The isolation and characterization of a family of serine protease genes expressed in activated cytotoxic T lymphocytes

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.

Immunosenescence Modulation by Vaccination

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

Identification and annotation of bovine granzyme genes reveals a novel granzyme encoded within the trypsin-like locus

Granzymes are a family of serine proteases found in the lytic granules of cytotoxic T lymphocytes and natural killer (NK) cells, which are involved in killing of susceptible target cells. Most information on granzymes and their enzymatic specificities derive from studies in humans and mice. Although granzymes shared by both species show a high level of conservation, the complement of granzyme genes differs between the species. The aim of this study was to identify granzyme genes expressed in cattle, determine their genomic locations and analyse their sequences to predict likely functional specificities. Orthologues of the five granzyme genes found in humans (A, B, H, K and M) were identified, as well a novel gene designated granzyme O, most closely related to granzyme A. An orthologue of granzyme O was found in pigs and a non-function version was detected in the human genome. Use of specific PCRs demonstrated that all of these genes, including granzyme O, are expressed in activated subsets of bovine lymphocytes, with particularly high levels in CD8 T cells. Consistent with findings in humans and mice, the granzyme-encoding genes were located on three distinct genomic loci, which correspond to different proteolytic enzymatic activities, namely trypsin-like, chymotrypsin-like and metase-like. Analysis of amino acid sequences indicated that the granzyme proteins have broadly similar enzymatic specificities to their human and murine counterparts but indicated that granzyme B has a different secondary specificity. These findings provide the basis for further work to examine their role in the cytotoxic activity of bovine CD8 T cells.

Granzyme B ELISPOT assay to measure influenza-specific cellular immunity

The immunogenicity and efficacy of influenza vaccination are markedly lower in the elderly. Granzyme B (GrzB), quantified in fresh cell lysates, has been suggested to be a marker of cytotoxic T lymphocyte (CTL) response and a predictor of influenza illness among vaccinated older individuals. We have developed an influenza-specific GrzB ELISPOT assay using cryopreserved PBMCs. This method was tested on 106 healthy older subjects (ages 50-74) at baseline (Day 0) and three additional time points post-vaccination (Day 3, Day 28, Day 75) with influenza A/H1N1-containing vaccine. No significant difference was seen in GrzB response between any of the time points, although influenza-specific GrzB response appears to be elevated at all post-vaccination time points. There was no correlation between GrzB response and hemagglutination inhibition (HAI) titers, indicating no relationship between the cytolytic activity and humoral antibody levels in this cohort. Additionally, a significant negative correlation between GrzB response and age was observed. These results reveal a reduction in influenza-specific GrzB response as one ages. In conclusion, we have developed and optimized an influenza-specific ELISPOT assay for use with frozen cells to quantify the CTL-specific serine protease GrzB, as a measure of cellular immunity after influenza vaccination.

ELISpot for measuring human immune responses to vaccines

The enzyme-linked immunosorbent spot (ELISpot) assay is one of the most commonly used methods to measure antigen-specific T cells in both mice and humans. Some of the primary reasons for the popularity of the method are that ELISpot is highly quantitative, can measure a broad range of magnitudes of response and is capable of assessing critical cellular immune-related activities such as IFN-γ secretion and granzyme B release. Furthermore, ELISpot is adaptable not only to the evaluation of a variety of T-cell functions, but also to B cells and innate immune cells. It is no wonder that ELISpot has evolved from a research tool to a clinical assay. Recent Phase I and II studies of cancer vaccines, tested in a variety of malignancies, have suggested that ELISpot may be a useful biomarker assay to predict clinical benefit after therapeutic immune modulation. This article will discuss the most common applications of ELISpot, overview the efforts that have been undertaken to standardize the assay and apply the method in the analysis of human clinical trials, and describe some important steps in the process of developing a clinical-grade ELISpot.

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

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

Granzyme A activates another way to die

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

Immunosenescence Modulation by Vaccination

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

Secretory lysosomes and their cargo in T and NK cells

Secretory lysosomes are specialized organelles that combine catabolic functions of conventional lysosomes with an inducible secretory potential. They are present in various hematopoietic cell types commonly characterized by the need for rapid mobilization and secretion of effector proteins. As an example, the cytotoxic effector function of T cells and natural killer cells strictly depends on the activation-dependent mobilization of such vesicles to the cytotoxic immunological synapse. This review focuses on some molecules that have been identified as cargo of secretory lysosomes and which play a major role in effector function of CTL and NK cells. We also briefly point to the fact that the dysregulation of formation and transport of secretory vesicles is causative for severe immunodeficiencies and autoimmunity observed in patients and also in mice that have been used as representative model systems to analyze the pathophysiological relevance of secretory vesicles in vivo.

Application of the granzyme B ELISPOT assay for monitoring cancer vaccine trials

Granzyme B (GrB) is present in the granules of cytolytic lymphocytes and is a key mediator of cell-mediated target cell death via the granule-mediated pathway. The release of GrB can be used as an indicator of a cytotoxic T lymphocyte response. Herein, we report that the GrB enzyme-linked immunospot assay (ELISPOT) can be used to measure ex vivo antigen-specific cytotoxicity of peripheral blood mononuclear cells from cancer patients vaccinated with a peptide-based cancer vaccine. We compare the reactivity of patients' peripheral blood mononuclear cells in the GrB ELISPOT with reactivity in the tetramer, interferon (IFN)-gamma ELISPOT, and Cr-release assays. Differences in immune response over all assays tested were found between patients and 4 response patterns were observed. Reactivity in the GrB ELISPOT was more closely associated with cytotoxicity in the Cr-release assay than the tetramer or IFN-gamma ELISPOT assays. Moreover, the higher affinity g209-2M peptide (used for vaccination) elicited greater GrB secretion than the native g209 peptide, although this difference was not observed with IFN-gamma secretion. Taken together with the fact that GrB is a specific mediator released by cytotoxic T lymphocytes, these results show that simultaneous use of the GrB ELISPOT assay with other immunologic assays may provide important additional immunologic insight into patient responses to cancer vaccines.

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

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

IFN-gamma decreases CTL generation by limiting IL-2 production: A feedback loop controlling effector cell production

IFN-gamma is produced by cytotoxic T lymphocytes (CTL) but can also decrease CTL generation. We used IFN-gamma-R1-deficient (GRKO) and IFN-gamma-deficient (GKO) mice to study the effects of IFN-gamma in MLC on the generation of CTL activity and CTL number, IL-2 production and cell proliferation. CTL activity was increased in MLC when GRKO responders or GKO stimulators and responders were used, compared to wild-type (WT) MLC. The number of cells displaying the CTL phenotype (CD3+, CD8+, CD25+) was also increased, accompanied by increased IL-2 production and proliferation. Combinations of WT or GRKO CD4+ T cells with WT or GRKO CD8+ T cells as responders showed that IFN-gamma mostly affects CD4+ T cells to limit CTL generation. Intracellular staining indicated that IL-2 production was largely by CD4+ T cells. Moreover, addition of IL-2 to WT responders mimicked GKO CTL generation and activity, whereas neutralizing IL-2 decreased CTL activity in GRKO and WT responders. Thus IFN-gamma reduces CTL generation in alloimmune responses largely by limiting proliferation of IL-2 producing CD4+ T cells. This creates a feedback loop in which effectors produce IFN-gamma that limits IL-2 production which in turn limits CTL generation.

Evaluating the cytotoxicity of innate immune effector cells using the GrB ELISPOT assay

Background

This study assessed the Granzyme B (GrB) ELISPOT as a viable alternative to the ⁵¹Cr-release assay for measuring cytotoxic activity of innate immune effector cells. We strategically selected the GrB ELISPOT assay because GrB is a hallmark effector molecule of cell-mediated destruction of target cells.

Methods

We optimized the GrB ELISPOT assay using the human-derived TALL-104 cytotoxic cell line as effectors against K562 target cells. Titration studies were performed to assess whether the ELISPOT assay could accurately enumerate the number of GrB-secreting effector cells. TALL-104 were treated with various secretion inhibitors and utilized in the GrB ELISPOT to determine if GrB measured in the ELISPOT was due to degranulation of effector cells. Additionally, CD107a expression on effector cells after effector-target interaction was utilized to further confirm the mechanism of GrB release by TALL-104 and lymphokine-activated killer (LAK) cells. Direct comparisons between the GrB ELISPOT, the IFN-γ ELISPOT and the standard ⁵¹Cr-release assays were made using human LAK cells.

Results

Titration studies demonstrated a strong correlation between the number of TALL-104 and LAK effector cells and the number of GrB spots per well. GrB secretion was detectable within 10 min of effector-target contact with optimal secretion observed at 3–4 h; in contrast, optimal IFN-γ secretion was not observed until 24 h. The protein secretion inhibitor, brefeldin A, did not inhibit the release of GrB but did abrogate IFN-γ production by TALL-104 cells. GrB secretion was abrogated by BAPTA-AM (1,2-bis-(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid tetra(acetoxymethyl) ester), which sequesters intracellular Ca²⁺, thereby preventing degranulation. The number of effector cells expressing the degranulation associated glycoprotein CD107a increased after interaction with target cells and correlated with the stimulated release of GrB measured in the ELISPOT assay.

Conclusions

Because of its high sensitivity and ability to estimate cytotoxic effector cell frequency, the GrB ELISPOT assay is a viable alternative to the ⁵¹Cr-release assay to measure MHC non-restricted cytotoxic activity of innate immune cells. Compared to the IFN-γ ELISPOT assay, the GrB ELISPOT may be a more direct measure of cytotoxic cell activity. Because GrB is one of the primary effector molecules in natural killer (NK) cell-mediated killing, detection and enumeration of GrB secreting effector cells can provide valuable insight with regards to innate immunological responses.

The Granzyme B ELISPOT assay: an alternative to the 51Cr-release assay for monitoring cell-mediated cytotoxicity

Background

The interferon-γ (IFN-γ) ELISPOT assay is one of the most useful techniques for immunological monitoring of cancer vaccine trials and has gained increased application as a measure of specific T cell activation. However, it does not assess cell-mediated cytotoxicity directly as IFN-γ secretion is not limited to only cytolytic cells. Granzyme B (GrB) is a key mediator of target cell death via the granule-mediated pathway. Therefore, the release of GrB by cytolytic lymphocytes upon effector-target interaction may be a more specific indicator of CTL and NK cytotoxic ability than IFN-γ secretion.

Methods

We assessed whether the GrB ELISPOT assay is a viable alternative to the ⁵¹Cr-release and IFN-γ ELISPOT assays for measuring antigen-specific CTL cytotoxicity. Direct comparisons between the three assays were made using human CTL cell lines (αEN-EBV and αJY) and an in vitro stimulated anti-Flu matrix peptide (FMP)-specific CTL.

Results

When the GrB ELISPOT was directly compared to the IFN-γ ELISPOT and ⁵¹Cr-release assays, excellent cross-correlation between all three assays was shown. However, measurable IFN-γ secretion in the ELISPOT assay was observed only after 1 hour of incubation and cytotoxicity assessed via the ⁵¹Cr-release assay after 4 hours, whereas GrB secretion was detectable within 10 min of effector-target contact with significant secretion observed after 1 h. Titration studies demonstrated a strong correlation between the number of effector cells and GrB spots per well. Irrelevant targets or antigens did not induce significant GrB secretion. Additionally, GrB secretion was abrogated when CTL cultures were depleted of CD8+ cells.

Conclusion

Our findings demonstrate that the GrB ELISPOT assay is a superior alternative to the ⁵¹Cr-release assay since it is significantly more sensitive and provides an estimation of cytotoxic effector cell frequency. Additionally, unlike the IFN-γ ELISPOT assay, the GrB ELISPOT directly measures the release of a cytotolytic protein. Detection of low frequency tumor-specific CTL and their specific effector functions can provide valuable insight with regards to immunological responses.

Circulating concentrations of soluble granzyme A and B increase during natural and experimental Plasmodium falciparum infections

Release of soluble Granzymes (sGranzymes) is considered to reflect activation of cytotoxic T lymphocytes and NK cells. sGranzymes and a number of pro-inflammatory cytokines were measured in plasma of malaria patients with natural or experimentally induced Plasmodium falciparum infections. Concentrations of sGranzyme A and B, IL-10, IL-12p70 and CRP were significantly increased in African children presenting with clinical malaria; IL-10 and CRP concentrations were significantly correlated with disease severity. In nonimmune Dutch volunteers which were experimentally infected by P. falciparum-infected mosquitoes, sGranzyme A increment started 1-2 days prior to clinical symptoms and microscopically detectable parasitaemia. This coincided with increases in IFNgamma, IL-12p40 and IL-8, while sGranzyme B and IL-10 levels increased 24-48 h later. The elevation of sGranzyme A and IFNgamma in nonimmune volunteers suggests that NK cells are activated upon release of parasites by infected liver cells and subsequently during blood stage infection; thus, NK cells are likely involved innate immune human host resistance in the early phase of a malaria infection.

Relationship of tumorigenic malignant melanomas to dermal elastin: an expression of tumor/stromal interaction that may be related to prognosis

Malignant melanomas, which produce a large number of substances active in connective tissue modulation, must contend with the dermis to grow and propagate. We studied the morphologic interactions between tumorigenic malignant melanomas and dermal elastin. Formalin-fixed and paraffin-embedded tissues of 108 tumorigenic malignant melanomas were stained for elastic tissue with the Verhoeff-van Gieson method. Various aspects of the relationship between malignant melanoma and dermal elastin were analyzed in relation to the histologic and clinical data using univariate and multivariate analyses. Tumor thickness, mitotic rate, and the presence of elastin remnants within the tumors were found to be independent negative prognostic factors, the latter with borderline significance. Tumors with more remnants of elastin were associated with higher stage of disease and lymph node and distant metastases. Tumor infiltration between the elastic fibers in the tumor depth was associated with high Clark level, greater tumor thickness, high stage of disease, and lymph node metastases. At least partial preservation of elastic fibers in the tumor depth was a relatively good prognostic factor whereas complete absence of elastin was an adverse factor. Focal or multifocal absence of elastin in the midst of the tumors or in their depth was usually associated with lymphocytic infiltrates. We suggest that tumors with remnants of elastic fibers and/or invasion between elastic fibers in their depth may be fast growing and highly invasive. The absence of elastin within tumors and at their advancing edge may be related to the elaboration of elastin-degrading substances by melanoma cells or various inflammatory cells. Our findings indicate that the relationship between malignant melanomas and dermal connective tissue components, specifically elastin, may have prognostic significance.

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

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

A serine protease inhibitor, N-alpha-tosyl-l-lysine chloromethyl ketone, prolongs rat hepatic allograft survival

BACKGROUND

Serine protease inhibitors have profound suppressive effects on cellular and humoral immune responses. We investigated the effect of a serine protease inhibitor, N-alpha-tosyl-l-lysine chloromethyl ketone (TLCK), on hepatic allograft survival in rats. Methods. Orthotopic hepatic transplantation was performed in an ACI (RT1(a))-to-LEW (RT1(1)) rat combination. TLCK was administered continuously at a dose of 4.4 mg/kg/day using an osmotic subcutaneous infusion minipump.

RESULTS

TLCK prolonged hepatic allograft survival. Histologic staging of acute rejection based on Banff criteria in TLCK-treated hepatic allografts was significantly lower than in untreated allografts. TLCK significantly reduced serum concentrations of interferon (IFN)-gamma and tumor necrosis factor (TNF) alpha in allograft recipients. TNF-alpha mRNA levels in TLCK-treated allografts were significantly lower than in untreated allografts. TLCK also decreased perforin mRNA levels in hepatic allografts. Hepatic infiltrates eluted from TLCK-treated allografts showed significantly lower cell-mediated lympholytic activity against donor Con A blast cervical lymph node cells than those from untreated allografts. In vitro, TLCK suppressed interleukin-2 production and [(3)H]thymidine incorporation into an allogeneic mixed lymphocyte reaction.

CONCLUSION

TLCK suppressed acute allograft rejection, suggesting a novel immunosuppressive strategy for therapy of acute organ rejection.

Selective expression and function of granzyme D in lymphohematopoietic stromal cells

Granzymes are a family of serine proteases exclusively detected in the granules of cytotoxic lymphocytes, and in mice at least eight granzymes, A to G and K, have been identified. Except for granzymes A and B, which activate the apoptotic pathway, little is known about the exact functions of the other granzymes. We have found that the granzyme D transcript is selectively expressed in functional hematopoietic stromal lines as well as primary stromal cells. Stromal lines supported growth of a pre-T lymphoma clone BTK at an efficiency proportional to the expression level of granzyme D, while a stromal line lacking granzyme D failed to do so. When the defective stromal line was transfected with granzyme D cDNA, it could efficiently support the growth of BTK cells. The results indicate that granzyme D expressed in the stromal cells plays an important role in stromal cell-lymphocyte interaction.

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.

Mechanisms and management of acute renal allograft rejection

We used RT-PCR for the molecular characterization of human renal graft rejection. The studies showed that intragraft display of mRNA encoding cytotoxic attack molecule granzyme B, and immunoregulatory cytokines IL-10 or IL-2 are correlates of acute rejection, and intrarenal expression of TGF-1 mRNA, of chronic rejection. The current immunosuppressive protocol involves the use of multiple drugs, each directed at a discrete site in the T-cell activation cascade and each with distinct side effects. The immunosuppressants can be classified as inhibitors of: transcription (CsA, tacrolimus); nucleotide synthesis (azathioprine, mycophenolate mofetil, and mizoribine); growth factor signal transduction (sirolimus); and differentiation (DSG). Polyclonal antibodies and monoclonal antibodies directed at cell surface proteins are quite effective as induction therapy or anti-rejection drugs.

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.

Perforin-enhancing protein, a low molecular weight protein of cytotoxic lymphocyte granules, enhances perforin lysis

Perforin is a 68 kD protein found in the granules of cytotoxic lymphocytes and is used by lymphocytes to form lethal pores in the membranes of the cells they kill. We and others have found that when perforin is purified, its lytic activity is markedly reduced. ELISAs indicated that our final recovery of perforin protein was excellent. We decided to determine if depletion of other granule proteins contributed to the loss of lytic activity. We isolated perforin to the point where lytic activity was diminished and added back granule proteins that had no lytic activity or detectable (antigenic) perforin. Perforin was isolated by Cu2+-immobilized metal affinity chromatography (IMAC) followed by phenyl-Superose hydrophobic interaction chromatography (HIC). Its lytic activity was enhanced by a low molecular weight (<15 kD) protein, perforin enhancing protein (PEPr). We have isolated PEPr by two methods, HIC and MonoQ. Nonlytic PEPr restored perforin to close to its original lytic activity. A protein similar if not identical to PEPr was also detectable as an 125I-labeled protein associated with lytic perforin. We propose that PEPr acts in conjunction with perforin to form lethal pores and suggest that PEPr may be the rat equivalent of the human cytotoxic lymphocyte protein, granulysin.

New paradigm for lymphocyte granule-mediated cytotoxicity. Target cells bind and internalize granzyme B, but an endosomolytic agent is necessary for cytosolic delivery and subsequent apoptosis

Lymphocyte granule-mediated apoptosis is postulated to entail the formation of membrane pores by perforin. Then soluble granzyme reaches the cytosol either through these pores or by reparative pinocytosis. We demonstrate here that Jurkat cells bind and internalize granzyme B via high affinity binding sites without toxic consequence. Apoptosis occurs, however, if sublytic perforin is added to targets washed free of soluble granzyme B. We suggest that granule-mediated apoptosis mimics viral strategies for cellular entry. Accordingly, co-internalization of granzyme B with adenovirus, a virus that escapes endosomes to reach the cytosol, also induced apoptosis. Poly(ADP-ribose) polymerase cleavage and processing of CPP32, ICE-LAP3, and Mch2 were detected at 30 min, while cytosolic acidification and DNA fragmentation occurred at 60 min. Annexin V binding and membrane permeabilization arose at 4 h. The concurrent activation of the Ced-3 proteases differed from the rate at which each cysteine protease is cleaved in vitro by granzyme B. Thus, granzyme B may not directly process these proteases in whole cells but rather may function by activating a more proximal enzyme. These results indicate that adenovirus-mediated delivery of granzyme B is suitable for elucidating biochemical events that accompany granule-mediated apoptosis.

Long-range disruption of gene expression by a selectable marker cassette

Recent studies have suggested that the retention of selectable marker cassettes (like PGK-Neo, in which a hybrid gene consisting of the phosphoglycerate kinase I promoter drives the neomycin phosphotransferase gene) in targeted loci can cause unexpected phenotypes in "knockout" mice due to disruption of expression of neighboring genes within a locus. We have studied targeted mutations in two multigene clusters, the granzyme B locus and the beta-like globin gene cluster. The insertion of PGK-Neo into the granzyme B gene, the most 5' gene in the granzyme B gene cluster, severely reduced the normal expression of multiple genes within the locus, even at distances greater than 100 kb from the mutation. Similarly, the insertion of a PGK-Neo cassette into the beta-globin locus control region (LCR) abrogates the expression of multiple globin genes downstream from the cassette. In contrast, a targeted mutation of the promyelocyte-specific cathepsin G gene (which lies just 3' to the granzyme genes in the same cluster) had minimal effects on upstream granzyme gene expression. Although the mechanism of these-long distance effects are unknown, the expression of PGK-Neo can be "captured" by the regulatory domain into which it is inserted. These results suggest that the PGK-Neo cassette can interact productively with locus control regions and thereby disrupt normal interactions between local and long-distance regulatory regions within a tissue-specific domain.

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.

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.

Expression of the cytotoxic T cell mediator granzyme B during liver allograft rejection

Cytotoxic T lymphocytes (CTL) constitute a major component of the alloreactive response following organ transplantation. The molecular mechanisms of CTL killing remain to be determined but multiple candidate molecules involved in CTL-mediated cytotoxicity have been identified. Granzyme B, a serine protease, participates in perforin-dependent pathways of cytotoxicity and is necessary for induction of DNA fragmentation in target cells. In this study the expression of granzyme B in liver biopsies obtained from liver allograft recipients was determined by semiquantitative reverse transcriptase polymerase chain reaction. Biopsies were classified into four groups--no evidence of rejection, preservation injury, acute rejection, or resolving rejection--according to histopathological criteria. There was a significantly higher frequency of transcripts for granzyme B in the acute rejection group (82.8%) compared to the no rejection (20.0%), resolving rejection (12.5%) and preservation injury (0%) groups. Analysis of granzyme B gene expression in sequential samples from individual patients prior to, and after, treatment for rejection revealed an inverse correlation between granzyme B mRNA and response to treatment. These findings indicate that the cytopathic mediator granzyme B may participate in CTL-mediated cytotoxicity during liver allograft rejection.

Cloning and characterization of a novel NK cell-specific serine protease gene and its functional 5'-flanking sequences

Rat natural killer cell Met-ase-1 (RNK-Met-1) is a 30,000 M(r) serine protease (granzyme) found in the cytolytic granules of CD3- large granular lymphocytes (LGL) with natural killer (NK) activity. To characterize the genomic sequences responsible for the CD3- LGL-restricted expression of this gene, we screened a rat genomic library with RNK-Met-1 cDNA, and obtained bacteriophage clones that contained the RNK-Met-1 gene. The RNK-Met-1 gene comprises 5 exons and spans approximately 5.2 kilobases (kb), exhibiting a similar structural organization to a class of CTL-serine proteases with protease catalytic residues encoded near the borders of exons 2, 3, and 5. The 5'-flanking region of the RNK-Met-1 gene contains a number of putative promoter and enhancer regulatory elements and shares several regions of homology with the 5'-flanking region of the mouse perforin gene. We have prepared nested deletions from approximately 3.3 kb of the 5'-flanking region of the RNK-Met-1 gene, and inserted these upstream of the chloramphenicol acetyltransferase (CAT) reporter gene. These 5'-flanking RNK-Met-1-CAT constructs were transiently transfected into rat LGL leukemia, T-lymphoma, and basophilic leukemia cell lines. The transcriptional activity of the RNK-Met-1 5'-flanking region was strong, restricted to the RNK-16 LGL leukemia and controlled by several positive cis-acting regions spread over at least 3.3 kb. The longest and most active 5'-flanking region (-3341 to -33) was also used to drive specific expression of beta-galactosidase in RNK-16. These data are consistent with the NK cell-specific expression of RNK-Met-1 and suggest the potential utility of this gene promoter in the development of transgene models of NK cell biology in vivo.

Demonstration of granzyme A and perforin messenger RNA in the synovium of patients with rheumatoid arthritis

OBJECTIVE

To examine the gene expression of 2 highly specific markers of cytotoxic T lymphocyte (CTL) activation, the serine protease granzyme A and the pore-forming protein perforin, in synovial tissue of patients with rheumatoid arthritis (RA), and to compare the findings with those in osteoarthritis (OA) synovial tissue.

METHODS

Snap-frozen synovial tissue specimens from 9 patients with RA and 5 patients with OA were examined. The number of CTL that expressed granzyme A or perforin messenger RNA was determined by in situ hybridization using nonradioactive riboprobes for granzyme A and perforin, and by a novel in situ reverse transcriptase technique. The signals were visualized by an immunogold-silver immunohistochemistry technique and compared with immunohistochemical labeling of T and B cells. Additional double-labeling was achieved using anti-type IV collagen, anti-macrophage (anti-CD68), anti-T lymphocyte (anti-CD45RO), anti-B lymphocyte (anti-CD20), and anti-natural killer cell (anti-CD56) antibodies in an alkaline phosphatase-anti-alkaline phosphatase assay.

RESULTS

Granzyme A and perforin messenger RNA (mRNA) was observed in CTL in synovial specimens from all of the RA patients, whereas in specimens from OA patients only a few, single cells with a positive mRNA signal for these molecules could be detected. In the RA specimens, the number of lymphocytes showing a positive mRNA signal for granzyme A or perforin varied from 10% to 50%, reflecting the recent findings of other investigators studying synovial fluid.

CONCLUSION

Our results demonstrate that gene expression of at least 2 CTL products, granzyme A and perforin, is up-regulated in the synovium of patients with RA compared with that in the synovium of patients with OA. These molecules presumably play an important role not only in lymphocyte-mediated cytotoxicity, but also in facilitating the migration of blood-borne mononuclear cells through the vascular basement membrane into the rheumatoid synovium.

Purification of a 24-kD protease from apoptotic tumor cells that activates DNA fragmentation

We report the purification of a protease from tumor cells undergoing apoptosis that is involved in activating DNA fragmentation. Initial studies revealed that two inhibitors of serine proteases, N-1-tosylamide-2-phenylethylchloromethyl ketone and carbobenzoxy-Ala-Ala-borophe (DK120), suppressed tumor necrosis factor or ultraviolet (UV) light-induced DNA fragmentation in the U937 histiocytic lymphoma as well as UV light-induced DNA fragmentation in the BT-20 breast carcinoma, HL-60 myelocytic leukemia, and 3T3 fibroblasts. The protease was purified by affinity chromatography with DK120 as ligand and showed high activity on a synthetic substrate preferred by elastase-like enzymes (Ala-Ala-Pro-Val p-nitroanilide), but was inactive on the trypsin substrate, N-alpha-benzyloxycarbonyl-L-lysine thiobenzyl ester, or the chymotrypsin substrate, Ala-Ala-Pro-Phe p-nitroanilide. The activity of the DK120-binding protease purified from U937 cells undergoing apoptosis was increased approximately 10-fold over that recovered from normal cells. Further purification to homogeneity by heparin-Sepharose affinity chromatography followed by reverse phase high-performance liquid chromatography revealed a single band of 24 kD on a silver-stained sodium dodecyl sulfate gel. In addition to protease activity, the purified enzyme induced DNA fragmentation into multiples of 180 basepairs in isolated U937 nuclei. These findings suggest the 24-kD protease is a novel enzyme that activates DNA fragmentation in U937 cells undergoing apoptosis.

Analysis of the role of bcl-2 in apoptosis

Cells undergo apoptosis in response to a wide range of stimuli, and this response may represent an ancient defence mechanism against pathogens. Bcl-2 is able to prevent apoptosis in many cases. Although blocking cell suicide is not directly oncogenic, enforced bcl-2 expression can lead to cancer by lengthening the life-span of cells, during which time secondary changes, such as activation of additional oncogenes like c-myc, can occur. Bcl-2 cannot block apoptosis of target cells by cytotoxic T lymphocytes. Thus cytotoxic T cells are able to fight viruses that carry anti-apoptosis genes that resemble bcl-2. Genes involved in the regulation of mammalian apoptosis are similar to those that mediate programmed cell death in C. elegans. By studying cell death genes in viruses and worms as well as mammals, we will learn more about this fascinating process.

Human granzyme B is essential for DNA fragmentation of susceptible target cells

We have partially characterized the granules of the human NK cell line, YT-INDY, and assessed granule-mediated lysis and DNA fragmentation of assorted targets. Biochemical studies demonstrated significant quantities of granzyme B (asp-ase) and a heretofore undescribed chymase but no tryptase (i.e., granzyme A or 3) or distinct met-ase. YT-INDY expressed mRNA for granzyme B, perforin and CCPX. The existence of perforin was confirmed by immunoblot. The granules lysed both human and murine NK-sensitive and NK-resistant targets. YT-INDY and NK3.3, two human cytotoxic cells, were also lysed. EGTA reduced lysis by only 50%, suggesting that a perforin-independent lytic pathway is associated with the granules. In addition, 4-(2-aminoethyl) benzenesulfonylfluoride hydrochloride (AEBSF), an inhibitor that selectively blocked the chymase and 3,4-dichloroisocoumarin (DCI), an inhibitor that inactivated both chymase and asp-ase activities, marginally affected lysis. By gel electrophoresis and 125I-labeled deoxyuridine release assay, only murine cells (SP2/0 and YAC-1) underwent DNA fragmentation, and cleavage was completely inhibited by DCI, whereas EGTA, AEBSF and aurintricarboxylic acid (ATA) had no effect. The results, therefore, underscore the central role of granzyme B in granule-mediated DNA fragmentation, emphasize that the protease acts via an ATA-resistant endonuclease pathway and stress that nucleolysis does not invariably accompany granule-mediated cytolysis. Finally, ATA inhibited the asp-ase activity of isolated but not granule-associated granzyme B. ATA, therefore, is not a specific endonuclease inhibitor and results obtained with ATA should be viewed cautiously.

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.

A promoter element of the human serine esterase granzyme B gene controls specific transcription in activated T cells

The human granzyme B gene encodes a serine protease expressed specifically in cytoplasmic granules of cytotoxic T lymphocytes, released upon effector-target cell interaction. Previous studies have shown that granzyme B mRNA was induced in T lymphocytes after antigenic or mitogenic stimulation. To study the regulation of human granzyme B gene expression during lymphocyte activation we analyzed its 5' flanking region using chloramphenicol acetyl transferase (CAT) reporter gene constructs. We show that a 208-bp fragment (-148 to +60) containing an NF-AT (nuclear factor of activated T cells)-binding site promotes CAT expression in phytohemagglutinin-activated T lymphocytes, in immobilized monoclonal anti-CD3 antibody-activated Jurkat T cell line while it is inactive in unstimulated PEER and Jurkat T cells lines or B Epstein-Barr virus-transformed cell lines.

A trypsin-like serine protease activity on activated human B cells and various B cell lines

We have studied the trypsin-like serine protease activity of human tonsillar B lymphocytes. The lysate of the low-density, in vivo activated B cells as well as the lysate of cells stimulated with anti-human IgM F(ab')2 show elevated trypsin-like serine protease activity compared to the resting subset as monitored by the cleavage of Tos-Gly-Pro-Arg-pNA. The cleavage is sensitive to N-tosyl-L-lysyl-chloromethyl ketone and benzamidine but not to iodoacetamide. Experiments with intact cells give similar results. The finding that the intact cells hydrolyze the substrate, while their supernatant does not, suggests that the protease activity is cell membrane associated. It is possible that C3 is a substrate of the enzyme since the activated B cells cleave C3, whereas the resting B cells do not, and also C3 inhibits the enzyme-substrate reaction. In addition to the ex vivo B cells, we studied the serine protease activity of certain well-characterized B cell lines. The results show a correlation between the phenotype and the enzyme expression of the cell lines. BL41, an Epstein-Barr virus (EBV)-negative Burkitt lymphoma line, with a resting phenotype, has low activity, while its EBV genome-carrying convertants E95-A-BL41, E95-C-BL41, EHR-A-BL41 and BL41/95 that have the phenotype of activated B cells, have high proteolytic activity. The lymphoblastoid cell line WW-1-LCL which has the phenotype of an immunoblast, has the highest serine protease activity. On the basis of the above data, we suggest that a rather tight correlation exists between the degree of activation and the appearance of serine protease(s) on the surface of human B cells.