Decoding NADPH oxidase 4 expression in human tumors

NADPH oxidase 4 (NOX4) is a redox active, membrane-associated protein that contributes to genomic instability, redox signaling, and radiation sensitivity in human cancers based on its capacity to generate H₂O₂ constitutively. Most studies of NOX4 in malignancy have focused on the evaluation of a small number of tumor cell lines and not on human tumor specimens themselves; furthermore, these studies have often employed immunological tools that have not been well characterized. To determine the prevalence of NOX4 expression across a broad range of solid tumors, we developed a novel monoclonal antibody that recognizes a specific extracellular region of the human NOX4 protein, and that does not cross-react with any of the other six members of the NOX gene family. Evaluation of 20 sets of epithelial tumors revealed, for the first time, high levels of NOX4 expression in carcinomas of the head and neck (15/19 patients), esophagus (12/18 patients), bladder (10/19 patients), ovary (6/17 patients), and prostate (7/19 patients), as well as malignant melanoma (7/15 patients) when these tumors were compared to histologically-uninvolved specimens from the same organs. Detection of NOX4 protein upregulation by low levels of TGF-β1 demonstrated the sensitivity of this new probe; and immunofluorescence experiments found that high levels of endogenous NOX4 expression in ovarian cancer cells were only demonstrable associated with perinuclear membranes. These studies suggest that NOX4 expression is upregulated, compared to normal tissues, in a well-defined, and specific group of human carcinomas, and that its expression is localized on intracellular membranes in a fashion that could modulate oxidative DNA damage.

Depletion of oxaloacetate decarboxylase FAHD1 inhibits mitochondrial electron transport and induces cellular senescence in human endothelial cells

In this study we report the identification of FAH domain containing protein 1 (FAHD1), a recently described member of the fumarylacetoacetate hydrolase (FAH) superfamily of metabolic enzymes, as a novel player in the regulation of cellular senescence. FAHD1 was found in a proteomic screen searching for mitochondrial proteins, which are differentially regulated in mitochondria from young and senescent human endothelial cells, and subsequently identified as oxaloacetate decarboxylase. We report here that depletion of FAHD1 from human endothelial cells inhibited mitochondrial energy metabolism and subsequently induced premature senescence. Whereas senescence induced by FAHD1 depletion was not associated with DNA damage, we noted a reduction of mitochondrial ATP-coupled respiration associated with upregulation of the cdk inhibitor p21. These results indicate that FAHD1 is required for mitochondrial function in human cells and provide additional support to the growing evidence that mitochondrial dysfunction can induce cellular senescence by metabolic alterations independent of the DNA damage response pathway.

A monoclonal antibody raised against bacterially expressed MPV17 sequences shows peroxisomal, endosomal and lysosomal localisation in U2OS cells

Recessive mutations in the MPV17 gene cause mitochondrial DNA depletion syndrome, a fatal infantile genetic liver disease in humans. Loss of function in mice leads to glomerulosclerosis and sensineural deafness accompanied with mitochondrial DNA depletion. Mutations in the yeast homolog Sym1, and in the zebra fish homolog tra cause interesting, but not obviously related phenotypes, although the human gene can complement the yeast Sym1 mutation. The MPV17 protein is a hydrophobic membrane protein of 176 amino acids and unknown function. Initially localised in murine peroxisomes, it was later reported to be a mitochondrial inner membrane protein in humans and in yeast. To resolve this contradiction we tested two new mouse monoclonal antibodies directed against the human MPV17 protein in Western blots and immunohistochemistry on human U2OS cells. One of these monoclonal antibodies showed specific reactivity to a protein of 20 kD absent in MPV17 negative mouse cells. Immunofluorescence studies revealed colocalisation with peroxisomal, endosomal and lysosomal markers, but not with mitochondria. This data reveal a novel connection between a possible peroxisomal/endosomal/lysosomal function and mitochondrial DNA depletion.

FAH domain containing protein 1 (FAHD-1) is required for mitochondrial function and locomotion activity in C. elegans

The fumarylacetoacetate hydrolase (FAH) protein superfamily of metabolic enzymes comprises a diverse set of enzymatic functions, including ß-diketone hydrolases, decarboxylases, and isomerases. Of note, the FAH superfamily includes many prokaryotic members with very distinct functions that lack homologs in eukaryotes. A prokaryotic member of the FAH superfamily, referred to as Cg1458, was shown to encode a soluble oxaloacetate decarboxylase (ODx). Based on sequence homologies to Cg1458, we recently identified human FAH domain containing protein-1 (FAHD1) as the first eukaryotic oxaloacetate decarboxylase. The physiological functions of ODx in eukaryotes remain unclear. Here we have probed the function of fahd-1, the nematode homolog of FAHD1, in the context of an intact organism. We found that mutation of fahd-1 resulted in reduced brood size, a deregulation of the egg laying process and a severe locomotion deficit, characterized by a reduced frequency of body bends, reduced exploratory movements and reduced performance in an endurance exercise test. Notably, mitochondrial function was altered in the fahd-1(tm5005) mutant strain, as shown by a reduction of mitochondrial membrane potential and a reduced oxygen consumption of fahd-1(tm5005) animals. Mitochondrial dysfunction was accompanied by lifespan extension in worms grown at elevated temperature; however, unlike in mutant worms with a defect in the electron transport chain, the mitochondrial unfolded protein response was not upregulated in worms upon inactivation of fahd-1. Together these data establish a role of fahd-1 to maintain mitochondrial function and consequently physical activity in nematodes.

Identification of FAH domain-containing protein 1 (FAHD1) as oxaloacetate decarboxylase

Fumarylacetoacetate hydrolase (FAH) domain-containing proteins occur in both prokaryotes and eukaryotes, where they carry out diverse enzymatic reactions, probably related to structural differences in their respective FAH domains; however, the precise relationship between structure of the FAH domain and the associated enzyme function remains elusive. In mammals, three FAH domain-containing proteins, FAHD1, FAHD2A, and FAHD2B, are known; however, their enzymatic function, if any, remains to be demonstrated. In bacteria, oxaloacetate is subject to enzymatic decarboxylation; however, oxaloacetate decarboxylases (ODx) were so far not identified in eukaryotes. Based on molecular modeling and subsequent biochemical investigations, we identified FAHD1 as a eukaryotic ODx enzyme. The results presented here indicate that dedicated oxaloacetate decarboxylases exist in eukaryotes.

ROS signaling by NADPH oxidase 5 modulates the proliferation and survival of prostate carcinoma cells

Prostate cancer (PCa) is the most commonly diagnosed cancer and second leading cause of male cancer death in Western nations. Thus, new treatment modalities are urgently needed. Elevated production of reactive oxygen species (ROS) by NADPH oxidase (Nox) enzymes is implicated in tumorigenesis of the prostate and other tissues. However, the identity of the Nox enzyme(s) involved in prostate carcinogenesis remains largely unknown. Analysis of radical prostatectomy tissue samples and benign and malignant prostate epithelial cell lines identified Nox5 as an abundantly expressed Nox isoform. Consistently, immunohistochemical staining of a human PCa tissue microarray revealed distinct Nox5 expression in epithelial cells of benign and malignant prostatic glands. shRNA‐mediated knockdown of Nox5 impaired proliferation of Nox5‐expressing (PC‐3, LNCaP) but not Nox5‐negative (DU145) PCa cell lines. Similar effects were observed upon ROS ablation via the antioxidant N‐acetylcysteine confirming ROS as the mediators. In addition, Nox5 silencing increased apoptosis of PC‐3 cells. Concomitantly, protein kinase C zeta (PKCζ) protein levels and c‐Jun N‐terminal kinase (JNK) phosphorylation were reduced. Moreover, the effect of Nox5 knockdown on PC‐3 cell proliferation could be mimicked by pharmacological inhibition of JNK. Collectively, these data indicate that Nox5 is expressed at functionally relevant levels in the human prostate and clinical PCa. Moreover, findings herein suggest that Nox5‐derived ROS and subsequent depletion of PKCζ and JNK inactivation play a critical role in modulating intracellular signaling cascades involved in the proliferation and survival of PCa cells. © 2014 The Authors. Molecular Carcinogenesis published by Wiley Periodicals, Inc.

Characterisation of Nox4 inhibitors from edible plants

NADPH oxidases transport electrons from cytosolic NADPH through biological membranes to generate reactive oxygen species. NADPH oxidase 4, broadly expressed in humans, is an interesting pharmacological target, since its activity is deregulated in several diseases, including pulmonary fibrosis, diabetic nephropathy, and cardiac hypertrophy. Whereas several candidate NADPH oxidase 4 inhibitors were recently described, most of these compounds are either unspecific or toxic. Here we set out to identify new NADPH oxidase 4 inhibitors from edible plants, in an attempt to decrease the number of hits with toxic side effects. We screened a compound library prepared from edible plants for new bioactives with the ability to inhibit the activity of NADPH oxidase 4. Using both cell-based and cell-free assays, we identified several compounds with significant inhibitory activity towards NADPH oxidase 4. For selected compounds, the activity profile towards NADPH oxidase 2 and NADPH oxidase 5 was established, and controls were carried out to exclude general reactive oxygen species scavengers. A number of promising NADPH oxidase 4 inhibitors from edible plants was identified and characterised. Several new chemical entities are disclosed which act as NADPH oxidase 4 inhibitors, and the efficacies of our best hits, in particular several diarylheptanoids and lignans, are comparable to the best available pharmacological NADPH oxidase 4 inhibitors. These findings will provide valuable tools to study mechanisms of NADPH oxidase inhibition.

Identification of human fumarylacetoacetate hydrolase domain-containing protein 1 (FAHD1) as a novel mitochondrial acylpyruvase

The human fumarylacetoacetate hydrolase (FAH) domain-containing protein 1 (FAHD1) is part of the FAH protein superfamily, but its enzymatic function is unknown. In the quest for a putative enzymatic function of FAHD1, we found that FAHD1 exhibits acylpyruvase activity, demonstrated by the hydrolysis of acetylpyruvate and fumarylpyruvate in vitro, whereas several structurally related compounds were not hydrolyzed as efficiently. Conserved amino acids Asp-102 and Arg-106 of FAHD1 were found important for its catalytic activity, and Mg(2+) was required for maximal enzyme activity. FAHD1 was found expressed in all tested murine tissues, with highest expression in liver and kidney. FAHD1 was also found in several human cell lines, where it localized to mitochondria. In summary, the current work identified mammalian FAHD1 as a novel mitochondrial enzyme with acylpyruvate hydrolase activity.

Analysis of the cellular uptake and nuclear delivery of insulin-like growth factor binding protein-3 in human osteosarcoma cells

Insulin-like growth factor (IGF) binding protein-3 (IGFBP-3) regulates cell proliferation and survival by extracellular interaction and inactivation of the growth factor IGF-I. Beyond that, IGF-independent actions mediated by intracellular IGFBP-3 including nuclear-IGFBP-3, have also been described. We here show, using both confocal and electron microscopy and cell fractionation, that the extracellular addition of IGFBP-3 to living cells results in rapid uptake and nuclear delivery of IGFBP-3, by yet partly unknown mechanisms. IGFBP-3 is internalized through a dynamin-dependent pathway, traffics through endocytic compartments and is finally delivered into the nucleus. We observed docking of IGFBP-3 containing structures to the nuclear envelope and found IGFBP-3 containing dot-like structures to permeate the nuclear envelope. In summary, our findings establish the pathway by which this tumor suppressor protein is delivered from extracellular space to the nucleus.

Subcellular localization of the human papillomavirus 16 E7 oncoprotein in CaSki cells and its detection in cervical adenocarcinoma and adenocarcinoma in situ

E7 is the major oncoprotein of high-risk human papillomaviruses (HPV) which causes cervical cancer. To date E7 oncoproteins have not been investigated in cervical adenocarcinoma. In this study we generated a rabbit monoclonal anti-HPV-16 E7 antibody, RabMab42-3, which recognizes a conformational epitope in the E7 carboxy-terminal zinc-finger resulting in a strong increase in the sensitivity for the detection of cell-associated HPV-16 E7 protein relative to conventional polyclonal anti-HPV-16 E7 antibodies. Using RabMab42-3, we show that the subcellular localization of endogenous HPV-16 E7 oncoprotein varies during the cell cycle in cervical cancer cells. Moreover, we demonstrate for the first time that the HPV-16 E7 oncoprotein is abundantly expressed in cervical adenocarcinoma in situ and adenocarcinoma, suggesting an important role of HPV-16 E7 for the development of these tumors. Our findings suggest that the HPV-16 E7 oncoprotein could be a useful marker for the detection of cervical adenocarcinoma and their precursors.

Novel mechanism of IGF-binding protein-3 action on prostate cancer cells: inhibition of proliferation, adhesion, and motility

IGF-binding protein-3 (IGFBP-3) is a modulator of the IGF-signaling pathway and was described as an anti-cancer agent in prostate cancer. The molecular mechanisms underlying these effects remained, however, largely undefined. We analyzed the influence of recombinant IGFBP-3 on cell proliferation of PC3, Du145, and LNCaP prostate cancer cells. As expected, IGFBP-3 inhibited IGF-stimulated cell proliferation by blocking IGF-mediated proliferation signals, but we observed an IGF-independent inhibitory effect of IGFBP-3 on prostate cancer cell proliferation in long-term cultures. We further investigated the influence of IGFBP-3 on adhesion, motility, and invasion of prostate cancer cells using adhesion assays, live-cell imaging techniques, and matrigel invasion measurements. There was a clear inhibitory effect of IGFBP-3 on tumor cell adhesion to extracellular matrix components in the presence and absence of IGF, whereas cell-cell adhesion was not affected. The same inhibitory effect of IGFBP-3 was determined on cell motility when real-time cell movements were followed. In addition, IGFBP-3 was able to inhibit tumor cell invasion through matrigel. In summary, we show that IGFBP-3 inhibits proliferation, adhesion, migration, and invasion processes of prostate tumor cells. These newly described mechanisms of IGFBP-3 can be of importance for tumor progression and support a role of IGFBP-3 in therapeutic settings.

High-risk human papillomavirus E7 oncoprotein detection in cervical squamous cell carcinoma

PURPOSE

Persistent infections by high-risk human papillomavirus (HPV) types are the main etiologic factor for cervical cancer. The objective of this study was to evaluate whether high-risk E7 oncoprotein is adequate as a marker for the detection of cervical cancer.

EXPERIMENTAL DESIGN

HPV typing was done in biopsies from 58 cervical carcinoma and 22 normal cervical squamous epithelia. The HPV-16 E7, HPV-18 E7, and HPV-45 E7 oncoprotein levels were monitored by immunohistochemistry and compared with those of p16(INK4a) and Ki67.

RESULTS

Fifty-five (94.8%) tumors were high-risk HPV-DNA-positive (46 HPV-16, 2 HPV-16 and HPV-18, 4 HPV-18, 1 HPV-33, and 2 HPV-45). HPV-DNA could not be detected in three tumors (5.2%). High HPV E7 oncoprotein levels were shown in 57 cervical cancers (98.3%), without correlation between expression levels and tumor stages.

CONCLUSION

This is the first study which systematically analyzes the levels of the major HPV oncoproteins in cervical carcinomas demonstrating that the high-risk HPV E7 proteins are regularly expressed in these cancers. This suggests that high-risk E7 oncoproteins are necessary for cervical cancers and apparently essential as tumor marker.

Viral infections induce abundant numbers of senescent CD8 T cells

Viral infections are often accompanied by extensive proliferation of reactive CD8 T cells. After a defined number of divisions, normal somatic cells enter a nonreplicative stage termed senescence. In the present study we have identified the inhibitory killer cell lectin-like receptor G1 (KLRG1) as a unique marker for replicative senescence of murine CD8 T cells. KLRG1 expression was induced in a substantial portion (30-60%) of CD8 T cells in C57BL/6 mice infected with lymphocytic choriomeningitis virus (LCMV), vesicular stomatitis virus, or vaccinia virus. Similarly, KLRG1 was found on a large fraction of LCMV gp33 peptide-specific TCR-transgenic (tg) effector and memory cells activated in vivo using an adoptive transfer model. Transfer experiments with CFSE-labeled TCR-tg cells into LCMV-infected hosts further indicated that induction of KLRG1 expression required an extensive number of cell divisions. Most importantly, KLRG1(+) TCR-tg effector/memory cells could efficiently lyse target cells and secrete cytokines, but were severely impaired in their ability to proliferate after Ag stimulation. Thus, this study demonstrates that senescent CD8 T cells are induced in abundant numbers during viral infections in vivo.

Concerted action of the FasL/Fas and perforin/granzyme A and B pathways is mandatory for the development of early viral hepatitis but not for recovery from viral infection

Cytotoxic T lymphocytes (CTL) play a major role in the recovery from primary viral infections and the accompanying tissue injuries. However, it is unclear to what extent the two main cytolytic pathways, perforin-granzyme A and B exocytosis and Fas ligand (FasL)-Fas interaction, contribute to these processes. Here we have employed mouse strains with either spontaneous mutations or targeted gene defects in one or more components of either of the two cytolytic pathways to analyze the molecular basis of viral clearance and induction of hepatitis during lymphocytic choriomeningitis virus infection. Our results reveal that viral clearance is solely dependent on perforin but that virus-induced liver damage only occurs when both the FasL/Fas and the perforin pathways, including granzymes A and B, are simultaneously activated. The finding that development of hepatitis but not viral clearance is dependent on the concomitant activation of FasL-Fas and perforin-granzymes may be helpful in designing novel strategies to prevent hepatic failures during viral infections.

Genomic structure, alternative splicing, and physical mapping of the killer cell lectin-like receptor G1 gene (KLRG1), the mouse homologue of MAFA

The mouse killer cell lectin-like receptor G1 (KLRG1), the mouse homologue of the mast cell function-associated antigen (MAFA), is an inhibitory C-type lectin expressed on natural killer (NK) cells and activated CD8 T cells. Here we report the complete nucleotide sequence, alternatively spliced variants, and the physical mapping of the KLRG1 gene in the mouse. The gene spans about 13 kb and consists of five exons. Short interspersed repeats of the B1 and B2 family, a LINE-1-like element, and a (CTT)170 triplet repeat were found in intron sequences. In contrast to human KLRG1 and to the murine KLR family members, mouse KLRG1 locates outside the NK complex on Chromosome 6 between the genes encoding CD9 and CD4.

Partial impairment of cytokine responses in Tyk2-deficient mice

To assess the role of the Janus kinase (Jak) family member Tyk2, we have generated Tyk2-/- mice. In contrast to other Jaks, where inactivation leads to a complete loss of the respective cytokine receptor signal, Tyk2-/- mice display reduced responses to IFNalpha/beta and IL-12 and a selective deficiency in Stat3 activation in these pathways. Unexpectedly, IFNgamma signaling is also impaired in Tyk2-/- mice. Tyk2-/- macrophages fail to produce nitric oxide upon lipopolysaccharide induction. Tyk2-/- mice are unable to clear vaccinia virus and show a reduced T cell response after LCMV challenge. These data imply a selective contribution of Tyk2 to the signals triggered by various biological stimuli and cytokine receptors.

Differential requirement of perforin and IFN-gamma in CD8 T cell-mediated immune responses against B16.F10 melanoma cells expressing a viral antigen

Perforin-mediated lysis and secretion of IFN-gamma belong to the key effector functions of CD8 T cells. To compare the anti-tumor activity of these two mechanisms, we used B16.F10 melanoma cells (B16GP33) expressing the cytotoxic T cell epitope GP33 and T cell receptor transgenic (TCR-tg) mice specific for GP33 and deficient in perforin or IFN-gamma. B16GP33 tumor cells, injected either i.v. to induce experimental metastases or s.c., were similarly controlled in both wild-type and perforin-deficient, but not in IFN-gamma-deficient TCR-tg mice. A similar result was obtained when the therapeutic efficacy of adoptively transferred TCR-tg effector cells from these mice was examined in the corresponding perforin- or IFN-gamma-deficient C57BL/6 hosts. Criss-cross experiments further revealed that IFN-gamma production by the host strongly influenced the efficiency of the adoptively transferred effector cells. In contrast to the potent ability of GP33-specific effector cells to mediate B16GP33 tumor regression without perforin, GP33-specific memory cells, induced with recombinant vaccinia virus expressing GP33, failed to control B16GP33 tumor growth in the absence of perforin. In conclusion, our data demonstrate a crucial role for IFN-gamma in B16GP33 tumor cell elimination in vivo and indicate a differential requirement of perforin by effector versus memory CD8 T cells in anti-tumor immunity.

Break of T cell ignorance to a viral antigen in the liver induces hepatitis

To study peripheral tolerance of CD8 T cells to a classically MHC-restricted peptide Ag expressed in hepatocytes, ALB1 transgenic (tg) mice expressing the CTL epitope GP33 of the lymphocytic choriomeningitis virus glycoprotein under control of the mouse albumin promoter were generated. ALB1 mice exclusively expressed the GP33 transgene in the liver and, at a 100- to 1000-fold lower level, in the thymus. TCR-tg mice specific for the GP33 epitope were used to directly follow GP33-specific T cells in vivo. These experiments revealed that 1) thymic expression of the GP33 transgene led to incomplete central deletion of TCR-tg cells; and 2) peripheral TCR-tg cells in ALB1 mice ignored the GP33 transgene expressed in hepatocytes. Ignorance of adoptively transferred TCR-tg cells in ALB1 mice was broken by infection with lymphocytic choriomeningitis virus, leading to induction of hepatitis in ALB1, but not in control, mice. Taken together, we have established a novel model of virus-induced CD8 T cell-mediated autoimmune hepatitis in mice and demonstrate that naive CD8 T cells may ignore Ags expressed in the liver.

Immunotherapy with dendritic cells and tumor major histocompatibility complex class I-derived peptides requires a high density of antigen on tumor cells

Immunization with dendritic cells and unfractionated MHC class I-binding peptides derived from autologous tumor cells has been shown to induce effective antitumor immunity. However, the importance of the relative abundance of tumor peptides on the surface of tumor cells is not known. We have addressed this question using peptides isolated from three tumor cell lines transfected with a minigene encoding amino acids 33-41 of the lymphocytic choriomeningitis virus glycoprotein (LCMV(33-41)). The three cell lines expressed different levels of MHC class I molecules and had different abilities to stimulate proliferation of LCMV(33-41)-specific T cells in vitro. We found that antitumor immune responses were best elicited by immunizing mice with dendritic cells and synthetic LCMV(33-41) peptide. Peptide preparations from a given tumor cell line conferred protection against challenge with the same tumor cell line. However, protective immunity to a different tumor could be induced only if the cell line used for peptide preparation presented a high relative proportion of LCMV(33-41) in association with MHC class I. Our results suggest that multiple peptide epitopes are required for the induction of an effective antitumor immune response using MHC class I-binding peptides from tumor cells. Also, the ability to induce an antitumor immune response appears to correlate with the proportion, rather than the absolute amount, of tumor-specific peptide in the mixture used for immunization.

CD8(+) T cells secreting type 2 lymphokines are defective in protection against viral infection

Effector T cells secreting type 1 and/or type 2 lymphokines (Tc1, Tc0, Tc2) were generated in vitro from CD8(+) T cells of mice with a transgenic TCR recognizing lymphocytic choriomeningitis virus (LCMV) glycoprotein to compare their effector function in vitro and in vivo. Tc1, Tc2, and Tc0 showed similar Fas- and perforin-mediated cytotoxicity in vitro. Upon adoptive transfer, Tc2 and Tc0 effectors were less efficient than Tc1 at controlling LCMV or recombinant vaccinia virus expressing the LCMV glycoprotein in vivo. Tc2 and Tc0 had decreased surface VLA-4 density and deficient activation-induced LFA-1/ICAM-1-dependent homotypic adhesion in vitro. Therefore, the reduced antiviral activity in vivo of Tc2 and Tc0 compared with Tc1 is not due to reduced cytotoxic activity or IFN-gamma secretion but may be explained by defective homing to the target organ due to decreased expression and/or lower activity of adhesion molecules.

Crucial role of TNF-alpha in CD8 T cell-mediated elimination of 3LL-A9 Lewis lung carcinoma cells in vivo

The role of perforin, IFN-gamma, and TNF-alpha in anti-tumor CD8 T cell immunity was examined in a new tumor model using a CD8 T cell epitope (GP33) derived from lymphocytic choriomeningitis virus as a tumor-associated Ag. In contrast with parental 3LL-A9 (A9) Lewis lung carcinoma cells that progressively grow in C57BL/6 mice, s.c. injection of GP33-transfected A9GP33 tumor cells induced a protective GP33-specific CD8 T cell response that led to complete tumor cell elimination. Tumor regression was dependent on perforin, IFN-gamma, or TNF-alpha, because A9GP33 tumors developed in mice deficient in one of these genes. A9GP33 tumors arising in perforin- and IFN-gamma-deficient mice represented GP33 Ag-loss variants, demonstrating that GP33-specific CD8 T cells from these mice were able to exert an Ag selection pressure. In contrast, tumor cells growing in TNF-alpha knock-out mice still expressed the tumor-associated GP33 peptide despite the presence of activated GP33-specific CD8 T cells. These findings provide evidence for a crucial role of TNF-alpha in A9 tumor cell elimination by CD8 T cells in vivo.

Quantitative Structure-Property Study on Pyrazines with Bell Pepper Flavor

A quantitative structure-property (QSPR) study on pyrazines with bell pepper aroma is performed by means of different statistical methods, which correlate appropriate molecular descriptors with the biological activity. The different methods lead to consistent results, indicating which of the molecular properties of the compounds under consideration are significant for bell pepper flavor. These results are compared with other models.

CpG-DNA activates in vivo T cell epitope presenting dendritic cells to trigger protective antiviral cytotoxic T cell responses

MHC class I-restricted T cell epitopes lack immunogenicity unless aided by IFA or CFA. In an attempt to circumvent the known inflammatory side effects of IFA and CFA, we analyzed the ability of immunostimulatory CpG-DNA to act as an adjuvant for MHC class I-restricted peptide epitopes. Using the immunodominant CD8 T cell epitopes, SIINFEKL from OVA or KAVYNFATM (gp33) from lymphocytic choriomeningitis virus glycoprotein, we observed that CpG-DNA conveyed immunogenicity to these epitopes leading to primary induction of peptide-specific CTL. Furthermore, vaccination with the lymphocytic choriomeningitis virus gp33 peptide triggered not only CTL but also protective antiviral defense. We also showed that MHC class I-restricted peptides are constitutively presented by immature dendritic cells (DC) within the draining lymph nodes but failed to induce CTL responses. The use of CpG-DNA as an adjuvant, however, initiated peptide presenting immature DC progression to professional licensed APC. Activated DC induced cytolytic CD8 T cells in wild-type mice and also mice deficient of Th cells or CD40 ligand. CpG-DNA thus incites CTL responses toward MHC class I-restricted T cell epitopes in a Th cell-independent manner. Overall, these results provide new insights into CpG-DNA-mediated adjuvanticity and may influence future vaccination strategies for infectious and perhaps tumor diseases.

Immune down-regulation and peripheral deletion of CD8 T cells does not require TNF receptor-ligand interactions nor CD95 (Fas, APO-1)

TNF receptor-ligand interactions and CD95 (Fas / APO-1) have been demonstrated to be involved in activation-induced death of mature T cells. Here, we examined the role of these molecules in the murine model of lymphocytic choriomeningitis virus (LCMV) infection using LCMV TCR transgenic (tg) mice lacking TNF, TNF receptor I (TNFR1), CD95 or both TNFR1 and CD95. This report demonstrates that neither TNF receptor-ligand interactions nor CD95 was required for down-regulation of LCMV-specific CD8 T cells following acute LCMV infection in vivo. Even LCMV-specific CD8 T cells lacking both TNFR1 and CD95 molecules declined after the acute phase of the infection with normal kinetics. Furthermore, peripheral deletion of LCMV-specific CD8 T cells induced by LCMV peptide injection or by adoptive transfer of tg spleen cells expressing the corresponding LCMV epitope was not impaired in mice lacking TNF, TNFR1 and / or CD95. Our data speak against an indispensable role of these molecules in antigen-induced apoptosis of CD8 T cells in vivo and suggest that T cell homeostasis after antigen challenge is controlled by additional mechanisms.

Distinct migration patterns of naive and effector CD8 T cells in the spleen: correlation with CCR7 receptor expression and chemokine reactivity

Changes in the migration pattern of lymphocytes represent a key event in the evolution of an immune response since they enable lymphocytes to gain access to infected tissues. We studied the location of virus-specific CD8 T cells in various splenic compartments in response to infection with lymphocytic choriomeningitis virus (LCMV), either in situ or by adoptive cell transfers using T cells from transgenic (tg) mice expressing an LCMV-specific TCR. Naive tg T cells were predominantly localized in the periarteriolar lymphoid sheath, where they proliferated extensively after virus infection. In contrast, in vivo activated effector T cells failed to enter white pulp areas and accumulated in the red pulp. The different homing patterns of naive and effector CD8 T cells in vivo correlated well with their CCR7 chemokine receptor expression and their reactivity to the secondary lymphoid tissue chemokine (SLC). Thus, down-regulation of CCR7 expression on CD8 effector T cells rendered them unre sponsive to SLC, which controls T cell homing into white pulp of spleen and lymph nodes. Exclusion of CD8 effector T cells from these sites may represent an important mechanism to protect professional antigen-presenting cells from cytotoxic T cell attack and thus to prevent a prematuredecline of the immune response.

T cell ignorance in mice to Borna disease virus can be overcome by peripheral expression of the viral nucleoprotein

Infection of neonates with Borna disease virus (BDV) induces severe meningoencephalitis and neurological disorder in wild-type but not in beta(2)-microglobulin-deficient mice of strain MRL (H-2(k)). Temporary in vivo depletion of CD8(+) T cells delayed BDV-induced disease for several weeks. Depletion of CD4(+) T cells had a similar beneficial effect, indicating that the BDV-induced neurological disorder in mice is a CD4(+) T cell-dependent immunopathological process that is mediated by CD8(+) T cells. Lymphocytes prepared from brains of diseased mice were mainly from the CD8(+) T cell subset. They showed up-regulation of activation markers and exerted strong MHC I-restricted cytotoxic activity against target cells expressing the BDV nucleoprotein p40. Infection of B10.BR (H-2(k)) or congenic C57BL/10 (H-2(b)) mice resulted in symptomless, lifelong persistence of BDV in the brain. Superinfection with a recombinant vaccinia virus expressing BDV p40 but not with other vaccinia viruses induced severe neurological disease and encephalitis in persistently infected B10.BR mice but not in persistently infected C57BL/10 mice, indicating that the disease-inducing T cell response is restricted to the nucleoprotein of BDV in H-2(k) mice. Our results demonstrate that the cellular arm of the immune system may ignore the presence of a replicating virus in the central nervous system until proper antigenic stimulation at a peripheral site triggers the antiviral response.

Identification of an alpha2,6-sialyltransferase induced early after lymphocyte activation

We have used mRNA differential display PCR to search for genes induced in activated T cells and we identified a gene encoding an alpha2,6-sialyltransferase (ST6GalNAc IV) that is rapidly induced in lymphocytes after antigen or mitogen stimulation. The 3.6 kb full-length cDNA clone (MK45) obtained contained a single open reading frame encoding a 302 amino acid protein and a 2.5 kb 3' untranslated region. MK45 expression in in vivo-activated CD8 T cells reached the highest level 4 h after antigen triggering and then declined rapidly to nearly base levels within 45 h. Northern blot analysis further revealed that MK45 expression was also induced in LPS-activated B cells and antigen-triggered CD4 T cells in vitro. MK45 expression was low or undetectable in most other mouse tissues examined, when compared to activated lymphocytes. Importantly, the mRNA expression level of other sialyltransferases remained largely unchanged during the early stage of lymphocyte activation. Finally, increased ecto-sialyltransferase activity and an altered sialylation pattern were demonstrated on the cell surface of early activated CD8 T cells. Our report identifies a candidate sialyltransferase gene that is involved in the early alteration of the sialylation pattern of cell surface molecules in activated lymphocytes.

A novel approach to visualize polyclonal virus-specific CD8 T cells in vivo

Recent technical breakthroughs in generating soluble MHC class I-peptide tetramers now allow the direct visualization of virus-specific CD8 T cells after infection in vivo. However, this technique requires the knowledge of the immunodominant viral epitopes recognized by T cells. Here, we describe an alternative approach to visualize polyclonal virus-specific CD8 T cells in vivo using a simple adoptive transfer system. In our approach, C57BL/6 (Thy1.2) mice were infected with lymphocytic choriomeningitis virus, vesicular stomatitis virus, or vaccinia virus to induce virus-specific memory T cells. Tracer T cells (2 x 106) from these virus-immune mice were adoptively transferred into nonirradiated (C57BL/6 x B6.PL-Thy-1a)F1 mice. After infection of the F1-recipient mice with the appropriate virus, the transferred cells expanded vigorously, and on day 8 postinfection 60-80% of total CD8 T cells were of donor T cell origin. Under the same conditions memory CD4 T cells gave rise to at least 10 times less cell numbers than memory CD8 T cells. The transfer system described here not only allows to visualize effector and memory CD8 T cells in vivo but also to isolate them for further in vitro characterization without knowing the epitopes recognized by these Ag-specific CD8 T cells.

Intrathymic deletion of MHC class I-restricted cytotoxic T cell precursors by constitutive cross-presentation of exogenous antigen

Cross-priming of cytotoxic T lymphocytes by professional antigen-presenting cells (APC) is a potential hazard to self tolerance because it exposes naive T cells to tissue-specific self antigens in the context of co-stimulatory signals. Here we show that cross-presentation of exogenous material occurs constitutively within the thymus. Although efficient cross-presentation is a property of relatively few APC it results in thymocyte deletion both in vitro and in vivo, suggesting that intrathymic cross-presentation can operate as an effective component of tolerance to circulating self antigens. The capacity of minor cell populations to mediate thymocyte deletion but not positive selection reflects an underlying difference in the biology of these two processes.

Molecular cloning and functional expression of two members of mouse NeuAcalpha2,3Galbeta1,3GalNAc GalNAcalpha2,6-sialyltransferase family, ST6GalNAc III and IV

Two cDNA clones encoding NeuAcalpha2,3Galbeta1,3GalNAc GalNAcalpha2, 6-sialyltransferase have been isolated from mouse brain cDNA libraries. One of the cDNA clones is a homologue of previously reported rat ST6GalNAc III according to the amino acid sequence identity (94.4%) and the substrate specificity of the expressed recombinant enzyme, while the other cDNA clone includes an open reading frame coding for 302 amino acids. The deduced amino acid sequence is not identical to those of other cloned mouse sialyltransferases, although it shows the highest sequence similarity with mouse ST6GalNAc III (43.0%). The expressed soluble recombinant enzyme exhibited activity toward NeuAcalpha2, 3Galbeta1, 3GalNAc, fetuin, and GM1b, while no significant activity was detected toward Galbeta1,3GalNAc or asialofetuin, or the other glycoprotein substrates tested. The sialidase sensitivity of the 14C-sialylated residue of fetuin, which was sialylated by this enzyme with CMP-[14C]NeuAc, was the same as that of ST6GalNAc III. These results indicate that the expressed enzyme is a new type of GalNAcalpha2,6-sialyltransferase, which requires sialic acid residues linked to Galbeta1,3GalNAc residues for its activity; therefore, we designated it mouse ST6GalNAc IV. Although the substrate specificity of this enzyme is similar to that of ST6GalNAc III, ST6GalNAc IV prefers O-glycans to glycolipids. Glycolipids, however, are better substrates for ST6GalNAc III.

Qualitative and quantitative requirements for CD4+ T cell-mediated antiviral protection

CD4+ Th cells deliver the cognate and cytokine signals that promote the production of protective virus-neutralizing IgG by specific B cells and are also able to mediate direct antiviral effector functions. To quantitatively and qualitatively analyze the antiviral functions of CD4+ Th cells, we generated transgenic mice (tg7) expressing an MHC class II (I-Ab)-restricted TCR specific for a peptide derived from the glycoprotein (G) of vesicular stomatitis virus (VSV). The elevated precursor frequency of naive VSV-specific Th cells in tg7 mice led to a markedly accelerated and enhanced class switching to virus-neutralizing IgG after immunization with inactivated VSV. Furthermore, in contrast to nontransgenic controls, tg7 mice rapidly cleared a recombinant vaccinia virus expressing the VSV-G (Vacc-IND-G) from peripheral organs. By adoptive transfer of naive tg7 CD4+ T cells into T cell-deficient recipients, we found that 105 transferred CD4+ T cells were sufficient to induce isotype switching after challenge with a suboptimal dose of inactivated VSV. In contrast, naive transgenic CD4+ T cells were unable to adoptively confer protection against peripheral infection with Vacc-IND-G. However, tg7 CD4+ T cells that had been primed in vitro with VSV-G peptide were able to adoptively transfer protection against Vacc-IND-G. These results demonstrate that the antiviral properties of CD4+ T cells are governed by the differentiation status of the CD4+ T cell and by the type of effector response required for virus elimination.

Protection against lymphocytic choriomeningitis virus infection induced by a reduced peptide bond analogue of the H-2Db-restricted CD8(+) T cell epitope GP33

Recent investigations have suggested that pseudopeptides containing modified peptide bonds might advantageously replace natural peptides in therapeutic strategies. We have generated eight reduced peptide bond Psi(CH2-NH) analogues corresponding to the H-2Db-restricted CD8(+) T cell epitope (called GP33) of the glycoprotein of the lymphocytic choriomeningitis virus. One of these pseudopeptides, containing a reduced peptide bond between residues 6 and 7 (Psi(6-7)), displayed very similar properties of binding to major histocompatibility complex (MHC) and recognition by T cell receptor transgenic T cells specific for GP33 when compared with the parent peptide. We assessed in vitro and in vivo the proteolytic resistance of GP33 and Psi(6-7) and analyzed its contribution to the priming properties of these peptides. The Psi(6-7) analogue exhibited a dramatically increased proteolytic resistance when compared with GP33, and we show for the first time that MHC-peptide complexes formed in vivo with a pseudopeptide display a sustained half-life compared with the complexes formed with the natural peptide. Furthermore, in contrast to immunizations with GP33, three injections of Psi(6-7) in saline induced significant antiviral protection in mice. The enhanced ability of Psi(6-7) to induce antiviral protection may result from the higher stability of the analogue and/or of the MHC-analogue complexes.

Kinetics of the response of naive and memory CD8 T cells to antigen: similarities and differences

We have studied the kinetics of the antigen induced response of naive and memory CD8 T cells expressing a transgenic T cell receptor (TCR) specific for the glycoprotein peptide amino acid 33-41 (GP33) of the lymphocytic choriomeningitis virus (LCMV). Memory T cells were generated in vivo by adoptive transfer of LCMV TCR transgenic T cells into normal recipient mice, followed by LCMV infection. The results demonstrated that the cell cycle progression and kinetics of TCR down-modulation, CD25 and CD69 up-regulation were identical in naive and memory T cells after antigen recognition. Moreover, the two T cell populations did not differ in respect of activation thresholds and in their proliferative capacities neither in vitro nor in vivo. However, memory CD8 T cells could be more rapidly induced to become cytolytic and to secrete high levels of interleukin-2 and interferon-gamma than naive T cells. LCMV GP33-specific CD8 memory T cells were only slightly more efficient in reducing LCMV titers in the spleen but were far more effective than naive LCMV GP33-specific T cells in controlling subcutaneous tumor growth of B16.F10 melanoma cells which expressed the LCMV GP33 epitope as tumor-associated antigen. Thus, in our experiments the main difference between CD8 memory T cells and naive cells is the ability of the former to rapidly acquire effector cell functions.

Virus-activated CD8 T cells and lymphokine-activated NK cells express the mast cell function-associated antigen, an inhibitory C-type lectin

The mast cell function-associated Ag (MAFA) is an inhibitory C-type lectin that was originally identified on the cell surface of a rat mucosal mast cell line, RBL-2H3. We have cloned the mouse homologue of the rat MAFA gene, and Northern blot analysis revealed that mouse MAFA (mMAFA) gene expression was strongly induced in effector CD8 T cells and lymphokine-activated NK cells but not in effector CD4 T cells and in mouse mast cells. Moreover, mMAFA gene expression was only found in effector CD8 T cells that had been primed in vivo with live virus because in vitro activated CD8 T cells did not express mMAFA. Primary sequence comparison revealed a high degree of conservation (89% similarity) between rat MAFA and mMAFA. Thus, the MAFA molecule in the mouse is a putative inhibitory receptor on anti-viral CD8 T cells induced in vivo and on NK cells.

Antigen persistence and time of T-cell tolerization determine the efficacy of tolerization protocols for prevention of skin graft rejection

We studied antigen-specific T-cell tolerization therapy using skin transplantation across a defined minor histocompatibility antigen difference. Specific tolerization protocols using short-lived peptide or long-lived spleen cells presenting the peptide as antigen prevented graft rejection without immunosuppression when started before or as long as 10 days after transplantation. Peptide-induced T-cell tolerance was transient, and antigen presentation by the graft was not sufficient to maintain tolerance. In contrast, transfer of antigen-expressing lymphoid cells induced long-lasting tolerance correlating with donor cell chimerism. These findings show that antigen-specific tolerization can induce graft acceptance even when begun after transplantation and that long-term graft survival depends on persistence of the tolerizing antigen.

Tumor-infiltrating lymphocytes exhibiting high ex vivo cytolytic activity fail to prevent murine melanoma tumor growth in vivo

The identification of tumor-associated Ags recognized by CD8+ CTL and prevention of tumor outgrowth by adoptive transfer of these CTL demonstrates that CD8+ T cells play a major role in antitumor immunity. We have generated B16.F10 melanoma cells that express the glycoprotein epitope amino acid 33-41 (GP33) of the lymphocytic choriomeningitis virus (LCMV) to examine antitumor CD8+ T cell response in C57BL/6 mice immune to LCMV and in mice transgenic for the LCMV GP33-specific P14 TCR (P14 TCR mice). We find that B16.F10GP33 tumor cells grew in syngeneic C57BL/6 mice without inducing T cell tolerance. LCMV infection or adoptive transfer of LCMV-specific effector T cells delayed but did not prevent growth of preestablished tumors in these mice. However, B16.F10GP33 tumor cells were rejected in mice immune to LCMV and in mice treated with LCMV-specific effector T cells on the same day as the tumor. Surprisingly, B16.F10GP33 tumor cells grew in P14 TCR transgenic mice despite an abundance of tumor-associated Ag-specific CD8+ T cells. In these mice, freshly isolated tumor-infiltrating lymphocytes exhibited an activated phenotype and displayed high GP33-specific cytolytic activity when assessed ex vivo. Thus, B16.F10GP33 melanoma cells are able to initiate, but not to sustain, a GP33-specific CTL response sufficient to clear the tumor enduringly.

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

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

Viral and bacterial infections interfere with peripheral tolerance induction and activate CD8+ T cells to cause immunopathology

We studied the impact of various infectious and proinflammatory agents on the induction of peripheral T cell tolerance. Adoptive transfer of CD8+ T cells from lymphocytic choriomeningitis virus (LCMV) T cell receptor transgenic mice into LCMV antigen transgenic mice expressing the LCMV glycoprotein epitope (gp) 33-41 under control of a major histocompatibility complex class I promoter led to efficient induction of peripheral tolerance after a period of transient activation. If, however, the recipient mice were challenged with viral or bacterial infections or proinflammatory agents (lipopolysaccharide or Poly:IC) early after cell transfer, tolerance induction was prevented and instead, CD8+ T cell activation leading to vigorous expansion and generation of cytolytic activity ensued. This became manifest in significant immunopathology mainly involving destruction of the splenic architecture and lysis of antigen-expressing lymphocyte and macrophage populations. Important parameters involved in the activation of host-reactive T cells by nonspecific infectious agents included the presence, localization, and quantity of the specific transgene-encoded self-antigen; in contrast, CD4+ T cells were not required. In mice surviving the acute phase, the transferred CD8+ T cells persisted at high levels in an anergic state; they were unable to generate cytolytic activity in vitro or to control LCMV infection in vivo. These results impinge on our understanding of the role of infectious agents in graft verus host reactions towards minor histocompatibility antigens.

Constitutive expression of Bcl-xL or Bcl-2 prevents peptide antigen-induced T cell deletion but does not influence T cell homeostasis after a viral infection

We examined the CD8+ T cell response to lymphocytic choriomeningitis virus (LCMV) in mice doubly transgenic for an LCMV-specific TCR and for either bcl-xL or bcl-2. Clonal down-sizing of the anti-viral CD8+ T cell response and the generation of T cell memory was not influenced by constitutive expression of these anti-apoptotic proteins in T cells. Expression of Bcl-xL or Bcl-2 did, however, prevent LCMV peptide-induced peripheral deletion of mature CD8+ T cells in vivo and apoptosis of activated LCMV-specific effector T cells in vitro. The CD8+ T cells "rescued" by Bcl-xL or Bcl-2 from peptide antigen-induced cell death were anergic and this could not be reversed by addition of IL-2 in vitro or by adoptive transfer into antigen-free recipient mice followed by LCMV infection in vivo. Taken together, we show here that 1) Bcl-xL or Bcl-2 are functionally equivalent in their ability to modulate CD8+ T cell survival in vivo, 2) distinct apoptosis signaling pathways exist in CD8+ T cells, one that can be inhibited by Bcl-2 or Bcl-xL and one that cannot be blocked, and 3) apoptosis of CD8+ effector T cells during the declining phase of an immune response is not prevented by constitutive expression of the anti-apoptotic proteins Bcl-xL and Bcl-2.

An adult thymic stromal-cell suspension model for in vitro positive selection

Presented here is a cell-suspension model for positive selection using thymocytes from alphabeta-TCR (H-2Db-restricted) transgenic mice specific to the lymphocytic choriomeningitis virus (LCMV) on a nonselecting MHC background (H-2d or TAP-1 -/-), cocultured with freshly isolated adult thymus stromal cells of the selecting MHC type. The thymic stromal cells alone induced positive selection of functional CD4- CD8+ cells whose kinetics and efficiency were enhanced by nominal peptide. Fibroblasts expressing the selecting MHC alone did not induce positive selection; however, together with nonselecting stroma and nominal peptide, there was inefficient positive. These results suggest multiple signaling in positive selection with selection events able to occur on multiple-cell types. The ease with which this model can be manipulated should greatly facilitate the resolution of the mechanisms of positive selection in normal and pathological states.

Differentiation of CD4(high)CD8(low) coreceptor-skewed thymocytes into mature CD8 single-positive cells independent of MHC class I recognition

Thymocytes with a CD4(hi)CD8(lo) coreceptor-skewed (CRS) phenotype have been shown to contain precursors for CD8 single-positive (SP) thymocytes, in addition to precursors for CD4 SP cells. The selection mechanisms that stimulate CD4(hi)CD8(lo) cells to revert to the CD8 lineage are not known. Mice transgenic (tg) for the major histocompatibility complex (MHC) class I-restricted P14 T cell receptor (TCR), on the H-2bm13 background, generate a large number of CD4(hi)CD8(lo) CRS thymocytes. We analyzed the developmental potential and the differentiation requirements of the CD4(hi)CD8(lo) population of these mice. Using reaggregate thymic organ cultures (RTOC), we observed that these cells efficiently and almost exclusively differentiate into CD8 SP cells. Differentiation occurred independent of whether or not the MHC haplotype of the thymic stroma corresponds to the MHC restriction of the tg TCR. Loss of CD4 was independent of thymic stroma, up-regulation of CD8 to full levels was dependent on thymic stroma but independent of MHC haplotype. After trypsin treatment and overnight incubation, these CRS cells re-expressed CD8 but failed to re-express CD4, indicating that they are in the process of terminating CD4 synthesis. CD8 SP cells derived from the CRS cells proliferate in response to peptide-pulsed antigen-presenting cells. Our data suggest that CD4(hi)CD8(lo) CRS thymocytes bearing the P14 tg TCR have completed positive selection and differentiate autonomously into functionally competent CD8 SP cells.

Peptide antigen treatment of naive and virus-immune mice: antigen-specific tolerance versus immunopathology

Peptide-specific down-regulation of T cell responses may represent a powerful tool to intervene in autoimmune diseases or graft rejections. It is therefore important to know whether peptide treatment tolerizes both naive and antigen-experienced memory T lymphocytes. Here we show that a major histocompatibility complex class I binding peptide, derived from the glycoprotein (GP33 peptide) of lymphocytic choriomeningitis virus (LCMV), specifically tolerized naive cytotoxic T lymphocytes (CTL) when administered three times intraperitoneally in incomplete Freund's adjuvants. However, in the presence of GP33-specific memory CTL in LCMV-primed mice, the same treatment had a general immunosuppressive effect on unrelated third-party antigen-specific T cell responses and caused severe immunopathological damage to the spleen.

Alterations in the level of CD45 surface expression affect the outcome of thymic selection

CD45 is a receptor protein tyrosine phosphatase whose activity is required for thymocyte development and TCR-mediated signal transduction. Here we show that positive selection of TCR-alphabeta transgenic thymocytes is completely blocked in CD45 exon 6 -/- gene-deficient (CD45 -/-) mice that express the P14 TCR specific for the lymphocytic choriomeningitis virus. Thymocytes from mice heterozygous for the targeted disruption of the CD45 gene (CD45 +/-) displayed a reduction in both CD45 surface intensity and enzymatic CD45 protein tyrosine phosphatase activity. Surprisingly, positive thymocyte selection was enhanced in CD45 +/- mice as characterized by an up-regulation of the P14 TCR on thymocytes and increased numbers of transgenic T cells. Using a variant of lymphocytic choriomeningitis virus that is impaired in the induction of negative selection of P14 thymocytes, we also show that the reduction of CD45 surface expression in CD45 +/- mice rendered P14 transgene thymocytes susceptible to negative selection. These data demonstrate that changes in the expression level of the receptor protein tyrosine phosphatase CD45 can alter thymic selection.

Alterations in the level of CD45 surface expression affect the outcome of thymic selection

CD45 is a receptor protein tyrosine phosphatase whose activity is required for thymocyte development and TCR-mediated signal transduction. Here we show that positive selection of TCR-alphabeta transgenic thymocytes is completely blocked in CD45 exon 6 -/- gene-deficient (CD45 -/-) mice that express the P14 TCR specific for the lymphocytic choriomeningitis virus. Thymocytes from mice heterozygous for the targeted disruption of the CD45 gene (CD45 +/-) displayed a reduction in both CD45 surface intensity and enzymatic CD45 protein tyrosine phosphatase activity. Surprisingly, positive thymocyte selection was enhanced in CD45 +/- mice as characterized by an up-regulation of the P14 TCR on thymocytes and increased numbers of transgenic T cells. Using a variant of lymphocytic choriomeningitis virus that is impaired in the induction of negative selection of P14 thymocytes, we also show that the reduction of CD45 surface expression in CD45 +/- mice rendered P14 transgene thymocytes susceptible to negative selection. These data demonstrate that changes in the expression level of the receptor protein tyrosine phosphatase CD45 can alter thymic selection.