Perforin and lymphocyte-mediated cytolysis

Mice lacking perforin have improved regeneration of the injured femoral nerve

The role that the immune system plays after injury of the peripheral nervous system is still not completely understood. Perforin, a natural killer cell- and T-lymphocyte-derived enzyme that mediates cytotoxicity, plays important roles in autoimmune diseases, infections and central nervous system trauma, such as spinal cord injury. To dissect the roles of this single component of the immune response to injury, we tested regeneration after femoral nerve injury in perforin-deficient (Pfp^–/–) and wild-type control mice. Single frame motion analysis showed better motor recovery in Pfp^–/– mice compared with control mice at 4 and 8 weeks after injury. Retrograde tracing of the motoneuron axons regrown into the motor nerve branch demonstrated more correctly projecting motoneurons in the spinal cord of Pfp^–/– mice compared with wild-types. Myelination of regrown axons measured by g-ratio was more extensive in Pfp^–/– than in wild-type mice in the motor branch of the femoral nerve. Pfp^–/– mice displayed more cholinergic synaptic terminals around cell bodies of spinal motoneurons after injury than the injured wild-types. We histologically analyzed lymphocyte infiltration 10 days after surgery and found that in Pfp^–/– mice the number of lymphocytes in the regenerating nerves was lower than in wild-types, suggesting a closed blood-nerve barrier in Pfp^–/– mice. We conclude that perforin restricts motor recovery after femoral nerve injury owing to decreased survival of motoneurons and reduced myelination.

Perforin affects regeneration in a mouse spinal cord injury model

MATERIALS AND METHODS

Locomotor outcomes in perforin-deficient (Pfp-/-) mice and wild-type littermate controls were measured after severe compression injury of the lower thoracic spinal cord up to six weeks after injury.

RESULTS

According to both the Basso mouse scale score and single frame motion analysis, motor recovery of Pfp-/- mice was similar to wild-type controls. Interestingly, immunohistochemical analysis of cell types at six weeks after injury showed enhanced cholinergic reinnervation of spinal motor neurons caudal to the lesion site and neurofilament-positive structures at the injury site in Pfp-/- mice, whereas numbers of microglia/macrophages and astrocytes were decreased compared with controls.

CONCLUSIONS

We conclude that, although, loss of perforin does not change the locomotor outcome after injury, it beneficially affects diverse cellular features, such as number of axons, cholinergic synapses, astrocytes and microglia/macrophages at or caudal to the lesion site. Perforin's ability to contribute to Rag2's influence on locomotion was observed in mice doubly deficient in perforin and Rag2 which recovered better than Rag2-/- or Pfp-/- mice, suggesting that natural killer cells can cooperate with T- and B-cells in spinal cord injury.

Physiological and functional aspects of metal-binding protein associated with mercury in the liver tissue of pirarucu (Arapaima gigas) from the Brazilian Amazon

High concentrations of mercury found in soils, sediments, fish, and humans of the Amazon region have gained prominence in scientific studies during the last decade. However, studies related to the elucidation of mercury toxicity mechanisms in ichthyofauna at the molecular and metallomic levels that seek to elucidate physiological and functional aspects, as well as the search for biomarkers of mercury exposure, are still sparse. In the search for these answers, the present study analyzed the hepatic tissue proteome of the Arapaima gigas (pirarucu) fish species collected in the Jirau hydroelectric power plant reservoir in the state of Rondônia state, Brazil, in order to identify mercury-related metal-binding proteins and to elucidate their physiological and functional aspects. The proteomic profile of the hepatic tissue of Arapaima gigas was obtained by two-dimensional electrophoresis (2D-PAGE) and the presence of mercury was mapped in the protein SPOTS by graphite furnace atomic absorption spectrometry(GFAAS). Mercury was detected in 18 protein SPOTS with concentrations ranging from 0.13 ± 0.003 to 131.00 ± 3 mg kg^-1. The characterization of the protein SPOTS associated with mercury was performed by electrospray ionisation tandem mass spectrometry (ESI-MS/MS), and 10 proteins were identified. Bioinformatics analyses showed that most of the proteins found linked to mercury were involved in cellular component processes and biological processes. For the most part, protein sequences have cellular functions comprising catalytic, binding, sense of localization, and metabolic processes.

Modulation of Apoptosis by Cytotoxic Mediators and Cell-Survival Molecules in Sjögren's Syndrome

The pathogenesis of Sjögren’s syndrome (SS) involves multiple factors including genetic background, cell death, and exocrine dysfunction. We here discuss apoptotic control in exocrine glands in SS by showing various pro- and anti-apoptotic pathways. Although the membrane-bound and soluble form of the Fas/Fas ligand system is a leading player with activation of the death domain and caspase 8/3 cleavage, the role of soluble Fas/FasL (including its polymorphism) in apoptosis is controversial. The tumor necrosis factor related apoptosis-inducing ligand (TRAIL)-mediated apoptosis of salivary gland epithelial cells (SGECs) involves a mitochondrial pathway that includes caspase 9 cleavage. The involvement of innate immunity cells such as toll-like receptors (TLRs) has been investigated; TLR2-4 and TLR7-9 are associated with the induction of inflammation in exocrine glands of SS patients. TLR3 has the potential to induce the apoptosis of SS patients’ SGECs. Linkage of epidermal growth factor (EGF) was shown in exocrine glands in SS, and it inhibited the Fas/FasL system with the help of cell-survival factors. TLR3 has dual actions to cause inflammation as well as apoptosis, which are inhibited by EGF. In conclusion, apoptosis in exocrine glands of SS patients is tightly controlled by balance of pro-apoptotic signals and growth factor.

The role of BST-2/Tetherin in host protection and disease manifestation

Host cells respond to viral infections by activating immune response genes that are not only involved in inflammation, but may also predispose cells to cancerous transformation. One such gene is BST‐2, a type II transmembrane protein with a unique topology that endows it tethering and signaling potential. Through this ability to tether and signal, BST‐2 regulates host response to viral infection either by inhibiting release of nascent viral particles or in some models inhibiting viral dissemination. However, despite its antiviral functions, BST‐2 is involved in disease manifestation, a function linked to the ability of BST‐2 to promote cell‐to‐cell interaction. Therefore, modulating BST‐2 expression and/or activity has the potential to influence course of disease.

Expression of endometrial immune-related genes possibly functioning during early pregnancy in the mare

Despite enormous efforts, biochemical and molecular mechanisms associated with equine reproduction, particularly processes of pregnancy establishment, have not been well characterized. Previously, PCR-selected suppression subtraction hybridization analysis was executed to identify unique molecules functioning in the equine endometrium during periods of pregnancy establishment, and granzyme B (GZMB) cDNA was found in the pregnant endometrial cDNA library. Because GZMB is produced from natural killer (NK) cells, endometrial expression of GZMB and immune-related transcripts were characterized in this study. The level of GZMB mRNA is higher in the pregnant endometrium than in non-pregnant ones. This expression was also confirmed through Western blot and immunohistochemical analyses. IL-2 mRNA declined as pregnancy progressed, while IL-15, IFNG and TGFB1 transcripts increased on day 19 and/or 25. Analyses of IL-4 and IL-12 mRNAs demonstrated the increase in these transcripts as pregnancy progressed. Increase in CCR5 and CCR4 mRNAs indicated that both Th1 and Th2 cells coexisted in the day 25 pregnant endometrium. Taken together, the endometrial expression of immune-related transcripts suggests that immunological responses are present even before the trophectoderm actually attaches to the uterine epithelial cells.

Assessment of different biomarkers provides valuable diagnostic standards in the evaluation of the risk of acute rejection

Acute rejection (AR) is a strong risk factor for chronic rejection in renal transplant recipients. Accurate and timely diagnosis of AR episodes is very important for disease control and prognosis. Therefore, objectively evaluated the immune status of patients is essential in the field of post-transplantation treatment. This longitudinal study investigated the usefulness of five biomarkers, human leukocyte antigen (HLA)-G5 and sCD30 level in sera, intracellular adenosine triphosphate (iATP) release level of CD4(+) T cells, and granzyme B/perforin expression in peripheral blood mononuclear cells (PBMCs) and biopsies, to detect AR and the resolution of biomarkers in a total of 84 cases of renal transplantation. The data demonstrated that recipients with clinical or biopsy proven rejection significantly increased iATP release level of CD4(+) T cells, and elevated sCD30 but lowered HLA-G5 level in sera compared with individuals with stable graft function. Expression levels of granzyme B and perforin were also elevated in PBMCs and graft biopsies of AR patients. Taken together, we identified that upregulation of sCD30, iATP, granzyme B, perforin, and downregulation of HLA-G5 could provide valuable diagnostic standards to identify those recipients in the risk of AR. And iATP may be a better biomarker than others for predicting the graft rejection episode.

Cellular and molecular requirements for rejection of B16 melanoma in the setting of regulatory T cell depletion and homeostatic proliferation

We have recently demonstrated that adoptive transfer of regulatory T cell-depleted polyclonal T cells into lymphopenic mice leads to rejection of B16 melanoma, which generated an opportunity to study host requirements for tumor rejection when it effectively occurred. CD8(+) T cell priming and tumor rejection required tumor Ag cross-presentation, as evidenced by tumor outgrowth in Kb(-/-) bone marrow chimeric or B71/2(-/-) mice. CD4(+) T cells were additionally required for optimal tumor control, although not through classical CD4 "help," as the frequency of primed CD8(+) T cells was similar in the absence of CD4(+) T cells, and tumor rejection did not depend upon CD40-CD40L interactions or on IL-2 production by CD4(+) T cells. Rather, CD4(+) T cells appeared to act at the effector phase of tumor rejection and responded to B16-derived Ags in vitro. At the effector phase, IFN-γ production by transferred T cells, but not host cells, was necessary. IFN-γ acted either on host or tumor cells and was associated with reduced tumor vascularity. Finally, tumor rejection occurred after transfer of TNF-α, perforin, or FasL-deficient T cells. However, perforin/FasL double-knockout T cells failed to reject, arguing that the killing of B16 melanoma cells could occur either via the cytotoxic granule or Fas pathways. Collectively, these results support a model in which host tumor Ag cross-presentation primes adoptively transferred T cells, which remain functional in the setting of homeostatic proliferation and regulatory T cell depletion, and which promote tumor rejection via IFN-γ and lysis via cytotoxic granules and/or FasL.

Alveolar macrophage gene expression is altered in the setting of alcohol use disorders

BACKGROUND

Alcohol use disorders (AUDs) are associated with an increased susceptibility to a variety of common and devastating pulmonary diseases including community- and hospital-acquired pneumonias, as well as the acute respiratory distress syndrome (ARDS). Alveolar macrophages play an important role in preventing the development of these disorders through maintaining lung sterility and resolving lung inflammation. Although alcohol exposure has been associated with aberrant alveolar macrophage function in animal models, the clinical relevance of these observations in humans is not established. Therefore, we sought to determine the effects of AUDs on human alveolar macrophage gene expression.

METHODS

Whole genome microarray analysis was performed on alveolar macrophages obtained by bronchoalveolar lavage from a test cohort of subjects with AUDs (n = 7), and controls (n = 7) who were pair-matched on age, gender, and smoking. Probe set expression differences in this cohort were validated by real-time reverse transcription-polymerase chain reaction (RT RT-PCR). Functional analysis with web-based bioinformatics tools was utilized with microarray data to assess differentially expressed candidate genes (p < 0.01) based on alcohol consumption. Alveolar macrophage mRNA samples from a second cohort of subjects with AUDs (n = 7) and controls (n = 7) were used to confirm gene expression differences related to AUDs.

RESULTS

In both the test and the confirmatory cohorts, AUDs were associated with upregulation of alveolar macrophage gene expression related to apoptosis, including perforin-1, granzyme A, and CXCR4 (fusin). Pathways governing the regulation of progression through cell cycle and immune response were also affected, as was upregulation of gene expression for mitochondrial superoxide dismutase. Overall, 12 genes' expression was affected by AUDs independent of smoking.

CONCLUSIONS

Alcohol use disorders are associated with unique changes in human alveolar macrophage gene expression. Novel therapies targeting alveolar macrophage gene expression in the setting of AUDs may prove to be clinically useful in limiting susceptibility for pulmonary disorders in these individuals.

Etanercept reduces the serum levels of macrophage chemotactic protein-1 in patients with rheumatoid arthritis

This study was performed to analyze the effect of etanercept, the soluble tumor necrosis factor-alpha (TNF-alpha) receptor, on the serum levels of several chemokines including monocyte chemotactic protein-1 (MCP-1), regulated upon activation normal T expressed and presumably secreted (RANTES), and granzyme B in rheumatoid arthritis (RA) patients. Twenty-eight patients with RA were administered etanercept once or twice a week for more than 6 months. Clinical and laboratory parameters were measured and serum levels of MCP-1, RANTES, and granzyme B were determined using enzyme-linked immunosorbent assay (ELISA) kits at baseline and at 3 and 6 months after the initial treatment. In addition, the levels of MCP-1, RANTES, and granzyme B produced by cultured synovial cells stimulated with TNF-alpha were measured. A significant decrease in serum MCP-1 levels was observed at 3 and 6 months after initial treatment with etanercept. Serum RANTES and granzyme B levels did not show significant changes. TNF-alpha induced MCP-1, RANTES, and granzyme B production in cultured synovial cells from RA patients. Serum MCP-1 levels were significantly correlated with the disease activity scores of 28 joints combined with CRP (DAS28-CRP), indicating the role of MCP-1 in the pathogenesis of rheumatoid inflammation. This study demonstrated that a reduction of MCP-1 production in RA patients was a newly determined effect of etanercept. Another cascade not associated with TNF-alpha may induce granzyme B and RANTES production in RA patients.

Granzyme C supports efficient CTL-mediated killing late in primary alloimmune responses

It is well established that granzymes A and B play a role in CTL killing of target cells by the perforin-dependent granule exocytosis pathway. The functions of multiple additional granzymes expressed in CTL are less well defined. In the present studies, CTL generated from mice deficient in dipeptidyl peptidase 1 (DPP1) were used to investigate the contribution of granzyme C to CTL killing of allogeneic target cells. DPP1 is required for activation of granzymes A and B by proteolytic removal of their N-terminal dipeptide prodomains while a significant portion of granzyme C is processed normally in the absence of DPP1. Cytotoxicity of DPP1(-/-) CTL generated in early (5-day) MLC in vitro and in peritoneal exudate cells 5 days after initial allogeneic sensitization in vivo was significantly impaired compared with wild-type CTL. Following 3 days of restimulation with fresh allogeneic stimulators however, cytotoxicity of these DPP1(-/-) effector cells was comparable to that of wild-type CTL. Killing mediated by DPP1(-/-) CTL following restimulation was rapid, perforin dependent, Fas independent and associated with early mitochondrial injury, phosphatidyl serine externalization, and DNA degradation, implicating a granzyme-dependent apoptotic pathway. The increased cytotoxicity of DPP1(-/-) CTL following restimulation coincided with increased expression of granzyme C. Moreover, small interfering RNA inhibition of granzyme C expression during restimulation significantly decreased cytotoxicity of DPP1(-/-) but not wild-type CTL. These results indicate that during late primary alloimmune responses, granzyme C can support CTL-mediated killing by the granule exocytosis pathway in the absence of functional granzymes A or B.

Helicobacter pylori augments growth of gastric cancers via the lipopolysaccharide-toll-like receptor 4 pathway whereas its lipopolysaccharide attenuates antitumor activities of human mononuclear cells

PURPOSE

Helicobacter pylori is reportedly involved in the development of gastric cancer. We investigated the mechanisms by which H. pylori affects gastric cancer growth and antitumor immunities in the host, focusing on H. pylori-derived lipopolysaccharide (LPS).

EXPERIMENTAL DESIGN

H. pylori and four gastric cancer cell lines (MKN28, MKN45, NUGC3, and KATOIII) were used. We examined the effect of H. pylori or its LPS stimulation on cancer growth and the involvement of the H. pylori LPS-toll-like receptor 4 (TLR4) pathway. We also examined the cytotoxicities of H. pylori/LPS-stimulated human mononuclear cells (MNC) against gastric cancer cells and the effect of H. pylori LPS stimulation on cytokine production by MNC.

RESULTS

H. pylori, as well as its LPS, augmented the growth of gastric cancers, all of which expressed TLR4. Neutralization of TLR4 almost completely abrogated the H. pylori-induced proliferative activity of cancer cells. Escherichia coli LPS also augmented cancer growth via the LPS-TLR4 pathway. However, only H. pylori-derived LPS attenuated the cytotoxicity of MNC against gastric cancer cells. Stimulation with H. pylori/LPS also down-regulated perforin production in cancer cell-cocultured CD56+ natural killer cells. H. pylori LPS induced neither interleukin-12 nor IFN-gamma production by MNC, although E. coli LPS did induce production of both significantly. Nevertheless, interleukin-12 stimulation restored the IFN-gamma-producing capacity of H. pylori LPS-stimulated MNC.

CONCLUSION

H. pylori augmented the growth of gastric cancers via the LPS-TLR4 pathway, whereas it attenuated the antitumor activity and IFN-gamma-mediated cellular immunity of MNC. H. pylori infection might thereby promote proliferation and progression of gastric cancers.

Innate immunity: a cutaneous perspective

The first responsibility for protection against microbial infection rests on the normal function of the innate immune system. This system establishes an antimicrobial barrier, recognizes attempts to breach this barrier, and responds rapidly to danger, all based on an innate defense system. Here, we review this system as it applies to mammalian skin, highlighting how a physical, cellular, and chemical barrier is formed to resist infection. When challenged, the diverse cellular components of the skin recognize the nature of the challenge and respond with an appropriate antimicrobial program including the release of antimicrobial peptides and, when necessary, recruitment and coordination with adaptive immune responses. Recent insights into these processes have advanced the understanding of disease pathogenesis and provided new therapeutic options for a variety of skin diseases.

Identification and characterization of equine granzyme B

In the present study we describe the isolation and characterization of putative equine granzyme B for which we propose the designation 'eqGrzmB'. Sequence analysis revealed characteristic features of a GrzmB protease such as the presence of a signal (leader-) peptide and an activation di-peptide. The isolated eqGrzmB is functionally active when expressed in human or in insect cells. Furthermore, exchange of any of three putative active site amino acids, which are highly conserved along granzyme B enzymes, led to a complete loss of enzymatic activity in the newly identified eqGrzmB. Phylogenetic analysis places eqGrzmB in the chymase-locus within the large family of granzymes in close proximity to putative equine mast cell protease and to granzyme B from mouse, rat, and human. eqGrzmB proteolytic activity has been kinetically characterized and can be specifically inhibited by granzyme B inhibitors. Taken together, we conclude that we have isolated a new member of the granzyme B family, the first granzyme identified in Equidae. The description of equine granzyme B might facilitate the development of immunological assays for the activity of equine lymphocytes.

Loss of Necrotic Spotted Lesions 1 associates with cell death and defense responses in Arabidopsis thaliana

We isolated a lesion mimic mutant, necrotic spotted lesions 1 (nsl1), from Ds-tagged Arabidopsis thaliana accession No-0. The nsl1 mutant exhibits a growth retardation phenotype and develops spotted necrotic lesions on its rosette and cauline leaves. These phenotypes occur in the absence of pathogens indicating that nsl1 mutants may constitutively express defense responses. Consistent with this idea, nsl1 accumulates high levels of callose and autofluorescent phenolic compounds localized to the necrotic lesions. Furthermore RNA gel blot analysis revealed that genes associated with disease resistance activation are upregulated in the nsl1 mutants and these plants contain elevated levels of salicylic acid (SA). Crossing nsl1 with an SA deficient mutant, eds16-1, revealed that the nsl1 lesions and growth retardation are dependent upon SA. The nsl1 phenotypes are not suppressed under either the rar1-10 or sgt1b-1 genetic background. NSL1 encodes a novel 612aa protein which contains a membrane-attack complex/perforin (MACPF) domain, which is conserved in bacteria, fungi, mammals and plants. The possible modes of action of NSL1 protein in negative regulation of cell death programs and defense responses are discussed.

Dendritic cell biology, dysfunction and immunotherapy in gastrointestinal cancers

Gastrointestinal (GI) cancers make up a significant proportion of newly diagnosed malignant disease. The five-year survival for these GI cancers is poor. Anti-cancer host defences are thought to play a role in these cancers, albeit they are suboptimal. Novel immunotherapies are being introduced to treat such patients. This review describes basic cell biology of dendritic cells, as they are thoughtto play a key role in generating effective anti-tumour responses. Dendritic cell dysfunction in patients with various cancers is documented and immunotherapy using dendritic cells in a range of GI cancers is described and discussed

Cytotoxic T lymphocyte-induced killing in the absence of granzymes A and B is unique and distinct from both apoptosis and perforin-dependent lysis

Cytotoxic T lymphocyte (CTL)–induced death triggered by the granule exocytosis pathway involves the perforin-dependent delivery of granzymes to the target cell. Gene targeting has shown that perforin is essential for this process; however, CTL deficient in the key granzymes A and B maintain the ability to kill their targets by granule exocytosis. It is not clear how granzyme AB^−/− CTLs kill their targets, although it has been proposed that this occurs through perforin-induced lysis. We found that purified granzyme B or CTLs from wild-type mice induced classic apoptotic cell death. Perforin-induced lysis was far more rapid and involved the formation of large plasma membrane protrusions. Cell death induced by granzyme AB^−/− CTLs shared similar kinetics and morphological characteristics to apoptosis but followed a distinct series of molecular events. Therefore, CTLs from granzyme AB^−/− mice induce target cell death by a unique mechanism that is distinct from both perforin lysis and apoptosis.

Identification of a Naegleria fowleri membrane protein reactive with anti-human CD59 antibody

Naegleria fowleri, the causative agent of primary amebic meningoencephalitis, is resistant to complement lysis. The presence of a complement regulatory protein on the surface of N. fowleri was investigated. Southern blot and Northern blot analyses demonstrated hybridization of a radiolabeled cDNA probe for CD59 to genomic DNA and RNA, respectively, from pathogenic N. fowleri. An 18-kDa immunoreactive protein was detected on the membrane of N. fowleri by Western immunoblot and immunofluorescence analyses with monoclonal antibodies for human CD59. Complement component C9 immunoprecipitated with the N. fowleri "CD59-like" protein from amebae incubated with normal human serum. In contrast, a gene or protein similar to CD59 was not detected in nonpathogenic, complement-sensitive N. gruberi amebae. Collectively, our studies suggest that a protein reactive with antibodies to human CD59 is present on the surface of N. fowleri amebae and may play a role in resistance to lysis by cytolytic proteins.

Exploitation of interleukin-18 by gastric cancers for their growth and evasion of host immunity

Interleukin-18 (IL-18) is a pleiotropic cytokine that enhances Th1 or Th2 immune response. We show a novel mechanism of gastric cancer cells that allows their immune escape utilizing IL-18. All 4 gastric cancer cell lines, but not colon lines, constitutively expressed IL-18 receptors and IL-18 dose-dependently enhanced their in vitro proliferation accompanied by nuclear factor kappaB activation. When IL-18-pretreated gastric cancer cells were cultured with cytokine-activated peripheral blood killer lymphocytes, the antitumor machineries, perforin or interferon-gamma production of killer lymphocytes decreased, resulting in a decreased susceptibility of cancer cells to killer lymphocytes. Furthermore, gastric cancer cells cultured with IL-18 showed an increased expression of a granzyme B inhibitor, protease inhibitor 9. IL-18 injections into severe combined immuno-deficient mice intraperitoneally inoculated with gastric cancer cells consistently decreased the mouse survival time. Our results indicate that gastric cancers exploit IL-18 to grow/invade and evade immunosurveillance in the hosts.

Antitumour activity mediated by CD4+ cytotoxic T lymphocytes against MHC class II-negative mouse hepatocellular carcinoma induced by dendritic cell vaccine and interleukin-12

When BALA/c mice with BNL hepatocellular carcinoma (HCC) were treated with dendritic cells fused with BNL cells (DC/BNL) and recombinant murine interleukin (IL)-12, tumour development was significantly suppressed, whereas treatment with either DC/BNL or IL-12 alone did not show a tumour-suppressive effect. Antitumour activity induced by DC/BNL + IL-12 was abrogated by depletion of CD4+ T cells, but not by depletion of CD8+ T cells or natural killer cells. Splenic CD4+ T cells and CD8+ T cells from DC/BNL-treated mice showed cytotoxic activity against BNL cells after 3 days of incubation with DC/BNL, although BNL cells do not express major histocompatibility complex (MHC) class II molecules even after treatment with interferon (INF)-gamma. Furthermore, CD4+ T cells killed syngeneic-irrelevant CT26 cells and even allogeneic Hepa1-6 cells. This cytotoxicity was blocked by concanamycin A, but not by an anti-Fas ligand (FasL) monoclonal antibody, indicating that cytotoxic activity was mediated by perforin. Immunofluorescence microscopy demonstrated that abundant CD4+ T cells and MHC class II-positive macrophages, but not CD8(+) T cells, had infiltrated tumour tissue in mice treated with DC/BNL + IL-12. Flow cytometric analysis of tumour-infiltrating cells in mice treated with DC/BNL + IL-12 showed increases in CD4+ T cells and MHC class II+ CD11b+ cells but not in CD8+ T cells or MHC class I+ CD11b+ cells. Our results suggest that, in BNL-bearing mice treated with DC/BNL + IL-12, tumour macrophages activated by INF-gamma produced by IL-12-stimulated T cells might present BNL tumour antigens and activate DC/BNL-primed CD4+ cytotoxic T lymphocytes (CTLs) in a MHC class II-dependent manner, leading to perforin-mediated bystander killing of neighbouring MHC class II-negative tumour cells.

Amyloid peptide channels

At least 16 distinct clinical syndromes including Alzheimer's disease (AD), Parkinson's disease (PD), rheumatoid arthritis, type II diabetes mellitus (DM), and spongiform encephelopathies (prion diseases), are characterized by the deposition of amorphous, Congo red-staining deposits known as amyloid. These "misfolded" proteins adopt beta-sheet structures and aggregate spontaneously into similar extended fibrils despite their widely divergent primary sequences. Many, if not all, of these peptides are capable of forming ion-permeable channels in vitro and possibly in vivo. Common channel properties include irreversible, spontaneous insertion into membranes, relatively large, heterogeneous single-channel conductances, inhibition of channel formation by Congo red, and blockade of inserted channels by Zn2+. Physiologic effects of amyloid, including Ca2+ dysregulation, membrane depolarization, mitochondrial dysfunction, inhibition of long-term potentiation (LTP), and cytotoxicity, suggest that channel formation in plasma and intracellular membranes may play a key role in the pathophysiology of the amyloidoses.

Modified ELISPOT

The use of the IFN-γ ELISPOT assay to evaluate cellular immune responses has gained increasing popularity, especially as a surrogate measure for CTL responses. We developed and validated some modifications of the IFN-γ ELISPOT assay to optimize immunological monitoring of various cancer vaccine trials. Taking into consideration that the main mechanism of cell-mediated cytotoxicity is the release of cytolytic granules that contain, among others, cytolytic protein Granzyme B (GrB), we developed the GrB ELISPOT assay. Extensive studies demonstrated that the GrB ELISPOT assay is specific, accurately measures the rapid release of GrB, is more sensitive than the 51Cr-release assay, and that it may be successfully applied to measuring CTL precursory frequency in PBMC from cancer patients. Assuming that immunological assays that demonstrate recognition of native tumor cells (tumor-specific) may be more clinically relevant than assays that demonstrate recognition of tumor protein or peptide (antigen-specific), we developed and validated the Autologous Tumor IFN-γ ELISPOT assay using PBMC from idiotype vaccinated lymphoma patients as effectors and autologous B cell lymphoma tumor cells as targets. The precursor frequency of tumor-reactive T cells was significantly higher in the postvaccine PBMC, compared with prevaccine samples in all patients tested. Furthermore, the specificity of these T cells was established by the lack of reactivity against autologous normal B cells. These results demonstrate the feasibility of evaluating tumor-specific T cell responses when autologous, primary tumor cells are available as targets. Modifications of ELISPOT assay described in this chapter allow more comprehensive assessment of low frequency tumor-specific CTL and their specific effector functions and can provide valuable insight with regards to immune responses in cancer vaccine trials.

Cytokines and cytotoxic pathways in engraftment resistance to purified allogeneic hematopoietic stem cells

The way that allogeneic hematopoietic cells are rejected is not completely understood. Regimen-resistant populations, including natural killer (NK) cells and lymphocytes, are thought to mediate the allograft barrier. In this report, the mechanism by which recipient cell populations resist engraftment of purified allogeneic hematopoietic stem cells (HSCs) was examined in mice. To define the immunoregulatory pathways involved in allogeneic hematopoietic cell resistance, HSC transplantations were performed in immune-defective recipients. Recipients were wild-type mice treated with alpha-NK cell antibodies or knockout strain mice lacking expression of CD8, perforin, Fas ligand, or 1 of the following cytokines: tumor necrosis factor alpha, transforming growth factor beta, interferon gamma, interleukin 4, or interleukin 10. Elimination of a single cytotoxic pathway was ineffective in reducing engraftment resistance, although mice treated with a polyclonal antibody that recognizes NK-cell determinants or CD8 expression showed a profound reduction in the engraftment barrier. Posttransplantation chimerism analysis revealed regeneration of host hematopoiesis in some experimental groups. These studies show, for the first time, that elimination of selected cytokines does not alter allogeneic hematopoietic resistance. Furthermore, the chimerism data reinforce the importance of competition for HSC niches in conjunction with immune mechanisms in resistance to long-term HSC engraftment.

Raised granzyme B levels are associated with erosions in patients with early rheumatoid factor positive rheumatoid arthritis

BACKGROUND

Raised granzyme B in serum and synovium of patients with rheumatoid arthritis suggests a role for cytotoxic T cells and natural killer cells in the pathogenesis of this disease.

OBJECTIVE

To evaluate serum granzyme B in patients with early arthritis and correlate it with specific diagnosis and clinical indices of disease severity.

METHODS

257 patients with inflammatory arthritis for less than one year (46% rheumatoid arthritis, 17% spondyloarthropathy, 37% undifferentiated arthritis) had a prospective clinical, serological, and radiographic evaluation. Granzyme B was measured in initial sera by ELISA. Patients were HLA typed for DR alleles using sequence specific primers. A logistic regression model was used to evaluate the potential prognostic value of serum granzyme B in predicting radiographic erosions after one year of follow up.

RESULTS

Granzyme B values were similar in rheumatoid arthritis, spondyloarthropathy, and undifferentiated arthritis. Concentrations were higher in rheumatoid factor (RF) positive patients than in RF negative patients (mean (SD): 3.15 (0.92) v 2.89 (0.71) pg/ml; p<0.05). After one year, erosions were present in 30% of patients in the overall cohort, and in 44% of patients with rheumatoid arthritis. In the entire cohort, serum granzyme B did not predict erosions independently. However, high granzyme B was an independent predictor of early erosions in patients with RF positive rheumatoid arthritis (odds ratio = 4.83 (95% confidence interval, 1.13 to 20.59)) (p<0.05).

CONCLUSIONS

Granzyme B may be a useful prognostic marker in early rheumatoid arthritis and may provide important clues to the pathogenesis of this disease.

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.

Anti-interleukin-2 receptor antibodies for the prevention of rejection in pediatric renal transplant patients: current status

The anti-interleukin-2 receptor (anti-IL-2R) antibody therapy is an exciting approach to the prevention of acute rejection after renal allograft transplantation whereby immunosuppression is exerted by a selective and competitive inhibition of IL-2-induced T cell proliferation, a critical pathway of allorecognition. The anti-IL-2R antibodies specifically block the alpha-subunit of the IL-2R on activated T cells, and prevent T cell proliferation and activation of the effector arms of the immune system. The anti-IL-2R antibodies are used as induction therapy, immediately after renal transplantation, for prevention of acute cellular rejection in children and adults. During acute rejection, the IL-2Ralpha chain is no longer expressed on T cells; thus, the antibodies cannot be used to treat an existing acute rejection. Two anti-IL-2R monoclonal antibodies are currently in clinical use: daclizumab and basiliximab. In placebo-controlled phase III clinical trials in adults, daclizumab and basiliximab in combination with calcineurin inhibitor-based immunosuppression, significantly reduced the incidence of acute rejection and corticosteroid-resistant acute rejection without increasing the risk of infectious or malignant complications, and neither antibody was associated with the cytokine-release syndrome. Children who receive calcineurin inhibitors and corticosteroids for maintenance immunosuppression, as well as children who receive augmented immunosuppression to treat acute rejection, are at increased risk of growth impairment, hypertension, hyperlipidemia, lymphoproliferative disorders, diabetes mellitus, and cosmetic changes. In older children, the cosmetic adverse effects frequently reduce compliance with the treatment, and subsequently increase the risk of allograft loss. Being effective and well tolerated in children, the anti-IL-2R antibodies reduce the need for calcineurin inhibitors while maintaining the overall efficacy of the regimen; thus, the anti-IL-2R antibodies increase the safety margin (less toxicity, fewer adverse effects) of the baseline immunosuppression. Secondly, the anti-IL-2R antibodies decrease the need for corticosteroids and muromonab CD3 (OKT3) in children as a result of decreased incidence of acute rejection. The recommended pediatric dose of daclizumab is 1 mg/kg intravenously every 14 days for five doses, with the first dose administered within 24 hours pre-transplantation. This administration regimen maintains daclizumab levels necessary to completely saturate the IL-2Ralpha (5-10 microg/mL) in children for at least 12 weeks.The recommended pediatric dose of basiliximab for recipients <35 kg is 10 mg, and 20 mg for recipients > or =35 kg, intravenously on days 0 and 4 post-transplantation. This administration regimen maintains basiliximab levels necessary to completely saturate the IL-2Ralpha (>0.2 microg/mL) in children for at least 3 weeks.

Natural killer cells and cancer

Natural killer (NK) cells are lymphocytes that were first identified for their ability to kill tumor cells without deliberate immunization or activation. Subsequently, they were also found to be able to kill cells that are infected with certain viruses and to attack preferentially cells that lack expression of major histocompatibility complex (MHC) class I antigens. The recent discovery of novel NK receptors and their ligands has uncovered the molecular mechanisms that regulate NK activation and function. Several activating NK cell receptors and costimulatory molecules have been identified that permit these cells to recognize tumors and virus-infected cells. These are modulated by inhibitory receptors that sense the levels of MHC class I on prospective target cells to prevent unwanted destruction of healthy tissues. In vitro and in vivo, their cytotoxic ability can be enhanced by cytokines, such as interleukin (IL)-2, IL-12, IL-15 and interferon alpha/beta (IFN-alpha/beta). In animal studies, they have been shown to play a critical role in the control of tumor growth and metastasis and to provide innate immunity against infection with certain viruses. Following activation, NK cells release cytokines and chemokines that induce inflammatory responses; modulate monocyte, dendritic cells, and granulocyte growth and differentiation; and influence subsequent adaptive immune responses. The underlining mechanism of discriminating tumor cells and normal cells by NK cells has provided new insights into tumor immunosurveillance and has suggested new strategies for the treatment of human cancer.

Atypical features of familial hemophagocytic lymphohistiocytosis

Familial hemophagocytic lymphohistiocytosis (FHLH) is a rare, rapidly progressive disorder of early childhood characterized by uncontrolled activation of T cells and macrophages. Although perforin gene mutations have been described in a proportion of patients with FHLH, the genotype/phenotype correlation is still limited. Only a few patients with late onset clinical manifestations have been reported. The biochemical and immunologic alterations in the asymptomatic phase are not well known. We report on a family in which 2 fraternal twins both homozygous for a perforin mutation previously described as causative of the disease, markedly differed in phenotypic expression of FHLH. The twins also had a second novel heterozygous mutation. Natural killer (NK) activity was severely impaired in the patient and was normal in the asymptomatic fraternal twin. Our report highlights that FHLH may present after a long disease-free interval during which biochemical or immunologic alterations may be not evident, thus implying a role for interfering factors.

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.

Perforin and gamma interferon are critical CD8+ T-cell-mediated responses in vaccine-induced immunity against Leishmania amazonensis infection

Previous studies have demonstrated that protection against New World leishmaniasis caused by Leishmania amazonensis can be elicited by immunization with the developmentally regulated Leishmania amastigote antigen, P-8. In this study, several independent experimental approaches were employed to investigate the protective immunological mechanisms involved. T-cell subset depletion experiments clearly indicate that elicitation of CD8(+) (as well as CD4(+)) effector responses is required for protection. Further, mice lacking beta(2)-microglobulin (and hence deficient in major histocompatibility complex class I antigen presentation) were not able to control a challenge infection after vaccination, indicating an essential protective role for CD8(+) T effector responses. Analysis of the events ongoing at the cutaneous site of infection indicated a changing cellular dynamic involved in protection. Early postinfection in protectively vaccinated mice, a predominance of CD8(+) T cells, secreting gamma interferon (IFN-gamma) and expressing perforin, was observed at the site of infection; subsequently, activated CD4(+) T cells producing IFN-gamma were primarily found. As protection correlated with the ratio of total IFN-gamma-producing cells (CD4(+) and CD8(+) T cells) to macrophages found at the site of infection, a role for IFN-gamma was evident; in addition, vaccination of IFN-gamma-deficient mice failed to provide protection. To further assess the effector mechanisms that mediate protection, mice deficient in perforin synthesis were examined. Perforin-deficient mice vaccinated with the P-8 antigen were unable to control infection. Thus, the elicitation of CD8(+) T cell effector mechanisms (perforin, IFN-gamma) are clearly required in the protective immune response against L. amazonensis infection in vaccinated mice.

Hemophagocytic lymphohistiocytosis is associated with deficiencies of cellular cytolysis but normal expression of transcripts relevant to killer-cell-induced apoptosis

In 65 patients with hemophagocytic lymphohistiocytosis (HLH), we found an as yet undescribed heterogeneity of defects in cellular cytotoxicity when assay conditions were modified by the incubation time, the presence of mitogen, or interleukin-2 (IL-2). The standard 4-hour natural killer (NK) test against K562 targets was negative in all patients. In patients deficient in type 1 (n = 21), type 2 (n = 5), and type 4 (n = 8) HLH, negative NK function could be reconstituted by mitogen, by IL-2, or by prolongation of the incubation time (16 hours), respectively. Most patients (n = 31) displayed the type 3 defect, defined by a lack of any cellular cytotoxicity independent of assay variations. The characteristic hypercytokinemia also concerned counterregulatory cytokines, such as proinflammatory interferon-gamma (IFN-gamma), simultaneously elevated with suppressive IL-10 in 38% of types 1-, 2-, and 4-deficient patients and in 71% of type 3-deficient patients. Elevated IFN-gamma alone correlated with high liver enzymes, but sCD95-ligand and sCD25 did not-though these markers were expected to indicate the extent of histiocytic organ infiltration. Outcome analysis revealed more deaths in patients with type 3 deficiency (P =.017). Molecular defects were associated with homozygously mutated perforin only in 4 patients, but other type 3 patients expressed normal transcripts of effector molecules for target-cell apoptosis, including perforin and granzyme family members, as demonstrated by RNase protection analysis. Thus, target-cell recognition or differentiation defects are likely to explain this severe phenotype in HLH. Hyperactive phagocytes combined with NK defects may imply defects on the level of the antigen-presenting cell.

Peripheral blood and granuloma CD4(+)CD28(-) T cells are a major source of interferon-gamma and tumor necrosis factor-alpha in Wegener's granulomatosis

To elucidate whether the fraction of CD28(-) T cells within the CD4(+) T-cell population is a major source of Th1-like and proinflammatory cytokine production driving Wegener's granulomatosis (WG) granuloma formation, we analyzed the phenotype and functional characteristics of peripheral blood CD4(+)CD28(-) T cells and of T cells in granulomatous lesions of 12 patients with active WG. Surface markers and intracytoplasmic cytokine and perforin expression were assessed by flow cytometry. Cytokine secretion was measured by enzyme-linked immunosorbent assay. Immunohistological studies demonstrated interferon-gamma and tumor necrosis factor-alpha cytokine positivity attributable to CD4(+)CD28(-) T cells in granulomatous lesions. Peripheral blood CD4(+)CD28(-) T cells expressed CD57, also found on natural killer cells, and intracytoplasmic perforin. They were generally CD25 (interleukin-2 receptor)-negative. CD18 (adhesion molecule beta(2)-integrin) was strongly up-regulated on CD4(+)CD28(-) T cells, whereas only a minority of CD4(+)CD28(+) T cells expressed CD18. CD4(+)CD28(-) T cells appeared as a major source of interferon-gamma and tumor necrosis factor-alpha. In contrast, CD4(+)CD28(+) T cells were able to produce and secrete a wider variety of cytokines including interleukin-2. One-quarter of CD4(+)CD28(+) T cells expressed the activation marker CD25, but they lacked perforin. Thus, CD4(+)CD28(-) T cells appeared more differentiated than CD4(+)CD28(+) T cells. They displayed Th1-like cytokine production and features suggestive of the capability of CD4(+) T-cell-mediated cytotoxicity. CD4(+)CD28(-) T cells may be recruited into granulomatous lesions from the blood via CD18 interaction, and may subsequently promote monocyte accumulation and granuloma formation through their cytokine secretion in WG.

Cytolytic pathways in haematopoietic stem-cell transplantation

The remarkable activity of donor T cells against malignant cells in the context of an allogeneic haematopoietic stem-cell transplantation (HSCT) is arguably, at present, the most potent clinical immunotherapy for cancer. However, alloreactive donor T cells are also important effector cells in the development of graft-versus-host disease (GVHD), which is a potentially lethal complication for recipients of an allogeneic HSCT. Therefore, the separation of the GVHD and graft-versus-tumour (GVT) activity of donor T cells has become a topic of great interest for many investigators. Recent studies have shown that donor T cells make differential use of their cytolytic pathways in mediating GVHD and GVT effects. Therefore, the selective blockade or enhancement of cytolytic pathways provides an intriguing therapeutic opportunity to separate the desired GVT effect from the potentially devastating GVHD.

The relationship of natural killer cell counts, perforin mRNA and CD2 expression to post-exercise natural killer cell activity in humans

The aim of this study was to further investigate the mechanism of suppression of natural killer (NK) cell cytotoxic activity in peripheral blood following strenuous exercise. Blood was collected for analysis of NK cell concentration, cytotoxic activity, CD2 surface expression and perforin gene expression from runners (RUN, n=6) and resting controls (CONTROL, n=4) pre-exercise, 0, 1.5, 5, and 24 h following a 60-min treadmill run at 80% of VO2 peak. Natural killer cytotoxic activity, measured using a whole blood chromium release assay, fluctuated minimally in the CONTROL group and increased by 63% and decreased by 43% 0 and 1.5 h post-exercise, respectively, in the RUN group (group x time, P < 0.001). Lytic index (cytotoxic activity per cell) did not change. Perforin mRNA, measured using quantitative real-time polymerase chain reaction (QRT-PCR) decreased from pre- to post-exercise and remained decreased through 24 h. The decrease from pre- to 0 h post-exercise was seen predominately in the RUN group and was inversely correlated (r=- 0.95) to pre-exercise perforin mRNA. The NK cell surface expression of CD2 (lymphocyte function-associated antigen-2) was determined using fluorescent antibodies and flow cytometry. There was no change in the proportion of NK cells expressing CD2 or CD2 density. We conclude that (1) numerical redistribution accounted for most of the change in NK cytotoxic activity following a strenuous run, (2) decrease in perforin gene expression during the run was inversely related to pre-exercise levels but did not parallel changes in cytotoxic activity, and (3) CD2 surface expression was not affected by exercise.

Channel formation by serum amyloid A: a potential mechanism for amyloid pathogenesis and host defense

Serum amyloid A (SAA) is a family of closely related apolipoproteins associated with high density lipoprotein (HDL). Subclasses of SAA isoforms are differentially expressed constitutively and during inflammation. During states of infection or inflammation, levels of HDL bound, acute phase isoforms of SAA rise as much as 1000-fold in the serum, suggesting that it might play a role in host defense. Following recurrent or chronic inflammation, an N-terminal peptide fragment of SAA known as amyloid A (AA) assembles into fibrils causing extensive damage to spleen, liver, and kidney, and rapidly progressing to death. In the present paper, we report the novel finding that a recombinant acute phase isoform variant of human SAA 1.1 (SAAp) readily forms ion-channels in planar lipid bilayer membranes at physiologic concentrations. These channels are voltage-independent, poorly selective, and are relatively long-lived This type of channel would place a severe metabolic strain on various kinds of cells. Expression of human SAA 1.1 in bacteria induces lysis of bacterial cells, while expression of the constitutive isoform (human SAA4) does not. Secondary structural analysis of the SAA isoforms in dicates a strong hydrophobicity of the N-terminal of the acute phase isoform relative to the constitutive SAA4 isoform, which may be responsible for the bactericidal activity of the former, in keeping with the notion that SAA 1 targets cell membranes and forms channels in them. Channel formation may thus be related to a host defense role of acute phase SAA isoforms and may also be the mechanism of end organ damage in AA and other amyloidoses.

Structural dynamics of oligodendrocyte lysis by perforin in culture: relevance to multiple sclerosis

The mechanism by which oligodendrocytes are depleted from active lesions in multiple sclerosis (MS) is not clear but many reports implicate a cytolytic process. The most applied animal model for MS, chronic relapsing experimental autoimmune encephalomyelitis (EAE), has been established in inbred strains of mice, especially SJL and PL. Studies on oligodendrocytes from these strains in vitro have been hampered to date by an inability to grow these cells from mouse CNS tissue. We report here a successful method to culture SJL mouse oligodendrocytes and have analyzed lysis of these cells in vitro mediated by the pore-forming protein, perforin, a candidate effector molecule in inflammatory demyelination. Cultures were exposed to murine perforin, 36-72 hemolytic U, for up to 2.5 hr and examined using the oligodendrocyte phenotypic markers O4, galactocerebroside and myelin basic protein (MBP), in addition to a membrane dye (DiI) and a marker of necrosis, propidium iodide, (PI). Cultures were imaged chronologically by phase contrast, immunofluorescence, digital, light and electron microscopy. Findings showed that the majority of oligodendrocytes were killed within 60-90 min via pore expansion and ultimately, membrane disruption. The structural features of the cellular damage comprised swelling of the cell body, fenestration and fragmentation of membranes and processes, cytoplasmic vacuolation and breakdown of the nuclear envelope. Astrocytes in the same system were relatively resistant to cell lysis. The above patterns of oligodendrocyte damage in SJL oligodendrocytes were reminiscent of patterns in the MS lesion, leaving us to conclude that perforin may play an important role in the human disease.

Granzymes: a family of lymphocyte granule serine proteases

SUMMARY

Granzymes, a family of serine proteases, are expressed exclusively by cytotoxic T lymphocytes and natural killer (NK) cells, components of the immune system that protect higher organisms against viral infection and cellular transformation. Following receptor-mediated conjugate formation between a granzyme-containing cell and an infected or transformed target cell, granzymes enter the target cell via endocytosis and induce apoptosis. Granzyme B is the most powerful pro-apoptotic member of the granzyme family. Like caspases, cysteine proteases that play an important role in apoptosis, it can cleave proteins after acidic residues, especially aspartic acid. Other granzymes may serve additional functions, and some may not induce apoptosis. Granzymes have been well characterized only in human and rodents, and can be grouped into three subfamilies according to substrate specificity: members of the granzyme family that have enzymatic activity similar to the serine protease chymotrypsin are encoded by a gene cluster termed the 'chymase locus'; granzymes with trypsin-like specificities are encoded by the 'tryptase locus'; and a third subfamily cleaves after unbranched hydrophobic residues, especially methionine, and is encoded by the 'Met-ase locus'. All granzymes are synthesized as zymogens and, after clipping of the leader peptide, maximal enzymatic activity is achieved by removal of an amino-terminal dipeptide. They can all be blocked by serine protease inhibitors, and a new group of inhibitors has recently been identified - serpins, some of which are specific for granzymes. Future studies of serpins may bring insights into how cells that synthesize granzymes are protected from inadvertent cell suicide.

Participation of innate and acquired immunity in atherosclerosis

Coronary artery disease, the major manifestation of atherosclerosis, is the leading cause of death in the Western world. However, the pathogenesis of atherosclerosis is still poorly understood. Controversy exists regarding the participation of innate immunity involving macrophages and natural killer (NK) cells vs antigen-specific acquired immunity involving lymphocytes. Macrophages predominate in atherosclerotic lesions. NK cells, although smaller in number, are present as well. Furthermore, T lymphocytes that participate in acquired immunity are frequently observed in lesions and can modulate lesion progression. By using mouse models of hyperlipidemia, our laboratory is addressing in vivo the participation of both innate inflammatory responses and acquired immune responses in atherosclerosis.

Interferon-γ–induced membrane PAF-receptor expression confers tumor cell susceptibility to NK perforin-dependent lysis

Perforin is known to display a membranolytic activity on tumor cells. Nevertheless, perforin release during natural killer (NK)–cell activation is not sufficient to induce membrane target-cell damage. On the basis of the ability of perforin to interact with phospholipids containing a choline phosphate headgroup, we identify the platelet-activating factor (PAF) and its membrane receptor as crucial components in tumor cell killing activity of human resting NK cells. We demonstrate for the first time that upon activation, naive NK cells release the choline phosphate–containing lysolipid PAF, which binds to perforin and acts as an agonist on perforin-induced membrane damage. PAF is known to incorporate cell membranes using a specific receptor. Here we show that interferon-γ (IFN–γ) secreted from activated NK cells ends in PAF-receptor expression on perforin-sensitive K562 cells but not on perforin-resistant Daudi cells. In order to prove the capacity of PAF to interact simultaneously with its membrane PAF receptor and with perforin, we successfully co-purified the 3 components in the presence of bridging PAF molecules. The functional activity of this complex was further examined. The aim was to determine whether membrane PAF-receptor expression on tumor cells, driven to express this receptor, could render them sensitive to the perforin lytic pathway. The results confirmed that transfection of the PAF-receptor complementary DNA into major histocompatibility complex class I and Fas-receptor negative tumor cells restored susceptibility to naive NK cells and perforin attack. Failure of IFN-γ to induce membrane PAF receptor constitutes the first described mechanism for tumor cells to resist the perforin lytic pathway.

Interferon-γ–induced membrane PAF-receptor expression confers tumor cell susceptibility to NK perforin-dependent lysis

Perforin is known to display a membranolytic activity on tumor cells. Nevertheless, perforin release during natural killer (NK)–cell activation is not sufficient to induce membrane target-cell damage. On the basis of the ability of perforin to interact with phospholipids containing a choline phosphate headgroup, we identify the platelet-activating factor (PAF) and its membrane receptor as crucial components in tumor cell killing activity of human resting NK cells. We demonstrate for the first time that upon activation, naive NK cells release the choline phosphate–containing lysolipid PAF, which binds to perforin and acts as an agonist on perforin-induced membrane damage. PAF is known to incorporate cell membranes using a specific receptor. Here we show that interferon-γ (IFN–γ) secreted from activated NK cells ends in PAF-receptor expression on perforin-sensitive K562 cells but not on perforin-resistant Daudi cells. In order to prove the capacity of PAF to interact simultaneously with its membrane PAF receptor and with perforin, we successfully co-purified the 3 components in the presence of bridging PAF molecules. The functional activity of this complex was further examined. The aim was to determine whether membrane PAF-receptor expression on tumor cells, driven to express this receptor, could render them sensitive to the perforin lytic pathway. The results confirmed that transfection of the PAF-receptor complementary DNA into major histocompatibility complex class I and Fas-receptor negative tumor cells restored susceptibility to naive NK cells and perforin attack. Failure of IFN-γ to induce membrane PAF receptor constitutes the first described mechanism for tumor cells to resist the perforin lytic pathway.

Novel therapy for COPD

The incidence of chronic obstructive pulmonary disease (COPD) is increasing throughout the world. Much less is known about the pathogenesis of COPD than that of asthma and there is little response to current therapy. Most patients with COPD have acquired their lung disease through smoking cigarettes, and the major step in management is to minimise further damage by stopping this habit. A number of therapies are being developed for the treatment of COPD; including new bronchodilators such as tiotropium bromide, agents to block inflammation induced by neutrophils and macrophages, as well as strategies to combat proteases and oxidants. The long-term goal is to provide therapy that retards the accelerated loss of lung function occurring in COPD. Development of novel therapies for COPD requires reliable Phase II decision making before entering large scale Phase III studies. The patient with COPD is often overlooked compared to their asthmatic counterpart, who benefit from an urgent need to identify novel targets and better therapy.

Preferential Localization of CD8+ αEβ7+ T Cells Around Acinar Epithelial Cells with Apoptosis in Patients with Sjögren’s Syndrome

The T lymphocytes that infiltrate the exocrine glands in Sjögren’s syndrome (SS) play a key role in damaging glandular epithelial cells, but the mechanisms of this damage by T lymphocytes are not fully understood. To determine the cellular basis of this phenomenon, we focused our attention on the T lymphocytes around acinar epithelial cells in SS. We showed that CD8+ but not CD4+ T lymphocytes were located around the acinar epithelial cells and that a majority of these CD8+ T lymphocytes possess an unique integrin, αEβ7 (CD103). The acinar epithelial cell adherent with αEβ7 (CD103)+ CD8+ T lymphocytes was apoptotic. Both the perforin/granzyme B and Fas/Fas ligand pathways were implicated in the process of programmed cell death in lacrimal glands. These results suggested that αEβ7 integrin, by interacting with E-cadherin, mediates the adhesion between CD8+ T lymphocytes and acinar epithelial cells in SS and participates in inducing epithelial cell apoptosis, leading to secretory dysfunction of exocrine glands, a hallmark of SS.

Perforin-dependent nuclear targeting of granzymes: A central role in the nuclear events of granule-exocytosis-mediated apoptosis?

Programmed cell death, apoptosis, involves very distinctive changes within the target cell nucleus, including margination of the chromatin, DNA fragmentation and breakdown of the nuclear envelope. Cytolytic granule-mediated target cell apoptosis is effected, in part, through synergistic action of the membrane-acting protein perforin and serine proteases, such as granzymes A or B. Recent work using confocal laser scanning microscopy as well as other techniques supports the idea that perforin-dependent translocation of granzymes to the nucleus of target cells plays a central role in effecting the nuclear changes associated with apoptosis. In vitro experiments indicate that granzyme nuclear import follows a novel pathway, being independent of ATP, not inhibitable by non-hydrolysable GTP analogues and involving binding within the nucleus, unlike conventional signal- dependent nuclear protein import. In intact cells, perforin-dependent nuclear entry of granzymes precedes the nuclear events of apoptosis such as DNA fragmentation and nuclear envelope breakdown; prevention of granzyme nuclear translocation through bcl2 overexpression or treatment of target cells with inhibitors of caspase activation blocks these events. Nuclear localization of granzymes thus appears to be central to induction of the nuclear changes associated with cytolytic granule-mediated apoptosis.

Redirecting Effector T Cells Through Their IL-2 Receptors

Fusion proteins constructed of a tumor-specific Ab joined to IL-2 (Ab-IL-2) have been used in the past to deliver cytokine directly to the site of tumor cells in vivo. These molecules mimic the activity of IL-2 and assist in activating and expanding antitumor effector cells. To enhance the cytolytic activity of CTL specific for peptide epitopes of the Her-2/neu tumor Ag presented by HLA-A*0201 molecules, a fusion protein was constructed consisting of a single chain Ab specific for Her-2/neu, linked to IL-2 (neu-Ab-IL-2). When added to a mixture of tumor cells and Her-2/neu-specific CTL, the protein was found to augment lysis of tumor cells. In addition, the hybrid molecule also promoted lysis of Her-2/neu expressing tumors by non-tumor-specific cloned T cell lines, including Th1 CD4 cells. Analysis of the mechanism of cytotoxicity revealed that the fusion protein mediates the formation of stable conjugates between T cells expressing IL-2R and tumor cells expressing Her-2/neu, resulting in lysis through the Fas-Fas ligand pathway. Lysis induction was independent of specific engagement by the TCR. When tested for its ability to enhance tumor cell eradication by Her-2/neu-specific CD8+ T cells in an adoptive transfer model in SCID mice, neu-Ab-IL-2 facilitated the elimination of tumor cells in vivo. Surprisingly, the combination of non-tumor-specific CD8+ T cells and fusion protein also induced a significant delay of tumor growth. This represents a novel approach for redirecting non-tumor-specific T cells to eliminate tumors.

Functional subsets of CD4 T cells in rheumatoid synovitis

OBJECTIVE

To identify the functional properties of CD4+ CD28- T cells, which accumulate and clonally expand in patients with rheumatoid arthritis (RA).

METHODS

The gene expression of molecules involved in T cell effector functions was compared in CD4+ CD28- and CD4+ CD28+ T cell clones. The expression of differentially up-regulated genes was confirmed by flow cytometry of T cells and by 2-color immunohistochemistry of rheumatoid synovial tissue. Cytotoxicity of CD4+ CD28- T cells was tested by anti-CD3 redirected lysis of Fc receptor-positive target cells.

RESULTS

CD4+ CD28- T cell clones lacked messenger RNA for the CD40 ligand (CD40L) but transcribed the perforin gene. Perforin was also found in freshly isolated CD4+ CD28- peripheral blood lymphocytes from RA patients. CD4+ CD28-, but not CD4+ CD28+, T cell clones lysed Fc receptor-bearing target cells. CD4+ perforin-positive T cells were present in the synovial tissue, where their frequency correlated with the expansion of the CD4+ CD28- compartment in the periphery. Among tissue-infiltrating CD4+ T cells, only the CD40L-negative subset expressed perforin transcripts.

CONCLUSION

Clonally expanded CD4+ CD28- T cells are functionally specialized for killing, while they lack the ability to provide B cell help. Tissue-infiltrating CD4+ T cells can be subdivided phenotypically and functionally into at least 2 distinct subsets based on their expression of perforin and CD40L. Because the expansion of CD4+ CD28- T cells is associated with extraarticular RA, T cell-mediated cytotoxicity may be particularly important in these most severe complications of RA.

Application of membrane-active peptides for drug and gene delivery across cellular membranes

Naturally occurring peptides and protein domains with amphipathic sequences play a dominant role in physiological, lipid membrane-reorganizing processes like fusion, disruption, or pore formation. More recently this capacity to modulate membrane integrity has been exploited for drug delivery into cells. Incorporation of synthetic membrane-active peptides into delivery systems has been found to enhance intracellular delivery of drugs including oligonucleotides, peptides, or plasmid DNA. In the majority of applications, the amphipathic peptides are designed to act after uptake by endocytosis, releasing the delivered agent from intracellular vesicles to the cytoplasm. Alternatively, peptides might mediate direct drug transfer across the plasma membrane. Although encouraging results have been obtained with the use of synthetic peptides to enhance cellular delivery of various compounds, the naturally evolved mechanisms observed in the entry of viruses or protein toxins are still far more efficient. For the development of improved synthetic peptides and carrier systems a better understanding of the molecular details of membrane-destabilization and reorganization will be essential.

Direct visualization of antigen-specific CD8+ T cells during the primary immune response to Epstein-Barr virus In vivo

Primary infection with virus can stimulate a vigorous cytotoxic T cell response. The magnitude of the antigen-specific component versus the bystander component of a primary T cell response remains controversial. In this study, we have used tetrameric major histocompatibility complex-peptide complexes to directly visualize antigen-specific cluster of differentration (CD)8+ T cells during the primary immune response to Epstein-Barr virus (EBV) infection in humans. We show that massive expansion of activated, antigen-specific T cells occurs during the primary response to this virus. In one individual, T cells specific for a single EBV epitope comprised 44% of the total CD8+ T cells within peripheral blood. The majority of the antigen-specific cells had an activated/memory phenotype, with expression of human histocompatibility leukocyte antigen (HLA) DR, CD38, and CD45RO, downregulation of CD62 leukocyte (CD62L), and low levels of expression of CD45RA. After recovery from AIM, the frequency of antigen-specific T cells fell in most donors studied, although populations of antigen-specific cells continued to be easily detectable for at least 3 yr.