicity of iIEL with a sensitive cytotoxic assay using laser flow cytometry. iIEL exhibited NK-like cytotoxicity on YAC-1 target cells. Benzamidine, a serine protease inhibitor, inhibited significantly both Na-CBZ-L-lysine thiobenzyl ester (BLT)-specific serine protease activity and iIEL-mediated NK-like cytotoxicity. These results suggest that BLT-specific serine proteases may participate in NK-like cytotoxicity of murine iIEL.

A novel ligand for CD44 is serglycin, a hematopoietic cell lineage-specific proteoglycan. Possible involvement in lymphoid cell adherence and activation

The lymphocyte adhesion molecule CD44 recognizes a non-hyaluronate proteoglycan, gp600, secreted by mouse T cell line CTLL2. We now demonstrate that gp600 is identical to serglycin, a member of the small proteoglycan family stored in intracellular secretory granules of lymphoid, myeloid, and some tumor cells. Purified gp600 has the ability to bind specifically to CD44, and the binding is dependent on activation of CD44. The CD44-binding elements on gp600 or serglycin are glycosaminoglycans consisting of chondroitin 4-sulfate. Serglycin is readily exocytosed, and its interaction with active form CD44 augments the CD3-dependent degranulation of CD44 positive CTL clones. We conclude that the serglycin secreted from secretory granules of hematopoietic cells is a novel ligand for CD44, and could regulate lymphoid cell adherence and activation.

Pretreatment with beta-funaltrexamine blocks morphine-mediated suppression of CTL activity in alloimmunized mice

The effect of prolonged exposure to morphine on cytotoxic T lymphocytes (CTL) and splenic natural killer (NK) activity was investigated. Daily administration of morphine (50.0 mg/kg, s.c.) to alloimmunized mice for 11 days resulted in a significant decrease (25-50%) in peritoneal and splenic CTL activity but not splenic NK activity. To identify the effector cell population mediating cytolysis, cell enrichment studies were carried out. The results of these studies indicated the CTLs are CD8+ CD4-. Chronic morphine treatment increased the percentage (25-30%) of CD3+ CD4+ and CD8+, but not Ig+ cells in the spleen relative to saline-treated controls. Pretreatment of mice with the mu-selective antagonist, beta-funaltrexamine blocked morphine-mediated suppression of splenic and peritoneal CTL activity as well as the increase in CD3+ CD4+ and CD8+ splenic lymphocytes. These results indicate the generation of CTLs in vivo is sensitive to chronic morphine exposure implicating opiates as important co-factors through modulation of cell-mediated immunity.

Synergistic roles of granzymes A and B in mediating target cell death by rat basophilic leukemia mast cell tumors also expressing cytolysin/perforin

We have studied the cytotoxic activity of rat basophilic leukemia (RBL) cells transfected with cDNAs for the cytotoxic T lymphocyte (CTL) granule components, cytolysin (perforin), granzyme A, and granzyme B. With red cell targets, cytolysin expression conferred potent hemolytic activity, which was not influenced by coexpression of granzymes. With tumor targets, RBL cells expressing cytolysin alone were weakly cytotoxic, but both cytolytic and nucleolytic activity were enhanced by coexpression of granzyme B. RBL cells expressing all three CTL granule components showed still higher cytotoxic activities, with apoptotic target death. Analysis of the cytotoxic activity of individual transfectant clones showed that cytolytic and nucleolytic activity correlated with granzyme expression but was independent of cytolysin expression within the range examined. A synergism between granzymes A and B was apparent when the triple transfectant was compared with RBL cells expressing cytolysin and one granzyme. These data implicate granzymes as the major mediators of tumor target damage by cytotoxic lymphocytes.

Markers of T-cell differentiation and maturation in C57BL/6 and BALB/c mice and in the calf: a comparative study

No significant differences were found between C57BL/6 and BALB/c mice in the levels of Thy 1.2 antigen (a T-cell marker) or the activities of the T-cell maturation-related enzymes adenosine deaminase (ADA, EC 3.5.4.4), serine-esterase (SE, EC 3.4.21), N-acetyl-beta-D-glucosaminidase (NABG, EC 3.2.1.30) and beta-glucuronidase (BG, EC 3.1.1.1), in either unfractionated lymphoid cells or T-lymphocyte-enriched fractions. ADA, SE, NABG and BG activities were much higher (P < 0.01) in the calf than in the corresponding populations in mice. However, the distributions of these activities among thymocyte subpopulations were very similar in mice and the calf. These results provide indirect evidence to suggest that the course of T-cell maturation is similar in mice and the calf.

Heterogeneity of murine adherent interleukin-2-activated killer cells. Differential effect of prostaglandin E2 and forskolin

We have studied the relationship between cytotoxic activity, size and granularity of murine interleukin-2-activated adherent killer cells issued from spleen cells cultured with high levels of IL-2. The effects of prostaglandin E2 (PGE2) and forskolin upon these cells were assessed. All adherent spleen cells obtained after 5 days of culture were large granular lymphocytes but presented a heterogeneity in size and granularity. After fractionation on a discontinuous-density Percoll gradient, four cellular subpopulations were isolated. Fluorescence-activated cell sorting analysis showed that cells of the lightest fraction (F1) were the largest, while the cells found in the heaviest fraction (F4) were much more granular than the cells collected in the two intermediate fractions (F2 and F3). The serine esterases level was higher in F4 than in unfractionated cells and diminished to about 40% in cells of fractions F2 and F3, which expressed a cytotoxic activity against YAC-1 cells higher than that in unfractionated cells or in F1 or F4, which presented the lowest cytotoxic activity. When AK cells were cultured for 48 h in the presence of either PGE2 or forskolin, which induce an intracellular increase of cAMP, we observed that PGE2 (1 microM) inhibited the cytotoxic activity, but surprisingly forskolin (2 microM) exerted a stimulating effect on the induction of cytotoxic activity. After fractionation on a discontinuous Percoll gradient we observed the same cellular distribution among PGE2 or forskolin-treated or -untreated cells, but PGE2 induced an increase of size and granularity. This effect of PGE2 was more potent on the cells collected in F4. However this variation of granularity was not associated with any variation in the serine esterase level. The cytotoxic activity of PGE2- or forskolin-treated cells did not present any significant variation relative to the control for cells collected in F2 and F3; on the other hand, forskolin-treated cells collected in F4 showed a significantly higher cytotoxicity than did the corresponding untreated or PGE2-treated cells.

Phorbol ester-induced reversible inactivation of cytotoxic T cell function: correlation with down-regulation of protein kinase C activity

When an H-2d-specific cytotoxic T lymphocytes (CTL) clone, FC1, was incubated in the presence of 10(-7) M phorbol myristate acetate (PMA) for 10-12 hr, the cytolytic activity of the CTL against H-2d target cells was abrogated, but was reversibly restored to the normal level after subsequent incubation of the cells in PMA-free medium for more than 10 hr. These effects of PMA have been reported (Russell, J.H.: J. Immunol. 133, 907-912 (1984)), but the mode of its action has not been fully investigated. Here, we analyzed the biochemical basis of the PMA-induced loss of cytolytic activity. Cycloheximide completely blocked the restoration of the PMA-suppressed cytolytic activity, suggesting that protein synthesis was required in this process. PMA-treatment did not affect the levels of CD3 and CD8 molecules expressed on the CTL, nor was the level of a CTL-specific serine esterase, BLT esterase, affected by this treatment. However, the target cell-induced release of BLT esterase from the CTL was suppressed if the cells were pretreated with PMA. PMA-treatment of the CTL led to the down-regulation of protein kinase C (PKC) activity by about 50%. On the other hand, staurosporin, an inhibitor of PKC, completely blocked the target cell lysis when added at 10(-6) M. These results suggest that the down-regulation of at least some isoform(s) of PKC is responsible for the PMA-induced loss of the cytotolytic activity of CTL.

Prothymosin alpha and factors from calf thymic cells decrease expression of Thy 1.2 antigen among small thymocytes from C57BL/6 mice

In this work we studied the effect of Prothymosin alpha (ProT alpha) and other thymic factors on the expression of Thy 1.2 antigen (a T-cell marker) and the activities of adenosine deaminase (ADA, E.C. 3.5.4.4), N-acetyl-beta-D-glucosaminidase (NABG, E.C. 3.2.1.30), beta-glucuronidase (BG, E.C. 3.1.1.1) and serine-esterase (SE, E.C. 3.4.21)., the levels of which change during the T-cell differentiation process among small thymocytes obtained from C57BL/6 mice. Incubation of small thymocytes in the presence of ProT alpha, Thymus Extracts (TE) or supernatants prepared from thymic stromal cells (TSCS) or thymocytes (TS) reduced the proportion of cells killed by anti-Thy 1.2 monoclonal antibodies but did not affect the enzymatic activities studied. This is the first evidence that ProT alpha affects Thy 1.2 expression in vitro.

A protein produced by a monocytic human cell line can induce apoptosis on tumor cells

A serum-free medium conditioned by U937, a human cell line of monocyte/macrophage origin, was found capable of inducing apoptosis on exponentially growing U937 cells themselves (autocrine suicide). The apoptosis-inducing agent is a macromolecule and possibly a protein (SKT factor), with a relative molecular mass in the range of 18-25 kDa. All human tumor cell lines examined have been induced to apoptosis with high efficiency, whereas non transformed human lymphocytes and monocytes are insensitive to the apoptosis-inducing activity; moreover, partially differentiated U937 are not killed but induced to full maturation. These observations suggest that the SKT factor could possibly be a cytokine with a specific cytotoxic tropism, that resembles in many respects the cytokine tumor necrosis factor (TNF), even though no TNF is detectable in the conditioned medium.

Cytotoxic lymphocytes require granzyme B for the rapid induction of DNA fragmentation and apoptosis in allogeneic target cells

We have generated H-2b mice with a homozygous null mutation in the granzyme (gzm) B gene. Gzm B is a neutral serine protease with Aspase activity that is found only in the granules of activated cytolytic T cells, natural killer cells, and lymphokine-activated killer cells. Gzm B-/- mice develop normally and have normal hematopoiesis and lymphopoiesis. In vitro, cytotoxic T lymphocytes (CTL) derived from gzm B-/- animals are able to induce 51Cr release from allotarget cells, but with reduced efficiency. However, gzm B-/- CTL have a profound defect in their ability to induce rapid DNA fragmentation and apoptosis in allogeneic target cells. This defect is kinetic since DNA fragmentation is partially compensated and 51Cr release is completely rescued with long incubation times. We conclude that gzm B serves a critical and nonredundant role for the rapid induction of target cell DNA fragmentation and apoptosis by alloreactive cytotoxic T lymphocytes.

5-Fluorouracil increases susceptibility of renal cell cancer cell lines to lymphokine-activated killer cells: evidence for alteration not at the level of recognition but at a post-binding stage of the lytic cycle

To investigate the usefulness of 5-Fluorouracil (5FU) for combination with immunotherapy, we examined the effect of preincubation with 5FU on the susceptibility of a renal cell cancer (RCC) cell line, ACHN, to lymphokine-activated killer (LAK) cells. A 4-h 51Cr release assay showed a remarkable increase in the susceptibility of ACHN cells to LAK cells. Dose response experiments demonstrated that 5FU at concentrations as low as 0.002 microgram/ml increased susceptibility to LAK cells. Presence of 5FU at 2 micrograms/ml but not at 0.2 microgram/ml in media blocked LAK activity induction by IL-2. Furthermore, an adhesion assay showed that preincubation with 5FU did not alter the adhesion of LAK cells to tumor cells nor the expression of intercellular adhesion molecule-1 (ICAM-1), lymphocyte function-associated antigen-3 (LFA-3) or major histocompatibility complex (MHC) class I molecules on tumor cells. Cold target competition did not show any difference between 5FU-treated and untreated competitors. These results suggest that increased susceptibility of RCC cells to LAK cells due to preincubation with 5FU might depend on changes in intrinsic lysability involving a post-binding stage of the lytic cycle.

1,25(OH)2D3 increases cytotoxicity and exocytosis in lymphokine-activated killer cells

The effect of 1,25-dihydroxyvitamin D3 on lymphokine-activated killer (LAK) cells activity was studied. Treatment of LAK cells with 1,25-dihydroxyvitamin D3 for 24 h increased their cytotoxic activity without affecting cell proliferation. This effect was dose-dependent, detectable already at 10(-11) M attaining 44 +/- 7% increase at 10(-8) M. 1,25-dihydroxyvitamin D3 increased LAK cell content of the cytotoxic granule granzyme A by 21%. Secretion of granzyme A by LAK cells was triggered by 12-O-tetradecanoylphorbol 13-acetate and the calcium ionophore A23187. 1,25-dihydroxyvitamin D3 decreased the lag preceding secretion, increased the rate constant of exocytosis and the fraction of granzyme A cell content secreted. The potentiation of exocytosis was more pronounced at suboptimal calcium ionophore concentration suggesting that 1,25-dihydroxyvitamin D3 affects a calcium-dependent process. Since exocytosis of cytotoxic granules is a pivotal event in the killing of tumor cells by LAK cells, it is plausible that the enhancement of this process underlies the stimulation of LAK cell cytotoxic activity by 1,25-dihydroxyvitamin D3.

Regulation of perforin gene expression in a T cell hybrid with inducible cytolytic activity

A mouse x rat T cell hybrid (PC60) that does not require interleukin (IL)-2 for proliferation, was used as a model to study regulation of perforin gene expression. Perforin mRNA is barely detectable in non-induced PC60 cells; however, a 30-fold induction is observed after stimulation with IL-1 alone. Peak perforin mRNA levels were reached after 10 h of induction with IL-1, and these levels were maintained for as long as the stimulus was present. IL-2 by itself has no detectable effect. However, in combination with IL-1 it shows the same induction kinetics as IL-1 alone for the first 10 h, subsequently there is synergism (100-fold induction) between IL-1 and IL-2. The induction response was mainly due to increased transcriptional rates of the perforin gene, and require newly synthesized proteins. The half-life of perforin mRNA in this system is about 5 h. In addition, we confirm the existence of two types of mouse perforin mRNA that differ in their 5' untranslated regions, and show evidence that both mRNA are translated in vivo with similar efficiencies.

Degradative activity of granzyme A on skeletal muscle proteins in vitro: a possible molecular mechanism for muscle fiber damage in polymyositis

The importance of cytotoxic T lymphocytes (CTLs) in the autoimmune inflammatory myopathies, especially polymyositis (PM), has been emphasized. We have studied the degradative activity of granzyme A, a cytotoxic molecule with trypsin-like specificity in CTL granules, on several muscle proteins in vitro. Our study reveals that granzyme A hydrolyzes dystrophin, myosin, and nebulin, but not laminin, alpha-actinin, vinculin, and connectin in vitro. Among these proteins, nebulin is more susceptible to proteolysis, followed by dystrophin, myosin heavy chain, and myosin light chains, in that order. This result implies an important role of granzyme A in CTL-mediated muscle fiber damage in PM.

Evidence that macrophages are programmed to die after activating autologous, cloned, antigen-specific, CD4+ T cells

The bone marrow produces large numbers of monocytes daily, but the mechanisms balancing production and elimination are unknown. In this report we demonstrate that macrophages (M phi) undergo apoptosis after activating autologous CD4+ cells. Since apoptosis is a genetically programmed response, these results argue that M phi death can be part of a normal immune response. This event may have relevance to monocyte/M phi homeostasis, as well as immune response regulation and host defenses to intracellular organisms.

Clone-specific T cell receptor antagonists of major histocompatibility complex class I-restricted cytotoxic T cells

A previous report showed that the proliferative response of helper T cells to class II major histocompatibility complex (MHC)-restricted antigens can be inhibited by analogues of the antigen, which act as T cell receptor (TCR) antagonists. Here we define and analyze peptide variants that antagonize various functions of class I MHC-restricted cytotoxic T lymphocyte (CTL) clones. Of 64 variants at individual TCR contact sites of the Kb-restricted octamer peptide ovalbumin257-264 (OVAp), a very high proportion (40%) antagonized lysis by three OVAp-specific CTL clones. This effect was highly clone specific, since many antagonists for one T cell clone have differential effects on another. We show that this inhibition of CTL function is not a result of T cell-T cell interaction, precluding veto-like phenomena as a mechanism for antagonism. Moreover, we present evidence for direct interaction between the TCR and antagonist-MHC complexes. In further analysis of the T cell response, we found that serine esterase release and cytokine production are susceptible to TCR antagonism similarly to lysis. Ca2+ flux, an early event in signaling, is also inhibited by antagonists but may be more resistant to the antagonist effect than downstream responses.

In vivo and in vitro primed lymphocytes. Correlation of cytochemically detected BLT-specific lymphoid serine protease with cytotoxic activity

We describe the validation of a cytochemical method to detect a cytolytic cell-specific lymphoid serine protease which can be upregulated during viral infection and allogeneic stimulation. The cytolytic cell specificity was ascertained by demonstrating a high correlation between BLT substrate-specific serine protease (SP) activity and cytotoxicity of in vivo and in vitro stimulated lymphocytes. The presence of SP in peripheral blood lymphocytes was compared with their capacity to kill K562 targets in a lectin-dependent cytotoxicity assay. The correlation coefficient was 0.92 and 0.93 at E:T ratios 10:1 and 20:1 respectively. In allogeneic mixed lymphocyte cultures an increase of SP activity in effector lymphocytes was paralleled by an augmentation of cytotoxic capacity towards stimulator target cells. SP+ granules showed intracellular polarization to the effector/target cell interface during conjugate formation. These results together with previous studies suggest that this method provides a sensitive assay which predicts the cytolytic potential present in a lymphocyte population.

Distribution of serine esterase activity in the lymphoid system of C57BL/6 mice, effect of aging on the enzymatic activity

1. The activity of serine esterase (SE) was investigated in the lymphoid system of C57BL/6 mice. SE activity increased in the lymphoid tissues with their content of mature T-lymphocytes, except that high levels were also observed in various populations of bone marrow cells. 2. The maturation of T-lymphocytes in the thymus was accompanied by an increase in their SE activity. 3. Experiments on the influence of age on SE activity showed that while thymocytes were not affected, a three-fold increase in activity occurs in spleen lymphocytes between the ages of 26 and 78 wk.

Interaction of papain-digested HLA class I molecules with human alloreactive cytotoxic T lymphocytes (CTL)

Acute immunological rejection events of transplanted allogeneic organs are strongly dependent on T cell reactivity against foreign MHC products. The recognition requirements of alloreactive cytotoxic T cells are of particular interest for finding approaches to modulating alloreactivity. The role of the allogeneic MHC molecule itself and/or an associated peptide in the interaction with the T cell receptor is still, however, unclear. Our studies have focused on the interactions of papain-digested HLA class I molecules with alloreactive CD8+ CTL. These polypeptides, consisting of the polymorphic alpha 1 and alpha 2 and the monomorphic alpha 3 domains, were used in both soluble and immobilized form to study their functional effects on anti-HLA-A2 reactive CTL. Purified polypeptides were of molecular mass 32-34 kD. HLA-A2 polypeptides (0.55 micrograms/ml) in soluble form induced half-maximal reduction of CTL cytotoxicity. These concentrations were quantitatively comparable to the effective doses of intact HLA class I molecules, which contain the hydrophobic transmembrane domain and the intracytoplasmic tail. In addition, specific activation requirements of these CTL were investigated in a serine esterase release assay. Maximal degranulation was observed after 2 h of antigen contact. Purified HLA class I molecules allospecifically activated the anti-HLA-A2 CTL to degranulate serine esterase, when immobilized on plastic microtitre plates. Thus, polypeptides containing the polymorphic alpha 1 and alpha 2 domains of human class I molecules potentially modulate the cytotoxic T cell response. This might have implications for the reduction or prevention of allograft rejection in recipients of foreign organs.

Lytic granules from cytotoxic T cells exhibit kinesin-dependent motility on microtubules in vitro

One major mechanism of cell-mediated cytolysis is the polarized secretion of lytic granules, a process which is highly dependent on microtubules. We isolated lytic granules from murine cytotoxic T cells and tested their ability to bind to and move along microtubules in vitro. In the presence of a motor-containing supernatant, the granules bound to the microtubules and moved along them at an average maximal rate of 1 microns/second. Virtually every granule could bind to microtubules, and about half translocated within a few seconds of binding. Motility required exogenous cytosolic motors, hydrolyzable nucleotides, and an intact granule membrane. Although the motor preparation used to support granule movement contains both plus- and minus-end-directed motor proteins, granule movement was strongly biased toward microtubule plus-ends. Inactivation of cytoplasmic dynein had little effect on granule binding and movement, but immuno-depletion of kinesin from the motor preparation inhibited granule binding by 50%. These results indicate that most granule movement in this assay is mediated by kinesin. The speed and direction of granule movement in vitro are sufficient to account for the release of lytic granules in the intact T cell. This model system should be valuable for studying the interactions of secretory granules with microtubules, and for identifying the regulatory factors involved.