Urinary granzyme A mRNA is a biomarker to diagnose subclinical and acute cellular rejection in kidney transplant recipients.

The distinction between T-cell-mediated rejection (TCMR) and other causes of kidney transplant dysfunction such as tubular necrosis requires biopsy. Subclinical rejection (SCR), an established risk factor for chronic allograft dysfunction, can only be diagnosed by protocol biopsy. A specific non-invasive biomarker to monitor immunological graft status would facilitate diagnosis and treatment of common transplantation-related complications. To identify possible markers, we measured urinary mRNA levels of several cytolytic proteins by quantitative PCR. Our cohort of 70 renal transplant recipients had biopsy proven type I and type II TCMR, acute tubular necrosis, SCR, calcineurin inhibitor-toxicity, cytomegalovirus infection, and stable graft function with normal histology. Granzyme A (GzmA) mRNA was significantly higher in subclinical and acute cellular rejection compared to patients with stable grafts or those with tubular necrosis with 80% sensitivity and up to 100% specificity. Granzyme B and perforin mRNA levels could significantly discriminate acute rejection from stable or tubular necrosis, but were not significantly elevated during SCR. Importantly, only GzmA mRNA remained below detection limits from grafts that were stable and most with tubular necrosis. Hence, the presented data indicate that urinary GzmA mRNA levels may entail a diagnostic non-invasive biomarker to distinguish patients with subclinical and acute cellular rejection from those with tubular necrosis or stable grafts.

Human mast cells produce and release the cytotoxic lymphocyte associated protease granzyme B upon activation.

Mast cells are widely distributed throughout the body and express effector functions in allergic reactions, inflammatory diseases, and host defense. Activation of mast cells results in exocytosis of preformed chemical mediators and leads to novel synthesis and secretion of lipid mediators and cytokines. Here, we show that human mast cells also express and release the cytotoxic lymphocyte-associated protease, granzyme B. Granzyme B was active and localized in cytoplasmic granules, morphologically resembling those present in cytotoxic lymphocytes. Expression and release of granzyme B by mast cell-lines HMC-1 and LAD 2 and by cord blood- and mature skin-derived human mast cells depended on the mode of activation of these cells. In mast cell lines and cord blood-derived mast cells, granzyme B expression was mainly induced by non-physiological stimuli (A23187/PMA, Compound 48/80) and substance P. In contrast, mature skin-derived mast cells only produced granzyme B upon IgE-dependent stimulation. We conclude that granzyme B is expressed and released by human mast cells upon physiologic stimulation. This suggests a role for granzyme B as a novel mediator in mast cell biology.

The granzyme B inhibitor SERPINB9 (protease inhibitor 9) circulates in blood and increases on primary cytomegalovirus infection after renal transplantation.

SERPINB9 is the only known human intracellular inhibitor of granzyme B (GrB), the effector molecule in immunity against cytomegalovirus (CMV) and in renal allograft rejection. Therefore, using specific enzyme-linked immunosorbent assays, we addressed the presence of circulating SERPINB9 during primary CMV infection, subclinical rejection, acute rejection, and uncomplicated posttransplantation course. Soluble (s) SERPINB9 circulates in blood and increases on primary CMV infection. This increase was significantly higher in symptomatic than in asymptomatic patients. In contrast, sSERPINB9 levels did not change in response to subclinical or acute rejection. We demonstrated the presence of circulating sSERPINB9/sGrB complexes, which suggests that SERPINB9 has extracellular functions as well.

The granzyme B inhibitor proteinase inhibitor 9 (PI9) is expressed by human mast cells.

The activity of granzyme B, a main effector molecule of cytotoxic T lymphocytes (CTL) and natural killer cells, is regulated by the human intracellular serpin proteinase inhibitor 9 (PI9). This inhibitor is particularly expressed by CTL and dendritic cells, in which it serves to protect these cells against endogenous and locally released granzyme B. Moreover, PI9 expression by neoplastic cells may constitute one of the mechanisms for tumors to escape immune surveillance. Here we show that PI9 is also expressed by human mast cells. In immunohistochemical studies using a PI9-specific monoclonal antibody, strong cytoplasmic staining for PI9 was found in normal mast cells in various tissues throughout the body. In addition, in 80% of all cases of cutaneous and systemic mastocytosis tested the majority of the mast cells expressed PI9. As an in vitro model for PI9 expression by mast cells, we studied expression by the human mast cell line HMC-1. Stimulation of HMC-1 with PMA and the calcium ionophore A23187 resulted in a marked increase of PI9 expression. Thus, PI9 is expressed by activated mast cells. We suggest that this expression serves to protect these cells against apoptosis induced by granzyme B released during initiation of the local inflammatory response.

Production, characterization, and use of serpin antibodies.

Serine protease inhibitors (serpins) constitute a still expanding superfamily of structural similar proteins, which are localized extracellularly and intracellularly. Serpins play a central role in the regulation of a wide variety of (patho) physiological processes including coagulation, fibrinolysis, inflammation, development, tumor invasion, and apoptosis. Serpins have a unique mechanism of inhibition that involves a profound change in conformational state upon interaction with their protease. This conformational change enables the production of monoclonal antibodies specific for native, complexed, and inactivated serpins. Antibodies, and assays based on these antibodies, have been helpful in elucidating the (patho) physiological function of serpins in the last decade. Serpin-specific antibodies can be used for: (1) structure-function studies such as detection of conformational changes; (2) identification of target-proteases; (3) the detection and quantification of serpin and serpin-protease complexes in bodily fluids by immunoassays such as ELISA, RIA or FACS; (4) detection of serpins in tissues by immunohistochemistry; and (5) possible therapeutical interventions. This review summarizes the techniques we have used to obtain and screen antibodies against extra- and intracellular serpins, as well as the use of these antibodies for some of the above-mentioned purposes.

Intracellular serpin SERPINB6 (PI6) is abundantly expressed by human mast cells and forms complexes with beta-tryptase monomers.

SERPINB6 (PI6) is a member of the intracellular serine protease inhibitors (serpins). Previous studies showed that SERPINB6 is localized mainly in the cytoplasm of endothelial cells, some epithelial cells, monocytes, and neutrophils. In these cells SERPINB6 is thought to prevent cellular damage by scavenging leaking lysosomal proteases. We show here, using novel, well-defined monoclonal antibodies, that SERPINB6 is abundantly expressed by mast cells in all organs and by the human mast cell line HMC-1. Gel filtration experiments revealed that the latter cells contain a high-molecular-weight form of SERPINB6, which consists of sodium dodecyl sulfate (SDS)-stable complexes of this inhibitor with monomeric beta-tryptase. Expression of SERPINB6 by mast cells was compared with those of tryptase and CD117 (c-kit) in biopsies from patients with different forms of mast cell disease. In all cases the lesional mast cells expressed SERPINB6, and, in diffuse cutaneous mastocytosis and mastocytoma, SERPINB6 was expressed by a substantially higher number of mast cells when compared with tryptase. In conclusion, SERPINB6 is abundantly expressed by normal mast cells and by mast cells in mastocytoma lesions. We suggest that in mast cells, SERPINB6 serves to regulate the activity of endogenous beta-tryptase in the cytoplasm.

Cancer-associated cleavage of cytokeratin 8/18 heterotypic complexes exposes a neoepitope in human adenocarcinomas.

The intermediate filament network in simple glandular epithelial cells predominantly consists of heterotypic complexes of cytokeratin 8 (K8) and cytokeratin 18 (K18). In contrast to other cytokeratins, K8 and K18 are persistently expressed during malignant transformation, but changes in cell morphology are accompanied by alterations in the intermediate filament network. To study molecular changes, K8 and K18 were purified from surgically removed colon cancer and normal epithelia tissues. Western blotting and amino acid sequencing revealed the presence of abundant K8 and K18 fragments, truncated at the N terminus, from cancerous, but not normal, epithelial cells. The fragmentation pattern indicates proteolysis mediated by several enzymes, including trypsin-like enzymes. The cancer-associated forms of K8 and K18 are specifically recognized by the human antibody, COU-1, cloned from the B cells of a cancer patient. We demonstrate that COU-1 recognizes a unique conformational epitope presented only by a complex between K8 and K18. The epitope is revealed after proteolytic removal of the head domain of either K8 or K18. A large panel of recombinant K8 and K18 fragments, deleted N- or C-terminally, allowed for the localization of the COU-1 epitope to the N-terminal part of the rod domains. Using surface plasmon resonance, the affinity of COU-1 for this epitope was determined to be 10(9) x m(-1), i.e. more than 2 orders of magnitude higher than for intact heterotypic K8/K18 complexes. The cellular distribution of truncated K8/K18 heterotypic complexes in viable adenocarcinomas cells was probed using COU-1 showing small fibrillar structures distinct from those of intact K8/K18 complexes. Previously we demonstrated the binding and subsequent internalization of recombinant Fab COU-1 to live cancer cells. We have thus characterized a cancer neoepitope recognized by the humoral immune system. The results have biological as well as clinical implications.