Detection of perforin and granzyme A mRNA in infiltrating cells during infection of mice with lymphocytic choriomeningitis virus

Perforin-deficient CD8+ T cells mediate fatal lymphocytic choriomeningitis despite impaired cytokine production

Intracerebral (i.c.) infection with lymphocytic choriomeningitis virus (LCMV) is one of the most studied models for virus-induced immunopathology, and based on results from perforin-deficient mice, it is currently assumed that fatal disease directly reflects perforin-mediated cell lysis. However, recent studies have revealed additional functional defects within the effector T cells of LCMV-infected perforin-deficient mice, raising the possibility that perforin may not be directly involved in mediating lethal disease. For this reason, we decided to reevaluate the role of perforin in determining the outcome of i.c. infection with LCMV. We confirmed that the expansion of virus-specific CD8(+) T cells is unimpaired in perforin-deficient mice. However, despite the fact that the virus-specific CD8(+) effector T cells in perforin-deficient mice are broadly impaired in their effector function, these mice invariably succumb to i.c. infection with LCMV strain Armstrong, although a few days later than matched wild-type mice. Upon further investigation, we found that this delay correlates with the delayed recruitment of inflammatory cells to the central nervous system (CNS). However, CD8(+) effector T cells were not kept from the CNS by sequestering in infected extraneural organ sites such as liver or lungs. Thus, the observed dysfunctionality regarding the production of proinflammatory mediators probably results in the delayed recruitment of effector cells to the CNS, and this appears to be the main explanation for the delayed onset of fatal disease in perforin-deficient mice. However, once accumulated in the CNS, virus-specific CD8(+) T cells can induce fatal CNS pathology despite the absence of perforin-mediated lysis and reduced capacity to produce several key cytokines.

Cytotoxic T cells are preferentially activated in the duodenal epithelium from patients with florid coeliac disease

Villous atrophy and increased numbers of intraepithelial T cells in duodenal biopsies represent a hallmark of coeliac disease. In the present study, an attempt has been made to define whether cytotoxic cell subsets are activated in situ in the affected mucosa of susceptible individuals early after ingestion of a gluten-containing diet. Duodenal biopsies from 11 patients with coeliac disease who repeatedly underwent endoscopic biopsy after ingestion of individually dosed amounts of gluten were used for immunohistochemistry and in situ hybridization. To identify the cell subsets expressing perforin mRNA and protein, in situ hybridization and FACS analyses were performed on cells isolated from fresh biopsies. Compared with normal mucosa, the number of intraepithelial lymphocytes containing perforin mRNA and protein increased significantly in tissue samples showing moderate or florid coeliac disease and closely paralleled the severity of morphological alteration, whereas the frequency of perforin-expressing lamina propria lymphocytes increased only moderately. Cells isolated from florid biopsies that expressed perforin mRNA and protein were preferentially T-cell receptor (TCR) alphabeta T cells. The increase in both the absolute number and the percentage of lymphocytes expressing perforin mRNA indicates in situ activation of lymphocytes within the epithelial compartment in florid coeliac disease upon ingestion of a gluten-containing diet in patients predisposed to coeliac disease.

Ablation of CD8 and CD4 T cell responses by high viral loads

To evaluate the impact of sustained viral loads on anti-viral T cell responses we compared responses that cleared acute lymphocytic choriomeningitis virus infection with those that were elicited but could not resolve chronic infection. During acute infection, as replicating virus was cleared, CD8 T cell responses were down-regulated, and a pool of resting memory cells developed. In chronically infected hosts, the failure to control the infection was associated with pronounced and prolonged activation of virus-specific CD8 T cells. Nevertheless, there was a progressive diminution of their effector activities as their capacity to produce first IL-2, then TNF-alpha, and finally IFN-gamma was lost. Chronic lymphocytic choriomeningitis virus infection was also associated with differential contraction of certain CD8 T cell responses, resulting in altered immunodominance. However, this altered immunodominance was not due to selective expansion of T cells expressing particular TCR Vbeta segments during chronic infection. High viral loads were not only associated with the ablation of CD8 T cell responses, but also with impaired production of IL-2 by virus-specific CD4 T cells. Taken together, our data show that sustained exposure to high viral loads results in the progressive functional inactivation of virus-specific T cell responses, which may further promote virus persistence.

Perforin-independent beta-cell destruction by diabetogenic CD8(+) T lymphocytes in transgenic nonobese diabetic mice

Autoimmune diabetes in nonobese diabetic (NOD) mice results from destruction of pancreatic beta cells by T lymphocytes. It is believed that CD8(+) cytotoxic T lymphocytes (CTLs) effect the initial beta-cell insult in diabetes, but the mechanisms remain unclear. Studies of NOD.lpr mice have suggested that disease initiation is a Fas-dependent process, yet perforin-deficient NOD mice rarely develop diabetes despite expressing Fas. Here, we have investigated the role of perforin and Fas in the ability of beta cell-reactive CD8(+) T cells bearing a T-cell receptor (8.3-TCR) that is representative of TCRs used by CD8(+) CTLs propagated from the earliest insulitic lesions of NOD mice, and that targets an immunodominant peptide/H-2Kd complex on beta cells, to effect beta-cell damage in vitro and in vivo. In vitro, 8.3-CTLs killed antigenic peptide-pulsed non-beta-cell targets via both perforin and Fas, but they killed NOD beta cells via Fas exclusively. Perforin-deficient 8.3-TCR-transgenic NOD mice expressing an oligoclonal or monoclonal T-cell repertoire developed diabetes even more frequently than their perforin-competent littermates. These results demonstrate that diabetogenic CD8(+) CTLs representative of CTLs putatively involved in the initiation of autoimmune diabetes kill beta cells in a Fas-dependent and perforin-independent manner.

Cell adhesion and the immune system: a case study using earthworms

In the earthworm's immune system, cell adhesion, which occurs by putative receptors on leukocytes, is essential after recognition of self vs. non-self. Confrontation with foreign antigens is a normal event in the environment, replete with microbial pathogens that pose a threat to survival. To better understand what happens when an effector cell first recognizes a foreign target followed by its adhesion to it, isolated leukocytes, in sufficient quantities to be subjected to various analyses, have been extremely beneficial. In vitro approaches when accompanied by biochemical, immunological, and molecular technologies, have opened up new vistas concerning the immune response of earthworms and other invertebrates. The most recent discovery includes the preliminary identification of cell differentiation (CD) markers that play vital roles in recognitive and adhesive events. Certain leukocyte effectors show characteristics of natural killer (NK) cells that may act differently depending upon their source, whether autogeneic, allogeneic, xenogeneic, or expressed under normal or varying environmental conditions including exposure to xenobiotics. At the level of earthworm evolution, there is apparently a dissociation of phagocytosis from the process of killing by NK-like effectors. There are at least three future challenges. First, it is essential to determine the precise nature of the CD markers with respect to their molecular structure. Second, once their molecular and biochemical characteristics have been defined, the role of these markers in cellular and humoral mechanisms must be clarified in order to define effector cell products and resulting immune responses. Third, there is a need to differentiate between the several lytic factors that have been found in earthworms with respect to molecular structure, and biochemical and functional characterization.

Perforin and granzyme B lytic protein expression during chronic viral and autoimmune hepatitis

BACKGROUND

Cytotoxic T lymphocytes and Kupffer cells are essential components of the immune response during liver diseases. Recent studies have highlighted the role of cytotoxic T lymphocytes using Fas and its ligand in induced hepatocyte death during acute and chronic hepatitis.

METHODS

In the present work, the main purpose was to investigate perforin and granzyme B expression in liver biopsies of patients with chronic hepatitis (10 HBV, 14 HCV and 10 autoimmune hepatitis) using immunohistochemistry. The liver biopsies of two normal individuals were also studied in the same conditions.

RESULTS

Few intrahepatic T lymphocytes expressed perforin and granzyme B, while a large number of Kupffer cells were positive for both proteins in all the patients tested. The co-localization of perforin and granzyme B, and CD3 or CD68 antigens was visualized, respectively, in T cells and Kupffer cells, using confocal microscopy. In situ hybridization assays confirmed that perforin and granzyme B mRNAs were present in the liver during chronic hepatitis. The results were similar among the three groups of patients and whatever the activity of the disease. Perforin and granzyme B expression was lacking in liver samples from normal individuals.

CONCLUSIONS

These data suggest a minor role for the T cell-mediated perforin/granzyme B death pathway, and a putative role for Kuppfer cells via lytic protein release, during chronic hepatitis.

Beta-galactoside-binding protein secreted by activated T cells inhibits antigen-induced proliferation of T cells

We have used mRNA differential display PCR to search for genes induced in activated T cells and have found the LGALS1 (lectin, galactoside-binding, soluble) gene to be strongly up-regulated in effector T cells. The protein coded by the LGALS1 gene is a beta-galactoside-binding protein (betaGBP), which is released by cells as a monomeric negative growth factor but which can also associate into homodimers (galectin-1) with lectin properties. Northern blot analysis revealed that ex vivo isolated CD8+ effector T cells induced by a viral infection expressed high amounts of LGALS1 mRNA, whereas LGALS1 expression was almost absent in resting CD8+ T cells. LGALS1 expression could be induced in CD4+ and CD8+ T cells upon activation with the cognate peptide antigen and high levels of LGALS1 expression were found in concanavalin A-activated T cells but not in lipopolysaccharide-activated B cells. Gel filtration and Western blot analysis revealed that only monomeric betaGBP was released by activated CD8+ T cells and in vitro experiments further showed that recombinant betaGBP was able to inhibit antigen-induced proliferation of naive and antigen-experienced CD8+ T cells. Thus, these data indicate a role of betaGBP as an autocrine negative growth factor for CD8+ T cells.

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.

Reduced incidence and delayed onset of diabetes in perforin-deficient nonobese diabetic mice

To investigate the role of T cell-mediated, perforin-dependent cytotoxicity in autoimmune diabetes, perforin-deficient mice were backcrossed with the nonobese diabetes mouse strain. It was found that the incidence of spontaneous diabetes over a 1 yr period was reduced from 77% in perforin +/+ control to 16% in perforin-deficient mice. Also, the disease onset was markedly delayed (median onset of 39.5 versus 19 wk) in the latter. Insulitis with infiltration of CD4(+) and CD8(+) T cells occurred similarly in both groups of animals. Lower incidence and delayed disease onset were also evident in perforin-deficient mice when diabetes was induced by cyclophosphamide injection. Thus, perforin-dependent cytotoxicity is a crucial effector mechanism for beta cell elimination by cytotoxic T cells in autoimmune diabetes. However, in the absence of perforin chronic inflammation of the islets can lead to diabetogenic beta cell loss by less efficient secondary effector mechanisms.

A simple method for evaluating the rejection of grafted spleen cells by flow cytometry and tracing adoptively transferred cells by light microscopy

In this report we describe a simple method using the vital dye 5- (and 6-) carboxyfluorescein diacetate succinimidyl ester (CFSE) to follow splenic graft rejection by flow cytometry. CFSE-labelled spleen cell suspensions were injected intravenously into various recipients and blood samples were taken at different time points to follow the transferred cells. We found that the labelled cells could be readily detected by flow cytometry for up to eleven weeks. The loss of these labelled cells in various transfusion experiments with different major and minor histocompatibility differences followed the rejection kinetics previously described for skin transplants. Thus, this method offers a simple tool to test the histocompatibility of donor cells/grafts with the host in adoptive/transplantation experiments in which donor and host are not completely syngeneic. Furthermore, we developed a method to trace adoptively transferred fluorescent CFSE-labelled cells by light microscopy by converting in situ immunofluorescence staining into immunoenzyme staining.

Induction of degenerative brain lesions after adoptive transfer of brain lymphocytes from Borna disease virus-infected rats: presence of CD8+ T cells and perforin mRNA

Lymphocytes were isolated from the brains of Borna disease virus-infected donor Lewis rats at various time points after infection. Cell populations were characterized by cytofluorometry, with special emphasis on CD4+ and CD8+ cells. Testing of isolated lymphocytes revealed major histocompatibility complex class I-restricted cytotoxic activity. Reverse transcription-PCR analyses of brain homogenates of infected donors revealed the presence of CD8 mRNA after day 11 of infection and of perforin mRNA between days 13 and 25 after infection. Adoptive transfers of lymphocytes isolated from the brain at days 13 and 21 resulted in severe neurological symptoms, resembling experimental Borna disease. The onset of disease was dependent on the cell numbers transferred and was clearly related to the appearance of T cells in the brain. CD8+ T cells were found in the parenchyma, whereas CD4+ T cells were found predominantly in perivascular locations. A disseminated lymphocytic infiltration in the parenchyma was accompanied by severe morphological alterations, including significant necrosis of neurons. Furthermore, a prominent spongiform-like degeneration was observed; this increased over time and finally resulted in severe cortical brain atrophy. Lymphocytes obtained during the beginning chronic phase of experimental Borna disease in rats had no significant cytolytic capacity in vitro and were also not able to induce neurological symptoms typical of Borna disease after adoptive transfer. The data presented here show for the first time that lymphocytes isolated from the site of the inflammatory lesions, namely, the brains of diseased rats, induce the immunopathological reaction and cause Borna disease. After transfer, the pathological alterations induced in the recipients exactly reflect those observed during experimentally induced Borna disease in rats, including necrosis of neurons and glial cells and gross degeneration resulting in cortical brain atrophy. Evidence that the immunopathology of Borna disease is closely related to the presence of CD8+ T cells in the brain parenchyma is provided.

Molecular mechanisms of lymphocyte-mediated cytotoxicity and their role in immunological protection and pathogenesis in vivo

Studies with perforin-deficient mice have demonstrated that two independent mechanisms account for T cell-mediated cytotoxicity: A main pathway is mediated by the secretion of the pore-forming protein perforin by the cytotoxic T cell, whereas an alternative nonsecretory pathway relies on the interaction of the Fas ligand that is upregulated during T cell activation with the apoptosis-inducing Fas molecule on the target cell. NK cells use the former pathway exclusively. The protective role of the perforin-dependent pathway has been shown for infection with the noncytopathic lymphocytic choriomeningitis virus, for infection with Listeria monocytogenes, and for the elimination of tumor cells by T cells and NK cells. In contrast, perforin-dependent cytotoxicity is not involved in protection against the cytopathic vaccinia virus and vesicular stomatitis virus. LCMV-induced immunopathology and autoimmune diabetes have been found to require perforin-expression. A contribution of perforin-dependent cytotoxicity to the rejection of MHC class I-disparate heart grafts has also been observed. Its absence is efficiently compensated in rejection of fully allogeneic organ or skin grafts. So far, evidence for a role of Fas-dependent cytotoxicity as a T cell effector mechanism in vivo is lacking. Current data suggest that the main function of Fas may be in regulation of the immune response and apparently less at the level of an effector mechanism in host defense. Further analysis is necessary, however, to settle this point finally.

Expression of granzyme A and perforin in mouse heart transplants immunosuppressed with donor-specific transfusion and anti-CD4 monoclonal antibody

Granzyme A and perforin are produced by activated cytotoxic T lymphocytes and their expression correlates with the appearance of cytotoxicity. Using in situ hybridization and immunohistochemistry, we examined the phenotype of cellular infiltration and the appearance of granzyme A+ and perforin+ cells in a mouse cardiac transplant model where the recipients were pretreated with donor-specific transfusion, anti-CD4 monoclonal antibody, or both. While the profiles of cellular infiltration failed to correlate with graft survival, tolerized grafts, as compared with untreated allografts, showed a decreased frequency of granzyme A and perforin expression. These functional markers of cytotoxic T lymphocytes can differentiate between rejecting and indefinitely surviving grafts and may be of value in dissecting the immunological events involved in tolerance induction.

Perforin expression in peripheral blood lymphocytes in rejecting and tolerant kidney transplant recipients

Perforin (P) is a cytolytic molecule expressed in the granules of cytolytic T cells and natural killer cells. Although cytotoxic cells have been implicated in graft rejection, no prospective clinical study has been published that examines the dynamics of perforin expressing cells in peripheral blood lymphocytes of transplanted patients. The cytofluorimetric assay developed in our laboratory previously for the simultaneous detection of intracellular perforin together with cell surface molecules was used for posttransplantation monitoring of patients, for the assessment of the efficiency of immunosuppressive treatment, and for the prediction of acute kidney transplant rejection and the stability of tolerance to long lived kidney transplants. Immunosuppression for the purpose of allotransplantation causes a decline in the number of perforin-expressing cells in peripheral blood. In contrast, in patients with clinical signs of acute rejection, the total number of perforin-expressing lymphocytes was increased in comparison with nonrejecting patients. Analyzing perforin-expressing subsets, rejection crises were accompanied by a relative decrease of perforin expression in the CD4+ subpopulation while increasing in the CD8+ subset. In the CD56+ and CD16+ NK subpopulations changes in perforin expression were mixed. In nonrejecting patients the ratio of perforin expression in CD4+ cells was high compared with CD8+ cells. Intensive therapy of acute rejection episodes with high doses of corticosteroids (methylprednisolonet [Solumedrol] bolus) strongly and significantly decreased the percentage of both, the subpopulations of perforin-positive T cells and the subpopulation of CD56+P+ NK cells. The lowest level of perforin expression, including low frequencies of perforin among CD8+ and CD4+ cells, was found in the group of patients tolerating transplanted kidneys for several years. These changes in perforin protein expression in peripheral blood can be used to discriminate between immunosuppressed patients who are immunologically quiescent and those who undergo transplant rejection. Our results confirm the hypothesis that cytotoxicity mediated by perforin may be an important effector mechanism in the rejection of allografted kidneys.

The role of perforin-expression by granular metrial gland cells in pregnancy

The pregnant uterus of humans and rodents contains a population of granulated lymphoid cells, which, in the mouse, are called granular metrial gland (GMG) cells and have been described to express high levels of perforin. Since there is evidence for cytolytic activity of these cells and since perforin is a crucial effector molecule for the lytic action of cytotoxic T cells and natural killer cells, we evaluated the function of perforin in the pregnant uterus by using perforin-deficient mice. Perforin-deficient female mice were found to reproduce as efficiently as normal control females when bred either with syngeneic or allogeneic males. However, perforin-deficient mice differed from normal mice in that the frequency of GMG cells was significantly higher within maternal blood spaces and within several compartments of the feto-maternal interface. Proliferating GMG cells, identified by [3H] thymidine incorporation, were observed during more advanced stages of pregnancy when compared to normal controls. In contrast to normal mice, perforin-deficient mice did not display GMG cells attached to degenerating trophoblasts; instead perforin-deficient GMG cells were often observed in association with small maternal lymphocytes. In addition, the lack of transmission of lymphocytic choriomeningitis virus from infected pregnant perforin-deficient mice to the fetuses argued against a role of perforin expression by GMG cells in prevention of virus transmission from the mother to the fetus. Our data indicate that functional perforin is not necessary for successful pregnancies. The morphological changes in the pregnant uterus of perforin-deficient mice might, however, point to a certain, as-yet undefined function of perforin in the uterus of pregnant normal mice, which is functionally compensated in perforin-deficient mice.

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

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

Lymphocytic choriomeningitis virus infection is associated with long-standing perturbation of LFA-1 expression on CD8+ T cells

Flow cytometric analysis of splenocytes from mice infected with lymphocytic choriomeningitis virus revealed marked and long-standing up-regulation of LFA-1 expression on CD8+, but not on CD4+ T cells. Appearance of CD8+ T cells with a changed expression of adhesion molecules reflected polyclonal activation and expansion which was demonstrated not to depend on CD4+ T cells or their products. Cell sorting experiments defined virus-specific CTL to be included in this population (LFA-1hiMEL-14lo), but since about 80% of splenic CD8+ T cells have a changed phenotype, extensive bystander activation must take place; this is indicated also by the finding that CD8+LFA-1hi cells transiently express several markers of cellular activation, e.g. transferrin receptor, IL-2R alpha and beta. Analysis of cells from the cerebrospinal fluid of mice infected intracerebrally showed that virtually all T cells present belonged to the CD8+LFA-1hi subset and, correspondingly, the ligand ICAM-1 was found to be up-regulated on endothelial cells in the inflamed meninges. Preincubation of LCMV-primed donor splenocytes with anti-LFA-1 markedly inhibited the transfer of virus-specific delayed-type hypersensitivity to naive recipients. Together, these findings indicate that up-regulation of LFA-1 expression is a critical factor involved in directing activated CD8+ T cells to sites of viral infection.

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.

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

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

Expression of granzyme A and B proteins by cytotoxic lymphocytes involved in acute renal allograft rejection

Granzymes A and B are serine-proteinases stored in the granules of activated cytotoxic T-lymphocytes and natural killer (NK) cells. Expression of granzymes in tissues can be used as an activation marker for cytotoxic cells. Using mAbs specific for human granzyme A or B in immunohistochemical staining techniques we investigated expression of granzyme A and B by lymphocytes infiltrating acutely rejected renal allografts. Twelve core needle biopsies were taken from ten different patients during an episode of acute rejection. Eleven biopsies contained high numbers of granzyme A and B positive lymphocytes infiltrating tubular epithelium, and vascular and glomerular structures. In one patient infiltrating lymphocytes did not express granzyme A and only low amounts of granzyme B. No correlation was found between the number of granzyme positive cells and the severity of the rejection as classified by conventional histological criteria. In one tissue specimen from a patient with a renal allograft without signs of rejection, the number of granzyme positive cells was much lower compared to that of the transplant group. In spite of the presence of a marked inflammatory infiltrate, no granzyme positive cells were detected in renal biopsies from patients with various inflammatory, not transplant-related, renal diseases. Phenotypic analysis showed that granzymes A and B were expressed by CD56+ NK cells and CD3+ cells, representing cytotoxic T-lymphocytes. Thus, this study demonstrates that granzyme A and B protein-expressing lymphocytes infiltrate the kidney allografts during an acute cellular rejection but not in several other inflammatory renal diseases.(ABSTRACT TRUNCATED AT 250 WORDS)

Granzyme-positive cytotoxic cells are specifically increased in early rheumatoid synovial tissue

OBJECTIVE

To define the expression and the phenotype of granzyme (Gran) A and B positive cytotoxic cells in synovial tissue (ST) from patients with rheumatoid arthritis (RA) with respect to disease duration and activity.

METHODS

Using antibodies against GranA and GranB, which serve as markers of activated natural killer (NK) cells and cytotoxic T lymphocytes, ST sections from 10 patients with early RA, 10 patients with longstanding RA, and 10 patients with osteoarthritis were examined. The phenotype of Gran+ cells was determined with double-labeling techniques.

RESULTS

Gran+ cells, the majority of which were NK cells, were found in ST from patients in all groups. Several of these cells did not express the surface markers CD16, CD56, and CD57. The highest ST expression of GranB was found in patients with early RA. In RA patients, there was a positive correlation of GranB expression with serum levels of acute-phase reactants, but not with histologic scores for inflammation.

CONCLUSION

Gran+ cells are mainly NK cells, a substantial proportion of which do not express conventional NK cell surface markers. GranB expression is specifically increased in the synovial tissues of patients with RA of short duration.

Perforin expression by thyroid-infiltrating T cells in autoimmune thyroid disease

Infiltration of the thyroid gland by lymphocytes is a hall-mark of autoimmune thyroid disease; it is particularly evident in Hashimoto's thyroiditis but is also seen in most patients with Graves' disease. Infiltrating cells are comprised primarily of T lymphocytes, of which only a minority appears to be activated. Their precise pathogenic role is largely unknown. Since perforin has been a marker for functionally activated cytotoxic T cells in situ we elected to assess the presence of perforin-containing cells in thyroid-infiltrating lymphocytes and establish their phenotype. Cells were isolated from seven subtotal thyroidectomy specimens, five from patients with Graves' disease and two with Hashimoto's thyroiditis. The novel findings were as follows: CD4+ perforin-containing T cells occurred only in Hashimoto's glands, suggesting a class II-restricted component of cytotoxicity; in Graves' disease, and to a lesser extent in Hashimoto's, perforin-expressing cells were primarily T cell receptor alpha beta- CD4-CD8- (double negative); double negative perforin-containing cells in peripheral blood of normal individuals were largely gamma delta + T cells. In Hashimoto's samples, the predominant population of T cells expressing perforin was CD8+. By comparison, in studies of the synovial fluid of knee joints from patients with rheumatoid arthritis only a minor population of the perforin-containing cells was double-negative. The data suggest significant differences in cytotoxic autoimmune mechanisms between the two autoimmune thyroid diseases. Functional characterization of double-negative T cells is necessary to define their role in autoimmunity.

Cytotoxicity mediated by T cells and natural killer cells is greatly impaired in perforin-deficient mice

Perforin-deficient mice have been generated by homologous recombination to determine whether the effects of CD8+ cytolytic T cells and natural killer cells are mediated by pore formation involving perforin. These mice are viable and fertile and have normal numbers of CD8+ T cells and natural killer cells which do not lyse virus-infected or allogeneic fibroblasts or natural killer target cells in vitro. The mice fail to clear lymphocytic choriomeningitis virus and they eliminate fibrosarcoma tumour cells with reduced efficiency. Perforin is therefore a key effector molecule for T-cell- and natural killer-cell-mediated cytolysis.

Immunohistochemical analysis of perforin and granzyme A in inflammatory myopathies

Perforin (PF) and granzyme A (GA) are candidates suspected of being cytolytic proteins of the granules of cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. We analysed PF and GA in muscles from patients with inflammatory myopathies. Five cases of polymyositis (PM), two cases of inclusion body myositis (IBM), and five cases of dermatomyositis (DM) were studied immunohistochemically using anti-PF and GA antibodies raised against each synthetic peptide of human PF and mouse GA, together with a panel of monoclonal antibodies reactive for lymphocyte subsets. In PM and IBM, PF positive cells were colocalized with GA positive cells and occasionally invaded into the non-necrotic muscle fibres. The percentage of PF positive cells among the endomysial CD8 positive cell population was 9.9% (PM) and 12.5% (IBM), and the majority of the endomysial CD8 positive cells were alpha/beta T cells. In contrast, in DM, both PF and GA positive cells were very few in all cases. Only few inflammatory cells were CD16+ or CD57+ NK cells among these diseases. Our results suggest that PF and GA are secreted mainly from alpha/beta T cells, and may play a key role in muscle fibre damage in at least some PM and IBM, but not in DM.

Mycosis fungoides skin lesions contain CD8+ tumor-infiltrating lymphocytes expressing an activated, MHC-restricted cytotoxic T-lymphocyte phenotype

In prior studies, we showed that most CD8+ cells infiltrating skin lesions of CD3+CD4+ mycosis fungoides were CD3+ T-lineage tumor-infiltrating lymphocytes (TIL) whose overall phenotype was suggestive of MHC-restricted cytotoxic T lymphocytes (CTL). However, their lack of cytotoxic-associated granzyme A mRNA suggested that they might be unactivated CTL precursors. In this study, we used single- and double-label immunohistologic techniques to assess the expression of TIA-1-reactive protein and HLA-DR by these CD8+TIL. Monoclonal antibody TIA-1 recognizes a novel family of proteins expressed preferentially by cytotoxic cells, including some that lack granzyme A. HLA-DR is a marker of T-cell activation. Single-label studies of 32 cases showed that CD8+TIL and TIA-1+ cells constituted a variable minority of the total cellular infiltrate and had a similar distribution. Double-label studies of 14 cases showed that in most instances the aggregate phenotype of the majority of CD8+TIL was CD3+TIA-1+HLA-DR+CD56-CD57-. These findings suggest that many of the CD8+TIL within skin lesions of CD3+CD4+ mycosis fungoides are activated, MHC-restricted CTL.

Regulation of RAG-1 and CD69 expression in the thymus during positive and negative selection

Successful interaction of the T cell receptor (TCR) with major histocompatibility complex (MHC) molecules during thymic selection down-regulates the expression of the recombination activating genes (RAG)-1 and -2 in cortical thymocytes and thereby prevents further endogenous TCR alpha-chain gene rearrangements (Borgulya, P., Kishi, H., Uematsu, Y. and von Boehmer, H., Cell. 1992. 69: 529-537; Brändle, D., Müller, C., Rülicke, T., Hengartner, H. and Pircher, H., Proc. Natl. Acad. Sci. USA 1992. 89: 9529-9533). To address the question whether down-regulation of RAG-1 activity represents an irreversible process we have blocked TCR-MHC interactions of thymocytes with thymic stromal cells. Firstly, transgenic (Tg) mice expressing a virus-specific MHC class I (H-2Db)-restricted TCR were injected with anti-Db or anti-CD8 monoclonal antibodies and RAG-1 expression was examined by in situ hybridization on thymus sections. The results show that cortical thymocytes up-regulated RAG-1 expression within 24 h after antibody administration. Secondly, immature thymocytes from TCR Tg mice were released from the thymic microenvironment and cultured in vitro for 14 h in single-cell suspension. The amount of RAG-1 mRNA was increased sixfold in cultured cells when compared to freshly isolated thymocytes. In addition, we show that immature thymocytes from TCR transgenic mice bearing non-selective MHC molecules (H-2d) down-regulated RAG-1 expression after antigen-induced TCR engagement. Cytofluorometric analysis further revealed that surface expression of CD69 on immature thymocytes inversely correlated with RAG-1 expression during positive and negative selection processes.

Expression of cathepsin G-like and alpha 1-antichymotrypsin-like proteins in reactive astrocytes

The central nervous system (CNS) of many different species responds to diverse neurologic injuries with an activation of astrocytes. Yet, the exact function of this reactive astrocytosis is unknown. In this report, mouse astrocytes were activated in vivo by focal penetrating brain injury. Reactive astrocytes were stained with antibodies raised against the serine protease cathepsin G (cat.G), the serine protease inhibitor alpha 1-antichymotrypsin (ACT), or the astrocytic marker glial fibrillary acidic protein (GFAP). Reactive astrocytes expressing both cat.G-like and ACT-like antigens were found around cerebral wound margins between 18 h and 13 days after neural lesions. The injury-induced immunostaining was unaltered by 900 rads of total body irradiation, suggesting that the astroglial reaction was relatively independent of bone marrow-derived cells. The in vivo immunostaining was complemented with biochemical assays on cultured primary astrocytes. A synthetic peptide was used as a substrate in combination with specific inhibitors to identify a proteolytic activity within astroglial lysates and culture supernatants that closely resembles cat.G. This activity increased substantially upon stimulation of astrocytes with dibutyryl cyclic AMP and was neutralized by antibodies raised against cat.G. In a separate report, it was shown that astrocytes also contain an ACT-like inhibitory activity. The production of ACT- and cat.G-like antigens and activities by activated astrocytes should allow these cells to participate in a number of important biologic processes. Many of these processes may benefit the CNS by assisting in early wound repair. However, astroglial proteases and their inhibitors could also contribute to the pathogenesis of certain neurologic diseases.

Distribution of perforin-containing cells in normal and pregnant mice

Cytotoxic T lymphocytes (CTL) and natural killer (NK) cells elaborate a cytolytic protein named perforin or cytolysin. It was widely held that, in vivo, high quantities of perforin are not present in resting lymphocytes and are usually produced only by activated lymphocytes found under pathological conditions. Until now, only one tissue was known to synthesize abundant quantities of perforin under nonpathological conditions, the uterus during pregnancy. To investigate the possibility that perforin might also be synthesized by other tissues, several tissues besides the uterus from pregnant and normal mice were tested by immunofluorescence and immunoperoxidase for the presence of perforin. The tissues studied were the ears, brain, nasal epithelium, tongue, salivary gland, larynx, thymus, stomach, liver, spleen, small intestine, and lymph nodes; two cell populations with different sizes and levels of perforin expression were found. Large cells, displaying the NK cell phenotype and expressing high levels of perforin, were detected not only in the uterus but also in the salivary gland and lungs of pregnant mice. Small cells, expressing low levels of perforin, were detected mainly in the stomach and small intestine, and they were expressed in both pregnant and normal mice. Taken together, these results imply that perforin-containing cells exist in vivo under nonpathological conditions, and that the immune system is endowed with heretofore unknown mechanisms for stimulating the activation of NK cells in a limited number of tissues during pregnancy.

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.

Granzyme A-immunoreactive cells in synovial fluid in reactive and rheumatoid arthritis

Perforin and granzyme A co-localize in the cytotoxic granules of killer cells like cytotoxic T lymphocytes (CTL). Perforin is the cytolytic pore-forming protein, whereas the function of the homodimeric serine protease granzyme A and other members of the granzyme family is still unclear. Granzyme A-immunoreactive cells formed 8 +/- 2% of the resting peripheral blood lymphocytes of healthy individuals. In contrast, granzyme A-positive cells formed 15% of peripheral blood mononuclear cells in patients with reactive or rheumatoid arthritis. However, 29 +/- 4% (p < 0.05 compared to normal peripheral blood) and 25 +/- 4% (p < 0.05) of all lymphocytes in synovial fluid in reactive and rheumatoid arthritis, respectively, were granzyme A-positive. This suggests involvement of cell-mediated cytolytic mechanisms in the articular pathogenic mechanisms. This involvement, however, does not differentiate between reactive and rheumatoid arthritis.

Engagement of the T-cell receptor during positive selection in the thymus down-regulates RAG-1 expression

We have examined the expression of the recombination activating gene RAG-1 by in situ hybridization to thymi from mice bearing transgenes for the T-cell receptor (TCR) alpha chain, TCR beta chain, or both TCR alpha and beta chains. RAG-1 transcription was found in the thymic cortex of transgenic mice carrying a single TCR alpha- or TCR beta-chain transgene, comparable to normal mice. However, RAG-1 transcription was strikingly reduced in the thymic cortex from transgenic mice carrying both TCR alpha- and beta-chain genes and expressing major histocompatibility complex (MHC) class I (H-2b) molecules necessary for positive selection of the transgenic TCR. In contrast, thymi of transgenic mice also carrying both TCR alpha- and beta-chain genes but expressing MHC molecules (H-2d) that did not positively select the transgenic TCR displayed high levels of RAG-1 transcription. The low thymic RAG-1 expression coincided with high transgenic TCR alpha-chain surface expression and with inhibition of endogenous TCR alpha-chain rearrangement. Our findings suggest that binding of the TCR to self MHC molecules during positive selection down-regulates RAG-1 transcription in cortical thymocytes and thereby prevents further TCR alpha-chain rearrangements.

Perforin gene expression in stimulated human peripheral blood T cells studied by in situ hybridization and northern blotting analysis

In situ hybridization was used here to monitor the mRNA level of the pore-forming protein perforin in mitogen-stimulated primary peripheral blood human T cells. In situ hybridization was performed using sense and antisense ribonucleotide probes specific for this granule mediator. After IL-2 treatment, an increase in perforin mRNA could be detected by 4 h; they peaked at 12 h, and decreased after 24 h. The perforin mRNA was also induced in T cells treated with a combination of phorbol ester PMA plus lectin or OKT3 mAb. This latter induction followed slower kinetics, peaking at 48 h. For all three mitogens used, even at peak induction times less than 10% of T cells were labeled with perforin probe. Similar patterns of mRNA expression were observed for both unprimed T cells and lectin-primed T blasts. The induction response of mRNA due to IL-2 stimulation is probably mediated by the IL-2 receptor p75 chain since its mRNA was upregulated by IL-2 with a kinetics comparable to that associated with an increase of perforin mRNA. The p55 IL-2 receptor chain increased much more slowly than p75.

Expression of perforin in murine natural killer cells and cytotoxic T lymphocytes in vivo

We have previously detected perforin expression in a subpopulation of asialo GM1+ natural killer (NK) cells and CD8+ T lymphocytes in murine spleen cells by immunocytochemical staining with an anti-perforin monoclonal antibody. In the present study, more detailed analyses of perforin expression in murine cytotoxic lymphocyte subpopulations were performed. The expression of perforin in asialo GM1+ spleen cells was predominantly confined to the NK1.1+ subset, where all NK activity also resided. Perforin expression was also studied on alloreactive cytotoxic T lymphocyte (CTL) induced in vivo. The cells expressing perforin in peritoneal exudate lymphocytes predominantly resided in the CD8+ T cell subpopulation co-expressing asialo GM1 where an allospecific CTL activity also resided. Furthermore, the percentage of perforin-positive cells in this population was greatly reduced after stimulation with anti-CD3 or anti-T cell receptors antibodies, which induce serine esterase release from the cytoplasmic granules. These findings highly suggest that perforin is involved in in vivo NK cell- and CTL-mediated cytolysis.

Perforin and granzyme A expression identifying cytolytic lymphocytes in rheumatoid arthritis

Lymphocytes from the synovial fluid of patients with rheumatoid arthritis were examined for the expression of granzyme A and perforin. Previous studies have demonstrated that the expression of these proteins, which are implicated as mediators of cytotoxicity, can be used to identify putative cytolytic lymphocytes in vivo. Twenty-two synovial fluid samples were analyzed by in situ hybridization and immunohistochemistry. In six patients receiving low doses of immunosuppressant, a population of granzyme A- and perforin-expressing lymphocytes could be identified. In contrast, lymphocytes from patients who were receiving high doses of immunosuppressant did not contain any granzyme A- or perforin-expressing lymphocytes. Synovial fluid lymphocytes from patients with osteoarthritis did not express either marker. The expression of these markers demonstrates the presence of potentially functional cytolytic lymphocytes, expressing proteins required to mediate killing, in the synovial fluid of patients with rheumatoid arthritis. This suggests that cytolytic lymphocytes may be involved in the pathogenesis of rheumatoid arthritis.

Expression of T-cell-associated serine proteinase 1 during murine Leishmania major infection correlates with susceptibility to disease

The expression of T-cell-associated serine proteinase 1 (MTSP-1) in vivo during Leishmania major infection was analyzed in genetically resistant C57BL/6 mice and in genetically susceptible BALB/c mice. Using a monoclonal antibody as well as an RNA probe specific for MTSP-1 to stain tissue sections, we found T cells expressing MTSP-1 in skin lesions and spleens of mice of both strains. In skin lesions, MTSP-1-positive T cells could be detected as early as 3 days after infection. Most importantly, the frequency of T cells expressing MTSP-1 was significantly higher in susceptible BALB/c mice than in resistant C57BL/6 mice. These findings suggest that MTSP-1 is associated with disease-promoting T cells and that it may be an effector molecule involved in the pathogenesis of cutaneous leishmaniasis.

Expression of perforin and granzymes in vivo: potential diagnostic markers for activated cytotoxic cells

Perforin and granzymes are considered to be instrumental in cell-mediated cytolysis by cytotoxic T cells and natural killer cells. Here, Gillian Griffiths and Christoph Mueller describe the expression of perforin and granzymes, emphasizing studies in vivo, and discuss the possibility that these proteins are useful diagnostic markers for immune responses involving cytolytic cells.

Expression of perforin in infiltrating cells in murine hearts with acute myocarditis caused by coxsackievirus B3

BACKGROUND

Cell-mediated autoimmunity has been strongly implicated in the pathogenesis of viral myocarditis.

METHODS AND RESULTS

Using a murine model of acute myocarditis caused by coxsackievirus B3, we analyzed the phenotypes and morphology of the infiltrating cells in the hearts by immunofluorescence and electron microscopy. We also examined the expression of a cytolytic factor, perforin, in the infiltrating cells by immunoperoxidase and in situ hybridization. We found that the dominant population of the infiltrating cells were asialo GM1 positive, were negative for T-cell markers, and had electron-dense cytoplasmic granules, which is consistent with a morphology of large granular lymphocytes. Perforin was found in the cytoplasmic granules of the infiltrating cells expressing perforin messenger RNA. These findings provide for the first time the direct evidence that the first wave of cell infiltration in hearts mainly consists of killer cells and strongly suggests that perforin plays, in part, an important role in myocardial cell damage involved in acute viral myocarditis. T-helper cells and cytotoxic T lymphocytes made up the second wave of cell infiltration.

CONCLUSIONS

As we previously reported, the expression of major histocompatibility complex class I antigen on cardiac myocytes induced by the infiltrating cells, such as killer cells, may facilitate the interaction between cardiac myocytes and cytotoxic T lymphocytes, and may lead to further myocardial cell damage in a later phase.