Role Of Granzyme Research Articles

Macrophages express granzyme B in the lesion areas of atherosclerosis and rheumatoid arthritis

Granzyme B is a major mediator of the cytotoxic immune response by inducing target cell death when internalized in the presence of perforin. Recently, several studies have focused on another role of granzyme B, which is extracellular matrix (ECM) remodeling through the degradation of ECM proteins. In order to investigate the expression pattern of granzyme B in the lesion areas of atherosclerosis and rheumatoid arthritis, we performed immunohistochemistry and in situ hybridization analyses using human atherosclerotic plaques and the synovial tissues of rheumatoid arthritic- and osteoarthritic-joints. In atherosclerotic plaques, granzyme B was expressed by macrophages in areas such as the boundary regions between media and intima, areas around necrotic cores, and in shoulder regions. In the synovial tissues of rheumatoid arthritic-joints, the expression of granzyme B was strongly observed in the lining layers where the majority of cells are macrophages and also in perivascular areas where macrophages and a small number of lymphocytes were mixed to form diffuse cellular aggregates. Granzyme B-positive cells were not detected in osteoarthritic synovium. Furthermore, the expression of granzyme B has been induced in the human macrophage cell line, THP-1, by ECM proteins or agents which induce macrophage differentiation. These observations indicate that macrophages should be added to the list of cell types that express granzyme B in human inflammatory diseases and that granzyme B may play a role in macrophage functions that are associated with disease progression.

Differential Expression of Granzymes A and K in Subsets of Human T-Cells and NK-Cells.

Granzymes are highly specific proteases stored in secretory granule in T-cells and NK-cells. Five different granzymes are known in human (A, B, H, K and M). A and B are the best studied and both can induce apotosis when delivered to target cells. The role for granzyme H, K and M are principally unknown. We have studied the expression of granzymes in subsets of T-cells and NK-cells both in fresh circulating cells and cultured cells stimulated with IL-2, IL-15 and OKT3/antiCD28. Protein expression (biosynthesis/immunoprecipitation) and mRNA level (RT-PCR) was studied in parallel. This report focus on Granzyme A and K which are close relatives, both tryptases located 70 kb apart on chromosome 5.Granzyme A have the highest expression in NK-cells were granzyme K are barely detected. Granzyme K on the other hand have a particular high expression in CD8+ T cells. Stimulation with IL-2 or IL-15 give a strong upregulation of both enzymes in NK-cells. Stimulation of CD8+ T cells gives mainly upregulation of granzyme A. Fresh CD4+ T cells show very weak synthesis of granzymes but treatment with IL-2 or IL-15 give a clear upregulation of both granzyme A and K. T-cells (both CD4+ and CD8+) are highly responsive to stimulation with OKT3/anti CD28 producing granzyme B but not A and K. This rather discordant pattern of expression for granzyme A and K talks in favour of different modes of regulation and most likely different functions.A striking difference between granzyme A and K concern the propensity for granzyme A to be secreted into the culture medium after stimulation while this is not the case for granzyme K. The secreted form of granzyme A has a molecular weight slightly higher than the intracellular form indicating the presence of a proform. Secretion of granzymes to the extracellular medium is probably not only an in vitro phenomena since both granzyme A and B can be detected in serum from healthy individuals in picomolar concentrations. Moreover, significant elevation of granzyme levels in serum can bee seen in different diseases with activation of cellular immunity and in T- and NK-cells malignancies. We have previously reported that proforms of certain serine proteases including the five human granzymes have a downregulating activity on myeloid proliferation, a mechanism probably implicated in certain forms of neutropenia. We propose that secreted granzymes (especially A, B and H) constitute a part of T regulatory function working both locally at the site of inflammation and distantly via the circulation.

Granzyme B and natural killer (NK) cell death

Granzyme B is a unique serine protease, which plays a crucial role for target cell death. Several mechanisms of delivery of granzyme B to target cells have been recently identified. Granzyme B directly activates Bid, a specific substrate for granzyme B, resulting in caspase activation. Granzyme B efficiently cleaves many prominent autoantigens, and the hypothesis that autoantibodies arise when cryptic determinants are revealed to the immune system has been proposed. Some autoantibodies directed against granzyme B-specific neoepitopes are present in serum from patients with autoimmune diseases. In the tissues from autoimmune diseases, granzyme B might play an important role for disease progression (i.e., rheumatoid arthritis synovium) or inhibition (i.e., regulatory T cells). We have identified a novel type of activation-induced cell death (granzyme B leakage-induced cell death). Activation-induced natural killer (NK) cell death is accompanied by the leakage of granzyme B from intracellular granules into the cytoplasm, and it triggers apoptosis by directing Bid to mitochondrial membranes. An excess of "leaked" granzyme B over its inhibitor, serpin proteinase inhibitor 9, is a major determinant of cell death. The role of granzyme B in autoimmunity and its influence on NK cell death are discussed.

Selective Chemical Functional Probes of Granzymes A and B Reveal Granzyme B Is a Major Effector of Natural Killer Cell-Mediated Lysis of Target Cells

The mechanism of target cell lysis in cytotoxic lymphocyte-mediated death is not well understood, and the role of granzymes in this process is unclear. Chemical functional probes were thus prepared for the major granzymes A and B to deconvolute their role in natural killer cell-mediated lysis of target cells. These biotinylated and substrate specificity-based diphenyl phosphonates allowed facile evaluation of selectivity through activity-based profiling in cell lysates and intact cells. Both inhibitors were found to be extremely selective in vitro and in cells. Use of these inhibitors in cell-based assays revealed granzyme A to be a minor effector and granzyme B to be a major effector of target cell lysis by natural killer cells. These studies indicate that the proapoptotic granzyme B functions also as a pronecrotic effector of target cell death.

Discordant Regulation of Granzyme H and Granzyme B Expression in Human Lymphocytes

We analyzed the expression of granzyme H in human blood leukocytes, using a novel monoclonal antibody raised against recombinant granzyme H. 33-kDa granzyme H was easily detected in unfractionated peripheral blood mononuclear cells, due to its high constitutive expression in CD3(-)CD56(+) natural killer (NK) cells, whereas granzyme B was less abundant. The NK lymphoma cell lines, YT and Lopez, also expressed high granzyme H levels. Unstimulated CD4(+) and particularly CD8(+) T cells expressed far lower levels of granzyme H than NK cells, and various agents that classically induce T cell activation, proliferation, and enhanced granzyme B expression failed to induce granzyme H expression in T cells. Also, granzyme H was not detected in NK T cells, monocytes, or neutrophils. There was a good correlation between mRNA and protein expression in cells that synthesize both granzymes B and H, suggesting that gzmH gene transcription is regulated similarly to gzmB. Overall, our data indicate that although the gzmB and gzmH genes are tightly linked, expression of the proteins is quite discordant in T and NK cells. The finding that granzyme H is frequently more abundant than granzyme B in NK cells is consistent with a role for granzyme H in complementing the pro-apoptotic function of granzyme B in human NK cells.

The role of granzyme B cluster proteases in cell-mediated cytotoxicity

Granzymes are neutral serine proteases that are stored in the specialized lytic granules of cytotoxic lymphocytes. A mutation introduced into the granzyme B locus leads to a severe defect in the ability of cytotoxic lymphocytes to induce apoptosis in susceptible target cells, and reduces the severity of class I-dependent acute graft-versus-host disease (GvHD). However, granzyme B-independent cytotoxicity also exists: in CD8+cells, most of it is perforin-dependent, but in CD4+cells, the Fas system and an additional pathway are involved. The identification of these pathways and their physiological relevance may lead to new approaches for inhibiting cytotoxic lymphocyte functions.

The Role of Granzyme B in Murine Models of Acute Graft-Versus-Host Disease and Graft Rejection

A complete molecular description of the syndromes of graft-versus-host disease (GVHD) and graft rejection could have a significant impact on clinical bone marrow transplantation. Recent in vitro experiments (Heusel et al, Cell 76:977, 1994 and Shresta et al, Proc Natl Acad Sci USA 92:5679, 1995) have shown that the putative mediators of these two syndromes, cytotoxic lymphocytes (CTL) and natural killer (NK) cells, respectively, initiate a program of cell death (apoptosis) in susceptible target tissues in a manner critically dependent on the serine protease Granzyme B (gzm B). In the present study, we have analyzed the phenotype of gzm B-deficient mice using experimental transplant models designed to isolate their CD8+ CTL, CD4+ CTL, and NK compartments. We found a significant impairment in class I-dependent GVHD mediated by gzm B -/- CD8+ CTL, whereas class II-dependent GVHD was not altered using gzm B -/- CD4+ effectors. In a hybrid resistance model, gzm B -/- hosts rejected haplo-identical marrow grafts as efficiently as did their wild-type littermates. This result is surprising in light of a severe defect in the ability of gzm B -/- NK cells to induce apoptosis in susceptible targets in vitro. These in vivo data define significant role for gzm B in cytotoxicity mediated by CD8+ CTL, but not by CD4+ CTL. Furthermore, these results do not support a model of hybrid resistance in which NK cells play a pivotal role.