A mouse aminopeptidase N is a marker for antigen-presenting cells and appears to be co-expressed with major histocompatibility complex class II molecules

Molecular characterization of methionine aminopeptidase1 from Eimeria tenella

Coccidiosis, a serious intestinal parasitic disease caused by Eimeria spp., can result in huge annual economic losses to the poultry industry worldwide. At present, coccidiosis is mainly controlled by anticoccidial drugs. However, drug resistance has developed in Eimeria because of the long-term and unreasonable use of the drugs currently available. In our previous study, RNA-seq showed that the expression of methionine aminopeptidase1 (EtMetAP1) was up-regulated in diclazuril-resistant (DZR) and maduramicin-resistant (MRR) strains compared to drug-sensitive (DS) strain of Eimeria tenella. In this study, EtMetAP1 was cloned and expressed, and the function and characteristics of the EtMetAP1 protein were analyzed. The transcription and translation levels of EtMetAP1 in DS strain of E. tenella at different developmental stages were analyzed by qPCR and western blotting. We found that the transcription and translation levels of EtMetAP1 in second-generation merozoites (SM) were higher than those of the other three stages (unsporulated oocyst, sporulated oocyst, and sporozoites). Simultaneously, qPCR was used to analyze the mRNA transcription levels of EtMetAP1 in DS, DZR, MRR, and salinomycin-resistant (SMR) strain. The results showed that compared to the sensitive strain, the transcription levels of EtMetAP1 in DZR and MRR were up-regulated. There was no significant difference in transcription level in SMR. Indirect immunofluorescence localization showed that the protein was mainly localised in the cell membrane and cytoplasm of sporozoites and SM. An invasion inhibition test showed that anti-rEtMetAP1 polyclonal antibody could effectively inhibit the sporozoite invasion of host cells. These results suggest that the protein may be involved in the growth and development of parasites in host cells, the generation of drug resistance, and host cell invasion.

Epigallocatechin Gallate (EGCG) Promotes the Immune Function of Ileum in High Fat Diet Fed Mice by Regulating Gut Microbiome Profiling and Immunoglobulin Production

This study aimed to investigate the regulatory effect of epigallocatechin gallate (EGCG) on the composition of the gut microbiome, the transcriptomic profiling of ileum, and their interplay in high fat diet (HFD) induced obese mice. Intragastric administration of EGCG to C57BL/6J mice for 14 consecutive weeks remarkably decreased HFD induced excessive fat deposition (p < 0.001), and the increment of serum TG, TC, HDL-C (p < 0.05), as well as improved glucose tolerance (p < 0.001). EGCG shifted the gut microbiota mainly by elevating the relative abundance of Parasutterrlla, Bacteroides, and Akkermansia (p < 0.01), decreasing that of norank_f_Erysipelotrichaceae, unclassified_f_Ruminococcaceae, Anaerotruncus, Roseburia, norank_Lachnospiraceae, and Lachnospiraceae_UCG_006 (p < 0.01) at the genus level. In addition, EGCG affected the transcriptomic profiling of ileum, and the differentially expressed (DE) genes after HFD or/and EGCG treatment were mostly enriched in the immune reaction of ileum, such as the GO term of “immune effector process” and “phagocytosis, recognition.” Furthermore, the KEGG category of “immune diseases,” “immune system,” and “infection diseases: bacterial” were commonly enriched by the DE genes of the two treatments. Among those DE genes, 16 immunoglobulins heavy chain variable region encoded genes (Ighvs) and other immunity-related genes, such as complement component 2 (C2), interferon-induced transmembrane protein 1 (Iftm1), polymeric immunoglobulin receptor (pigR), and alanyl aminopeptidase (Anpep), were highly correlated with the shifted microbes in the gut (p < 0.05, absolute r > 0.5). Overall, the results suggested that EGCG ameliorated the HFD induced metabolic disorder mainly by regulating gut microbiome profiling and the immunoglobulin production of ileum, while the genes expressed in the ileum, especially Ighvs, C2, Iftm1, pigR, and Anpep, might play important roles in coordinating the immunity of mice regarding the gut microbes and the host interactions.

CD13/Aminopeptidase N Is a Potential Therapeutic Target for Inflammatory Disorders

CD13/aminopeptidase N is a widely expressed ectoenzyme with multiple functions. As an enzyme, CD13 regulates activities of numerous cytokines by cleaving their N-terminals and is involved in Ag processing by trimming the peptides bound to MHC class II. Independent of its enzymatic activity, cell membrane CD13 functions by cross-linking-induced signal transduction, regulation of receptor recycling, enhancement of FcγR-mediated phagocytosis, and acting as a receptor for cytokines. Moreover, soluble CD13 has multiple proinflammatory roles mediated by binding to G-protein-coupled receptors. CD13 not only modulates development and activities of immune-related cells, but also regulates functions of inflammatory mediators. Therefore, CD13 is important in the pathogenesis of various inflammatory disorders. Inhibitors of CD13 have shown impressive anti-inflammatory effects, but none of them has yet been used for clinical therapy of human inflammatory diseases. We reevaluate CD13's regulatory role in inflammation and suggest that CD13 could be a potential therapeutic target for inflammatory disorders.

Reduced DEAF1 function during type 1 diabetes inhibits translation in lymph node stromal cells by suppressing Eif4g3

The transcriptional regulator deformed epidermal autoregulatory factor 1 (DEAF1) has been suggested to play a role in maintaining peripheral tolerance by controlling the transcription of peripheral tissue antigen genes in lymph node stromal cells (LNSCs). Here, we demonstrate that DEAF1 also regulates the translation of genes in LNSCs by controlling the transcription of the poorly characterized eukaryotic translation initiation factor 4 gamma 3 (Eif4g3) that encodes eIF4GII. Eif4g3 gene expression was reduced in the pancreatic lymph nodes of Deaf1-KO mice, non-obese diabetic mice, and type 1 diabetes patients, where functional Deaf1 is absent or diminished. Silencing of Deaf1 reduced Eif4g3 expression, but increased the expression of Caspase 3, a serine protease that degrades eIF4GII. Polysome profiling showed that reduced Eif4g3 expression in LNSCs resulted in the diminished translation of various genes, including Anpep, the gene for aminopeptidase N, an enzyme involved in fine-tuning antigen presentation on major histocompatibility complex (MHC) class II. Together these findings suggest that reduced DEAF1 function, and subsequent loss of Eif4g3 transcription may affect peripheral tissue antigen (PTA) expression in LNSCs and contribute to the pathology of T1D.

Perinatal undernutrition alters intestinal alkaline phosphatase and its main transcription factors KLF4 and Cdx1 in adult offspring fed a high-fat diet

Nutrient restriction during gestation and/or suckling is associated with an increased risk of developing inflammation, obesity and metabolic diseases in adulthood. However, the underlying mechanisms, including the role of the small intestine, are unclear. We hypothesized that intestinal adaptation to the diet in adulthood is modulated by perinatal nutrition. This hypothesis was tested using a split-plot design experiment with 20 controls and 20 intrauterine growth-retarded (IUGR) rats aged 240 days and randomly assigned to be fed a standard chow or a high-fat (HF) diet for 10 days. Jejunal tissue was collected at necropsy and analyzed for anatomy, digestive enzymes, goblet cells and mRNA levels. Cecal contents and blood serum were analyzed for alkaline phosphatase (AP). IUGR rats failed to adapt to HF by increasing AP activity in jejunal tissue and cecal content as observed in controls. mRNA levels of transcription factors KLF4 and Cdx1 were blunted in jejunal epithelial cell of IUGR rats fed HF. mRNA levels of TNF-α were lower in IUGR rats. They also displayed exacerbated aminopeptidase N response and reduced jejunal goblet cell density. Villus and crypt architecture and epithelial cell proliferation increased with HF in both control and IUGR rats. Serum AP tended to be lower, and serum levamisole inhibition-resistant AP fraction was lower, in IUGR than controls with HF. Serum fatty acids and triglycerides were higher in IUGR rats and higher with HF. In conclusion, the adult intestine adapts to an HF diet differentially depending on early nutrition, jejunal AP and transcription factors being blunted in IUGR individuals fed HF.

Anti-CD13 Abs in children with extensive chronic GVHD and their relation to soluble CD13 after allogeneic blood and marrow transplantation from a Children's Oncology Groups Study, ASCT0031

Our group previous demonstrated a strong association between elevated plasma soluble CD13 enzyme activity and newly diagnosed extensive chronic graft-versus-host disease (cGVHD) in children. Since cytotoxic anti-CD13 antibodies have been documented after blood and marrow transplant in association with cytomegalovirus infection and cGVHD, we hypothesized soluble CD13 contributes to cGVHD pathogenesis by induction of CD13 reactive antibodies and that anti-CD13 antibodies could be additional biomarkers for newly diagnosed pediatric extensive cGVHD. Using prospectively collected plasma samples from pediatric allogeneic blood and marrow transplant subjects with cGVHD and controls without cGVHD enrolled in a large multi-institution Children's Oncology Group cGVHD therapeutic trial we evaluated whether soluble CD13 correlates with induction of anti-CD13 antibodies. We found that CD13 reactive antibodies are present in a proportion of patients after allogeneic BMT, but did not appear to correlate with the presence of soluble CD13. Anti-CD13 antibodies also did not meet our criteria as a diagnostic biomarker for cGVHD. These data are not able to confirm that induction of CD13 reactive antibodies is a mechanism for cGVHD in children nor are part of the pathogenesis of cGVHD associated with elevated soluble CD13. The exact role of CD13 in cGVHD remains to be determined.

Distribution of dipeptidyl peptidase IV in patients with chronic tonsillitis

In the pathogeneses of recurrent tonsillitis (RT) and tonsillar hypertrophy (TH), different immunological mechanisms are involved. Dipeptidyl peptidase IV (DPP IV) and aminopeptidase N (APN) participate in the regulation of the immune response during inflammation. In this study, the localization of DPP IV and the enzymatic activities of DPP IV and APN in 32 patients, 13 with RT and 19 with TH, who underwent tonsillectomy were investigated. The localization of DPP IV in tonsils was studied using histochemical and immunohistochemical methods. The enzymatic activities of DPP IV and APN in tonsillar lymphocytes and the patients' sera were determined kinetically at 37 degrees C using Gly-Pro-p-nitroanilide (for DPP IV) and Ala-p-nitroanilide (for APN) as chromogenic substrates. In samples from both RT and TH patients, DPP IV was found to localize mainly in extrafollicular areas of tonsillar tissue in a pattern corresponding to the T-cell distribution. Significantly higher (P < 0.001) levels of DPP IV and APN activities in sera from patients with TH than in sera from patients with RT were found. A correlation of DPP IV activities in sera and tonsillar lymphocytes from patients with TH was also found (r = 0.518; P < 0.05). Moreover, the results show that DPP IV and APN activities in sera decreased significantly with age. Tonsillar lymphocytes demonstrated a wide range of DPP IV and APN activities, without significant differences between the investigated groups. The results of this study show that the localization of DPP IV does not depend on the type of tonsillitis, whereas the variety in levels of DPP IV and APN activities in sera of patients with TH and RT suggests different patterns of participation of antigen-stimulated tonsils in the immune system.

Specific and redundant roles for NFAT transcription factors in the expression of mast cell-derived cytokines

By virtue of their ability to express a plethora of biologically highly active mediators, mast cells (MC) are involved in both adaptive and innate immune responses. MC-derived Th2-type cytokines are thought to act as local amplifiers of Th2 reactions, including chronic inflammatory disorders such as allergic asthma, whereas MC-derived TNF-alpha is a critical initiator of antimicrobial defense. In this study, we demonstrate that the transcription factors NFATc1 and NFATc2 are part of a MC-specific signaling network that regulates the expression of TNF-alpha and IL-13, whereas NFATc3 is dispensable. Primary murine bone marrow-derived MC from NFATc2(-/-) mice, activated by either ionomycin or IgE/Ag cross-link, display a strong reduction in the production of these cytokines, compared with bone marrow-derived MC from wild-type mice. Detailed analyses of TNF-alpha and IL-13 expression using small interfering RNA-mediated knockdown reveals that both NFATc2 and NFATc1 are able to drive the expression of these cytokines, whereas neither degranulation nor the expression of IL-6 depends on NFAT activity. These results support the view that high NFAT activity is necessary for TNF-alpha and IL-13 promoter induction in MC, irrespective of whether NFATc2 or NFATc1 or a combination of both is present.

CD13/Aminopeptidase N overexpression by basic fibroblast growth factor mediates enhanced invasiveness of 1F6 human melanoma cells

CD13/Aminopeptidase N (CD13) is known to play an important role in tumour cell invasion. We examined whether basic fibroblast growth factor (bFGF) is involved in the regulation of CD13 expression in human melanoma cells. 1F6 human melanoma cells were stably transfected with constructs encoding either the 18 kDa (18kD) or all (ALL) bFGF isoform proteins. We observed highly increased CD13 mRNA and protein expression in the 1F6 clones regardless of the overexpression of either the 18kD or all isoform proteins. Neutral aminopeptidase activity was increased five-fold and could be inhibited by bestatin and the CD13-neutralising antibody WM15. The enhanced invasion through Matrigel, but not migration in a wound assay, was efficiently abrogated by both bestatin and WM15. Upregulation of CD13 expression was the result of increased epithelial and myeloid promoter activity up to 4.5-fold in 1F6-18kD and 1F6-ALL clones. Interestingly, in a panel of human melanoma cell lines, a significant correlation (r²=0.883, P<0.05) between bFGF and CD13 mRNA and protein expression was detected. High bFGF and CD13 expression were clearly related with an aggressive phenotype. Taken together, our data indicate that high bFGF expression upregulates CD13 expression in human melanoma cells by activating both the myeloid and the epithelial CD13 promoter. In addition, we show that high bFGF and CD13 expression results in enhanced invasive capacity and metastatic behaviour of human melanoma cells.

Glioma virotherapy: effects of innate immune suppression and increased viral replication capacity

Oncolytic viruses are genetically altered replication-competent viruses that infect, and reproduce in, cancer cells but do not harm normal cells. On lysis of the infected cells, the newly formed viruses burst out and infect other tumor cells. Experiments with injecting mutant herpes simplex virus 1 (hrR3) into glioma implanted in brains of rats show lack of efficacy in eradicating the cancer. This failure is attributed to interference by the immune system. Initial pretreatment with immunosuppressive agent cyclophosphamide reduces the percentage of immune cells. We introduce a mathematical model and use it to determine how different protocols of cyclophosphamide treatment and how increased burst size of the mutated virus will affect the growth of the cancer. One of our conclusions is that the diameter of the cancer will decrease from 4 mm to eventually 1 mm if the burst size of the virus is triple that which is currently available. The effect of repeated cyclophosphamide treatment is to maintain a low density of uninfected cells in the tumor, thus reducing the probability of migration of tumor cells to other locations in the brain.

Identification of genes modulated in rheumatoid arthritis using complementary DNA microarray analysis of lymphoblastoid B cell lines from disease-discordant monozygotic twins

OBJECTIVE

To identify disease-specific gene expression profiles in patients with rheumatoid arthritis (RA), using complementary DNA (cDNA) microarray analyses on lymphoblastoid B cell lines (LCLs) derived from RA-discordant monozygotic (MZ) twins.

METHODS

The cDNA was prepared from LCLs derived from the peripheral blood of 11 pairs of RA-discordant MZ twins. The RA twin cDNA was labeled with cy5 fluorescent dye, and the cDNA of the healthy co-twin was labeled with cy3. To determine relative expression profiles, cDNA from each twin pair was combined and hybridized on 20,000-element microarray chips. Immunohistochemistry and real-time polymerase chain reaction were used to detect the expression of selected gene products in synovial tissue from patients with RA compared with patients with osteoarthritis and normal healthy controls.

RESULTS

In RA twin LCLs compared with healthy co-twin LCLs, 1,163 transcripts were significantly differentially expressed. Of these, 747 were overexpressed and 416 were underexpressed. Gene ontology analysis revealed many genes known to play a role in apoptosis, angiogenesis, proteolysis, and signaling. The 3 most significantly overexpressed genes were laeverin (a novel enzyme with sequence homology to CD13), 11beta-hydroxysteroid dehydrogenase type 2 (a steroid pathway enzyme), and cysteine-rich, angiogenic inducer 61 (a known angiogenic factor). The products of these genes, heretofore uncharacterized in RA, were all abundantly expressed in RA synovial tissues.

CONCLUSION

Microarray cDNA analysis of peripheral blood-derived LCLs from well-controlled patient populations is a useful tool to detect RA-relevant genes and could help in identifying novel therapeutic targets.

Targeted delivery of IFNgamma to tumor vessels uncouples antitumor from counterregulatory mechanisms

Because of its immunomodulatory and anticancer activities, IFNgamma has been used as an anticancer drug in several clinical studies, unfortunately with modest results. Attempts to increase the response by increasing the dose or by repeated continuous injection often resulted in lower efficacy, likely due to counterregulatory effects. We show here that targeted delivery of low doses of IFNgamma to CD13, a marker of angiogenic vessels, can overcome major counterregulatory mechanisms and delay tumor growth in two murine models that respond poorly to IFNgamma. Tumor vascular targeting was achieved by coupling IFNgamma to GCNGRC, a CD13 ligand, by genetic engineering technology. The dose-response curve was bell-shaped. Maximal effects were induced with a dose of 0.005 microg/kg, about 500-fold lower than the dose used in patients. Nontargeted IFNgamma induced little or no effects over a range of 0.003 to 250 microg/kg. Studies on the mechanism of action showed that low doses of targeted IFNgamma could activate tumor necrosis factor (TNF)-dependent antitumor mechanisms, whereas high doses of either targeted or nontargeted IFNgamma induced soluble TNF-receptor shedding in circulation, a known counterregulatory mechanism of TNF activity. These findings suggest that antitumor activity and counterregulatory mechanisms could be uncoupled by tumor vascular targeting with extremely low doses of IFNgamma.

Aminopeptidase N/CD13 regulates the fetal liver microenvironment of hematopoiesis

Fetal liver (FL) hematopoiesis is thought to be important for expanding the cell number during ontogeny. In order to investigate the cellular interaction molecules among FL stromal and hematopoietic cells, we established a monoclonal antibody, Ndk-10, that reacts with FL stromal cells but not with dish non-adherent cells. When Ndk-10 was added to an FL stromal and hematopoietic cell-coculture, it inhibited the survival of c-kit+ cells. The inhibitory activity of Ndk-10 was also observed in the fetal liver organ culture. The Ndk-10 recognized a 150 kD molecule in the adherent cells of FL and kidney, and the N-terminal amino acid sequence was identical to that of mouse aminopeptidase N/CD13. The peptidase activity of CD13 was inhibited by Ndk-10, and addition of its specific inhibitor resulted in the same inhibitory activity as Ndk-10. We propose that aminopeptidase N/CD13 is a critical molecule that regulates the survival of c-kit+ cells in the FL microenvironment.

Major histocompatibility class II molecules prevent destructive processing of exogenous peptides at the cell surface of macrophages for presentation to CD4 T cells

We studied factors affecting major histocompatibility complex class II (MHC-II)-restricted presentation of exogenous peptides at the surface of macrophages. We have previously shown that peptide presentation is modulated by surface-associated proteolytic enzymes, and in this report the role of the binding of MHC-II molecules in preventing proteolysis of exogenous synthetic peptides was addressed. Two peptides containing CD4 T-cell epitopes were incubated with fixed macrophages expressing binding and non-binding MHC-II, and supernatants were analysed by high-performance liquid chromatography and mass spectrometry to monitor peptide degradation. The proportion of full-length peptides that were degraded and the number of peptide fragments increased when non-binding macrophages were used, leading to reduction in peptide presentation. When MHC-II molecules expressed on the surface of fixed macrophages were blocked with monoclonal antibody and incubated with peptides and the supernatants were transferred to fixed macrophages, a significant reduction in peptide presentation was observed. Peptide presentation was up-regulated at pH 5.5 compared to neutral pH, and the latter was found to be the pH optimum of the proteolytic activity of the surface enzymes involved in the degradation of exogenous peptides and proteins. The data suggest that MHC-II alleles that bind peptides protect them from degradation at the antigen-presenting cell surface for presentation to CD4 T cells and we argue that this mechanism could be particularly pronounced at sites of inflammation.

Induction of CD13 on T-lymphocytes by adhesive interaction with gingival fibroblasts

Lymphocytes in peripheral blood do not express CD13 (aminopeptidase N), a membrane alanyl metallopeptidase. However, it has been demonstrated that locally infiltrated lymphocytes in chronic inflammatory sites can be CD13-positive, and possible involvement of stromal cell adherence in the induction of CD13 has been suggested. In this study, we examined whether T-lymphocyte/gingival-fibroblast interaction can activate T-lymphocytes to express CD13. CD13 expression was induced on PMA-activated T-lymphocytes only when they adhered directly to human gingival fibroblasts (HGF) at 2 hrs after the co-culture began, while an increase in the enzyme activity of CD13 was also confirmed in activated T-lymphocytes that had been co-cultured with HGF. Furthermore, CD13-positive T-lymphocytes were detected in inflamed gingival tissues in vivo. Analysis of these results indicates that direct interaction with HGF is essential for the induction of CD13 expression on T-lymphocytes that was also observed in periodontitis lesions.

The streptococcal exotoxin streptolysin O activates mast cells to produce tumor necrosis factor alpha by p38 mitogen-activated protein kinase- and protein kinase C-dependent pathways

Streptolysin O (SLO), a major virulence factor of pyogenic streptococci, binds to cholesterol in the membranes of eukaryotic cells and oligomerizes to form large transmembrane pores. While high toxin doses are rapidly cytocidal, low doses are tolerated because a limited number of lesions can be resealed. Here, we report that at sublethal doses, SLO activates primary murine bone marrow-derived mast cells to degranulate and to rapidly induce or enhance the production of several cytokine mRNAs, including tumor necrosis factor alpha (TNF-alpha). Mast cell-derived TNF-alpha plays an important protective role in murine models of acute inflammation, and the production of this cytokine was analyzed in more detail. Release of biologically active TNF-alpha peaked approximately 4 h after stimulation with SLO. Production of TNF-alpha was blunted upon depletion of protein kinase C by pretreatment of the cells with phorbol-12 myristate-13 acetate. Transient permeabilization of mast cells with SLO also led to the activation of the stress-activated protein kinases p38 mitogen-activated protein (MAP) kinase and c-jun N-terminal kinase (JNK), and inhibition of p38 MAP kinase markedly reduced production of TNF-alpha. In contrast, secretion of preformed granule constituents triggered by membrane permeabilization was not dependent on p38 MAP kinase or on protein kinase C. Thus, transcriptional activation of mast cells following transient permeabilization might contribute to host defense against infections via the beneficial effects of TNF-alpha. However, hyperstimulation of mast cells might also lead to overproduction of TNF-alpha, which would then promote the development of toxic streptococcal syndromes.

CD13/aminopeptidase N in collagen vascular diseases

To determine the significance of CD13/aminopeptidase N in collagen vascular diseases (CVD), we examined its activity and expression in sera and disease sites of patients with CVD. Significantly higher aminopeptidase activity was detected in bronchoalveolar lavage fluid from patients with interstitial lung diseases due to rheumatoid arthritis (RA), polymyositis/dermatomyositis (PM/DM), systemic sclerosis (SSc), and Sjögren's syndrome than from control subjects. Increased aminopeptidase activity and increased expression of CD13/aminopeptidase N protein were found in alveolar macrophages from CVD patients with interstitial lung diseases. Significantly higher aminopeptidase activity was detected in pleural effusions from patients with systemic lupus erythematosus (SLE) than in transudate effusions. The mean aminopeptidase activity in synovial fluids from RA patients was significantly higher than from patients with osteoarthritis. The mean value of serum aminopeptidase activity was significantly higher in patients with SLE, RA, SSc, and PM/DM than in normal subjects. This study suggests that the activity of CD13/aminopeptidase N, locally produced in the disease site, is a useful marker for CVD and that CD13/aminopeptidase N may have an important role in the pathogenesis of CVD.

Transcriptional regulation of cytosol and membrane alanyl-aminopeptidase in human T cell subsets

Aminopeptidase inhibitors strongly affect the proliferation and function of immune cells in man and animals and are promising agents for the pharmacological treatment of inflammatory or autoimmune diseases. Membrane alanyl-aminopeptidase (mAAP) has been considered as the major target of these anti-inflammatory aminopeptidase inhibitors. Recent evidence also points to a role of the cytosol alanyl-aminopeptidase (cAAP) in the immune response. In this study we used quantitative RT-PCR to determine the mRNA expression of both cAAP and mAAP in resting and activated peripheral T cells and also in CD4+, CD8+, Th1, Th2 and Treg (CD4+ CD25+) subpopulations. Both mAAP and cAAP mRNAs were expressed in all cell types investigated, and in response to activation their expression appeared to be upregulated in CD8+ cells, but downregulated in Treg cells. In CD4+ cells, mAAP and cAAP mRNAs were affected in opposite ways in response to activation. The cAAP-specific inhibitor, PAQ-22, did not affect either cAAP or mAAP expression in activated CD4+ or CD8+ cells, whereas in activated Treg cells it markedly upregulated the mRNA levels of both aminopeptidases. The non-discriminatory inhibitor, phebestin, significantly increased the amount of mAAP and cAAP mRNA in CD4+ and that of cAAP in Treg cells.

Human coronavirus 229E: receptor binding domain and neutralization by soluble receptor at 37 degrees C

Truncated human coronavirus HCoV-229E spike glycoproteins containing amino acids 407 to 547 bound to purified, soluble virus receptor, human aminopeptidase N (hAPN). Soluble hAPN neutralized the infectivity of HCoV-229E virions at 37 degrees C, but not 4 degrees C. Binding of hAPN may therefore trigger conformational changes in the viral spike protein at 37 degrees C that facilitate virus entry.

CD13/aminopeptidase N-induced lymphocyte involvement in inflamed joints of patients with rheumatoid arthritis

OBJECTIVE

We previously showed that CD13/aminopeptidase N (EC 3.4.11.2) induces chemotactic migration of T lymphocytes by its enzymatic activity. In this study, we examined the role of CD13/aminopeptidase N in lymphocyte involvement in rheumatoid arthritis (RA).

METHODS

Synovial fluids were obtained from 27 RA patients and 6 osteoarthritis (OA) patients. Synovial tissue specimens were obtained from 3 RA patients and 3 OA patients. Protease activity of aminopeptidase in synovial fluids and synovial fibroblasts was assayed fluorometrically using the specific substrate. Expression of CD13/aminopeptidase N in synovial fibroblasts was determined by flow cytometry analyses, Western blotting, and reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

The mean value of aminopeptidase activity in synovial fluid samples from RA patients was significantly higher than that in samples from OA patients. Increased enzymatic activity of aminopeptidase was detected on synovial fibroblasts from RA patients compared with those from OA patients. Flow cytometry showed that the expression of CD13/aminopeptidase N on synovial fibroblasts from RA patients was higher than the expression on synovial fibroblasts from OA patients, and Western blots and RT-PCR showed that synovial fibroblasts from RA patients contained a greater amount of CD13/aminopeptidase N. The activity of CD13/aminopeptidase N correlated significantly with lymphocyte counts in synovial fluids from RA patients. Synovial fluids from RA patients in which high aminopeptidase activity was detected contained considerable chemotactic activity for lymphocytes, and bestatin, a specific inhibitor of aminopeptidases, partially inhibited the chemotactic activity.

CONCLUSION

CD13/aminopeptidase N may participate in the mechanism of lymphocyte involvement in inflamed joints of RA patients as a lymphocyte chemoattractant.

Characterization of a monoclonal antibody specific for a novel primate cell surface marker with distinct biochemical properties on human erythroleukemia and myeloid cell lines

A hybridoma, CSC-1, which secretes monoclonal antibody (MAb) specific for a cell surface molecule on African green monkey kidney cell line, BGMK, was isolated and characterized. The cell surface molecule recognized by CSC-1 is widely expressed on a variety of human cell lines. Among the hematopoietic cell lines examined, the CSC-1 marker seems to be preferentially expressed by lymphoid cell lines (e.g., Raji, CEM-SS, Jurkat, and MOLT-3). Although CSC-1 also recognizes some uncommitted myeloid and erythroleukemia cell lines (e.g., U-937 and K562), the CSC-1 marker expression on these cell lines is subjected to PMA-induced down-regulation. In addition, the PMA-induced cell surface down-regulation of the CSC-1 marker required more than 24 h. Proteolytic analysis shows that the CSC-1 marker can be categorized into proteinase K-resistant and-sensitive phenotypes. Furthermore, the CSC-1 marker exhibits a slow cell surface turnover rate after proteinase K treatment. Our data suggest that the CSC-1 cell surface molecule might be useful as a megakaryocytic or monocytic differentiation marker.

IL-9 and IL-13 production by activated mast cells is strongly enhanced in the presence of lipopolysaccharide: NF-kappa B is decisively involved in the expression of IL-9

Mast cells, due to their ability to produce a large panel of mediators and cytokines, participate in a variety of processes in adaptive and innate immunity. Herein we report that in primary murine bone marrow-derived mast cells activated with ionomycin or IgE-Ag the bacterial endotoxin LPS strongly enhances the expression of IL-9 and IL-13, but not IL-4. This costimulatory effect of LPS is absent in activated mast cells derived from the LPS-hyporesponsive mouse strain BALB/c-LPS(d), although in these cells the proinflammatory cytokine IL-1 can still substitute for LPS. The enhanced production of mast cell-derived IL-13 in the presence of IL-1 is a novel observation. Coactivation of mast cells with LPS leads to a synergistic activation of NF-kappa B, which is shown by an NF-kappa B-driven reporter gene construct. In the presence of an inhibitor of NF-kappa B activation, the production of IL-9 is strongly decreased, whereas the expression of IL-13 is hardly reduced, and that of IL-4 is not affected at all. NF-kappa B drives the expression of IL-9 via three NF-kappa B binding sites within the IL-9 promoter, which we characterize using gel shift analyses and reporter gene assays. In the light of recent reports that strongly support critical roles for IL-9 and IL-13 in allergic lung inflammation, our results emphasize the potential clinical importance of LPS as an enhancer of mast cell-derived IL-9 and IL-13 production in the course of inflammatory reactions and allergic diseases.

Inhibition of aminopeptidase N (AP-N) and urokinase-type plasminogen activator (uPA) by zinc suppresses the invasion activity in human urological cancer cells

Zinc is an essential heavy metal and is more abundant in human prostate and kidney than in other tissues. The effects of zinc on the invasion activity of human prostate and renal cancer cell lines, PC-3, LNCaP and SKRC-1, were investigated in vitro using a Transwell cell-culture chamber and were compared with specific protease inhibitors for MMPs, uPA and AP-N, respectively. The invasion activity of PC-3 cells was effectively suppressed by zinc and by all protease inhibitors in a dose-dependent manner. The invasion activity of LNCaP cells was almost unaffected by these inhibitors. In SKRC-1 cells, the invasion activity was strongly suppressed by MP03, although a moderate inhibition by zinc and bestatin was observed. The purified AP-N activity was strongly inhibited by zinc at a concentration similar to that suppressing the invasion activity of PC-3 cells and this inhibition by zinc was apparently competitive. Although the purified uPA activity was also inhibited by zinc, this inhibition was uncompetitive. AP-N was expressed abundantly on the membrane fraction of PC-3 cells among these cells tested, while its expression on the membrane fraction of SKRC-1 cells was weaker than that of PC-3 cells. The expression of uPA was also highest on the membrane fraction of PC-3 cells. These results suggest that AP-N and uPA may be involved in the invasion of human prostate cancer cells and that zinc probably participates in the invasion and metastasis of cancer cells through the regulation of the enzymatic activity of AP-N and uPA in human cancerous prostate.

Enhancement of tumor necrosis factor alpha antitumor immunotherapeutic properties by targeted delivery to aminopeptidase N (CD13)

The clinical use of tumor necrosis factor alpha (TNF) as an anticancer drug is limited to local treatments because of its dose-limiting systemic toxicity. We show here that murine TNF fused with CNGRC peptide (NGR-TNF), an aminopeptidase N (CD13) ligand that targets activated blood vessels in tumors, is 12-15 times more efficient than murine TNF in decreasing the tumor burden in lymphoma and melanoma animal models, whereas its toxicity is similar. Similarly, human NGR-TNF induced stronger antitumor effects than human TNF, even with 30 times lower doses. Coadministration of murine NGR-TNF with a CNGRC peptide or an anti-CD13 antibody markedly decreased its antitumor effects. Tumor regression, induced by doses of murine NGR-TNF lower than the LD50, was accompanied by protective immunity. In contrast, no cure was induced by TNF at any dose. These results suggest that targeted delivery of TNF to CD13 may enhance its immunotherapeutic properties. Moreover, these findings reveal the potential of tumor homing peptides to generate a new class of recombinant cytokines that compared to immunocytokines have a simpler structure, could be easier to produce and are potentially less immunogenic.

Novel molecular mechanisms of dendritic cell-induced T cell activation

In this study we have re-examined the molecular mechanisms involved in activation of T cells by dendritic cells (DC). Human peripheral blood DC (PBDC) were derived by 2 h adhesion followed by 7 day culture in a combination of granulocyte macrophage colony stimulating factor and IL-4, and depletion of residual T and B cells. These PBDC were used to induce autologous T cell proliferation in a CD3-dependent response, and antibodies against CD11a/18 and CD86 were used as control inhibitors of accessory function. Antibodies against five of the cell surface molecules that we have recently identified on the surface of DC, CD13, CD87, CD98, CD147 and CD148, and an antibody which recognizes a molecule that has not as yet been identified, all inhibited the CD3-induced T cell proliferation. These findings were observed not only when antibodies were present throughout the culture, but also when they were prepulsed on to the surface of the DC, suggesting the inhibition was mediated via the antigen-presenting cells rather than the T cell. The same set of antibodies also inhibited an allospecific mixed lymphocyte reaction, confirming that the inhibitory effect was not dependent on the use of a CD3 antibody as the stimulating agent. All the antibodies of known specificity inhibited both CD4 and CD8 T cells equally. Unlike CD87, CD98 and CD147 antibodies, which inhibited activation of both CD45RA (naive) T cells and CD45RO (memory) T cells, CD13 and CD148 appeared to be involved in activation of naive cells only. The molecules identified in this study have not previously been demonstrated to play a role as accessory molecules on DC, the cells that are pivotal for immune induction. Therefore they may provide new potential targets for modulation of the immune response at the APC level.

Inhibition of alanyl-aminopeptidase suppresses the activation-dependent induction of glycogen synthase kinase-3beta (GSK-3beta) in human T cells

Inhibition of alanyl-aminopeptidase (APN, CD13) gene expression or enzymatic activity compromises T cell proliferation and function. Molecular mechanisms mediating these effects are not known as yet. Recently, we found the expression of the proto-oncogen Wnt-5a to be strongly affected by APN-inhibition. Wnt-5a and other members of the Wnt family of secreted factors are implicated in cell growth and differentiation. Here, we analyzed by quantitative RT-PCR and immunoblotting the expression in mitogen-activated T cells of a major constituent of the Wnt-5a pathway, glycogen synthase kinase-3beta (GSK-3beta). T cell activation by phytohaemagglutinin or pokeweed mitogen results in a strong increase of GSK-3beta mRNA amounts. At the protein level, we observed an up-regulation of both GSK-3beta and phosphorylated GSK-3beta. This induction-dependent increase of GSK-3beta is markedly reduced in response to inhibitors of alanyl-aminopeptidase, actinonin, leuhistin, and RB3014. These findings may provide a rational for the growth inhibition resulting from a diminished expression or activity of alanyl aminopeptidase.

CD13/aminopeptidase N, a novel chemoattractant for T lymphocytes in pulmonary sarcoidosis

CD13/aminopeptidase N (E.C.3.4.11.2) is an ectoenzyme located in the outer membrane of a variety of cells. Because aminopeptidase expression was shown to be upregulated by a Th1-related cytokine, IFN-gamma, we examined here the significance of CD13/aminopeptidase N in pulmonary sarcoidosis. The activity of aminopeptidase in bronchoalveolar lavage fluid (BALF) was significantly higher in patients with sarcoidosis than in normal volunteers (NV) and control patients (CP). The activity significantly correlated with lymphocyte percentages and the ratio of CD4+ to CD8+ T lymphocytes in the BALF, and was higher in patients with sarcoidosis with parenchymal involvement than in those without the involvement. CD13/aminopeptidase N protein, which has a molecular mass of approximately 150 kD, was detectable in alveolar macrophages (AM) from patients with sarcoidosis at higher levels than in those from NV. CD13/aminopeptidase N induced in vitro chemotactic migration of human lymphocytes in a concentration range of 10(-)(5) to 10(-)(1) U/ml. The chemotactic activity was greater for CD4+ T lymphocytes than for CD8+ T lymphocytes. The enzymatic activity of CD13/aminopeptidase N was responsible for the chemotactic activity because bestatin, an inhibitor of CD13/aminopeptidase N, abolished the chemotactic activity. Higher chemotactic activity for lymphocytes was detected in the BALF from patients with sarcoidosis than in that from NV, and the activity was significantly decreased by treatment with bestatin. This study indicates that CD13/ aminopeptidase N expressed in AM may have a role in T-lymphocyte involvement in the sarcoid lung and the pathogenesis of alveolitis in this disorder.

Equine macrophage identification with an antibody (Ki-M6) to human CD68 and a new monoclonal antibody (JB10)

Monoclonal antibodies (mAbs) recognizing equine macrophages are scarce. The present study compared the immunocytochemical staining of various equine tissues (lymphoid tissue, lung, liver, small intestine, skin and blood leucocytes) by an antibody, Ki-M6, which detects CD68 in human macrophages and dendritic cells, and by a new anti-equine mAb, JB10, with staining produced by two previously described anti-equine macrophage mAbs, CZ2.2 and CZ3.3. Ki-M6 was shown to identify equine macrophages, which had a distribution different from those identified by CZ2.2 and CZ3.3. JB10 identified equine macrophages with a distribution similar to those identified by Ki-M6, but additionally bound to polymorphonuclear leucocytes. Flow cytometry of peripheral blood leucocyte subpopulations and tissue immunocytochemistry were used to compare staining by JB10 with that of CZ2.2 and CVS19; the latter identifies the myeloid antigen, EqCD13, found on polymorphonuclear leucocytes. The staining by JB10 differed from that of both CZ2.2 and CVS19, suggesting that JB10 detects a different molecule. These additional mAbs should prove useful for the future study of new, defined, populations of macrophages in equine immune responses and pathology, and, in the case of Ki-M6 antibody, may make possible an analysis of the structure, distribution and function of the CD68 molecule in the horse.

CD13/N-aminopeptidase is involved in the development of dendritic cells and macrophages from cord blood CD34+ cells

Expression of CD13/N-aminopeptidase may reflect cell activation and growth. We examined its role regarding cell growth in cultures of cord blood CD34+ cells with stem cell factor/Flt-3 ligand/granulocyte-macrophage colony-stimulating factor/tumor necrosis factor-. Indeed, 82% ± 6% of cells from culture day 5 were CD13hi, 25% ± 8% of which were still Lin−. About 50% of CD13hiLin− cells, which comprise progenitors of dendritic cells (DC), monocytes/macrophages and granulocytes, and 30% of CD13loLin− cells were CD34+. Sorted CD34+CD13hiLin− cells, cultured further for 7 days with the same cytokines, expanded 31-fold and CD34-CD13hiLin− cells 7-fold, but CD34+CD13loLin− and CD34−CD13loLin− cells did not grow. Thus, cell growth correlated with CD13 expression, all the more so that cells were CD34+. Actinonin, the most potent N-aminopeptidase inhibitor, was used to engage CD13 on sorted CD13hiLin− cells and on culture day-7 bulk cells. In both cases, this resulted in reversible cell growth arrest, with 30% to 60% fewer cells in the G2/S-M phase than in controls. Interestingly, similar effects were noted with CD13 monoclonal antibody TÜK1, which does not inhibit N-aminopeptidase activity, but not with N-aminopeptidase-blocking antibodies WM15 and F23. All cycling cells appeared susceptible to actinonin, which induced cell apoptosis at the same time as Bcl-2 was downregulated and caspase-3 activity increased, but finally percentages and yields of DC and macrophage precursors were affected more than those of granulocytic cells. Thus, through engagement of N-aminopeptidase enzymatic site but possibly also of an independent determinant, CD13 plays a role in the growth of DC/macrophage progenitors and precursors.

Secretion of human meprin from intestinal epithelial cells depends on differential expression of the alpha and beta subunits

Human meprin (N-benzoyl-l-tyrosyl-p-aminobenzoic acid hydrolase, EC 3.4.24.18), an astacin-type metalloprotease, is expressed by intestinal epithelial cells as a dimeric protein complex of alpha and beta subunits. In transfected cells, intracellular proteolytic removal of the membrane anchor from the alpha subunit results in its secretion, while the beta subunit and alpha/beta heterodimers are retained at the cell membrane. We investigated the consequence of differential intracellular processing of alpha and beta subunits in the human small and large intestine using subunit-specific immunohistochemistry, in situ hybridization and biosynthetic studies in organ culture. In the ileum, both subunits localize to the brush-border membrane of villus enterocytes. In contrast, the beta subunit is not expressed in the colon, which leads to the secretion of the alpha subunit. We conclude that differential expression of meprin alpha and beta subunits is a unique means of targeting the proteolytic activity of the alpha subunit either to the brush-border membrane in the ileum or to the lumen in the colon, suggesting dual functions of cell-associated and luminal meprin. Meprin alpha and beta subunits are also coexpressed in distinct lamina propria leukocytes, suggesting an additional role for this protease in leukocyte function in the intestinal mucosa.

Inhibition of alanyl aminopeptidase induces MAP-kinase p42/ERK2 in the human T cell line KARPAS-299

Inhibition of alanyl aminopeptidase (EC 3.4.11.2, aminopeptidase N, CD13) expression, or activity compromise cell proliferation in a number of cell systems [1, 2, 3, 4, 5, 6]. The underlying mechanisms and the molecular components involved have not been identified as yet. In this study we show that inhibition of alanyl aminopeptidase enzymatic activity decreases the proliferation rate of the CD13-positive T cell line Karpas-299. By using the ATLAS cDNA expression array (Clontech) we identified the p42/ERK2 MAP kinase as one downstream target of probestin, a potent inhibitor of alanyl aminopeptidase. Probestin and another specific aminopeptidase inhibitor, actinonin, in addition to their capability of inducing erk-2 mRNA levels, significantly increase p42 phosphorylation state. This is the first report on signal transduction components possibly mediating the growth-modulatory effects of alanyl aminopeptidase inhibitors.

Human cytomegalovirus infection downregulates expression of the cellular aminopeptidases CD10 and CD13

During the course of a productive infection, human cytomegalovirus (HCMV) has a sophisticated relationship with its host cell. An increasing number of virus-encoded genes are being identified which act specifically to usurp or modulate functions in the host cell associated with transcriptional control, cell signalling, and protein synthesis. While HCMV infection is associated with a general upregulation of cellular gene expression, the expression a small subset of cellular proteins, including the MHC-1 heavy chain and fibronectin, is downregulated. This study now identifies two additional cellular proteins, aminopeptidase N (CD13) and neutral endopeptidase (CD10), that are downregulated during HCMV infection. While aminopeptidase N and neutral endopeptidase exhibit no significant sequence homology, both are expressed on the cell surface and have very similar enzymatic properties. HCMV infection was associated with reduced surface expression and enzyme activity of CD13 and CD10, an apparent decrease in the rate of synthesis of both proteins in metabolic-labelling experiments, and inhibited glycosylation of the nascent CD13 and CD10 polypeptide chains that were synthesized. Levels of CD10 poly A+ RNA were suppressed efficiently at all stages of virus infection; however, the reduction in CD13 poly A+ RNA levels was much less pronounced. This differential effect suggests that HCMV may be downregulating expression of CD10 and CD13 by independent mechanisms. Indeed, treatment of cells with an inhibitor of viral DNA synthesis blocks downregulation of CD13, whilst downregulation of CD10 is unaffected. While it is not yet clear what advantage is bestowed on the virus by downregulating expression of CD13 and CD10, aminopeptidases are known to have a role in peptide processing in both the MHC class I the MHC class II antigen presentation pathways.

Heterogeneity of Mouse Spleen Dendritic Cells: In Vivo Phagocytic Activity, Expression of Macrophage Markers, and Subpopulation Turnover

In the normal mouse spleen, two distinct populations of dendritic cells (DC) are present that differ in microanatomical location. The major population of marginal DC is found in the “marginal zone bridging channels” and extends into the red pulp. The interdigitating cells (IDC) are localized in the T cell areas in the white pulp. The aim of the present study was to characterize these two splenic DC populations with regard to their phenotype, in vivo phagocytic function, and turnover. Both marginal DC and IDC are CD11c+ and CD13+, but only IDC are NLDC-145+ and CD8α+. Notably, both populations, when freshly isolated, express the macrophage markers F4/80, BM8, and Mac-1. To study the phagocytic capacity of these cells, we employed the macrophage “suicide” technique by injecting liposomes loaded with clodronate i.v. Marginal DC, but not IDC, were eliminated by this treatment. Phagocytosis of DiI-labeled liposomes by DC confirmed this finding. The two DC populations differed significantly with regard to their turnover rates, as studied in a transgenic mouse model of conditional depletion of DC populations with high turnover. In these mice, marginal DC were completely eliminated, but the IDC population remained virtually intact. From these data we conclude that the marginal DC population has a high turnover, in contrast to the IDC population. Taken together, the present results indicate that marginal DC and IDC represent two essentially distinct populations of DC in the mouse spleen. They differ not only in location, but also in phenotype, phagocytic ability, and turnover.

Rapid mitogen-induced aminopeptidase N surface expression in human T cells is dominated by mechanisms independent of de novo protein biosynthesis

The membrane bound metalloprotease aminopeptidase N (APN, CD13, EC 3.4.11.2) is a well established marker of normal and malignant cells of the myelo-monocytic lineage. It is also expressed by leukaemic blasts of a small group of patients suffering from acute or chronic lymphoid leukaemia. Recently, the expression of the APN gene in T cell lines as well as the induction of APN gene and surface expression in human peripheral T cells by mitogenic activation have been demonstrated. Here, by means of cytofluorimetric analysis evidence is provided, that the induction of APN surface expression is partially resistent to the action of the inhibitors of protein biosynthesis, puromycin and cycloheximide, and is not prevented by tunicamycin, an inhibitor of glycosylation. These data suggest that the rapid mitogen-induced surface expression of APN, detectable 20 hours after stimulation is dominated by mechanisms not dependent on de novo protein biosynthesis or glycosylation. As shown by simultaneous analyses, the inhibitors used did also differently modify the induction of surface expression of other inducible glycosylated leukocyte surface antigens, namely CD25, CD69 and CD95.

The main neutral aminopeptidase activity of human lymphoid tumour cell lines does not originate from the aminopeptidase N-(APN; CD13) gene

Lymphocytes and related cell lines are predominantly CD13-negative, however, there are reports describing neutral aminopeptidase activity in or on these cells. The aim of this study was to answer the question, whether this activity originates from APN-gene expression. The total cellular activities (Ala-pNA hydrolysis) of lymphoid cell lines are up to 15 times higher than that of normal lymphocytes. Despite weak or lacking CD13 surface expression all lymphoid cell lines tested contain APNmRNA as quantified by competitive RT-PCR as well as low enzymatic activity in their particulate fractions. By isoelectric focusing two enzyme species with isoelectric points of 5.4 or between 3.5 to 4.8, respectively, were detected. To investigate whether these activities result from APN-gene we established transfectants lacking cellular APN expression of the CD13-positive histiocytic cell line U937 and the CD13-negative T-cell line H9. Studies on these transfectants proved (I) that the main neutral aminopeptidase activity expressed in lymphoid cells is definitively not related to APN and (II) that APN is also expressed in lymphoid cells, although on a low level only.

Induction of the membrane alanyl aminopeptidase gene and surface expression in human T-cells by mitogenic activation

The metal-dependent membrane alanyl aminopeptidase (amino-peptidase N, APN, CD13; EC 3.4.11.2) is a well-established marker of normal and malignant cells of the myelo-monocytic lineage. It is also expressed by leukaemic blasts of a small group of patients suffering from acute or chronic lymphoid leukaemia. CD13-specific monoclonal antibodies do not bind to the surface of normal B lymphocytes, and APN mRNA was not detectable by Northern analysis in normal lymphocytes or in T-cell lines. Recently the expression of the APN gene in T-cell lines as well as the ability of these cells to cleave chromogenic substrates preferred by APN have been demonstrated [Lendeckel, Wex, Kähne, Frank, Reinhold and Ansorge (1994) Cell. Immunol. 153, 214-226]. Here, by means of dot-blot hybridization and RNase protection assay, evidence is provided that human peripheral T-cells as well as derived cell lines contain significant amounts of APN mRNA, comparable to that in the promyeloic cell line U937, and that mitogenic activation of peripheral human T-cells leads to a more than 4-fold increase in their APN mRNA content. In the course of activation, T-cells increase their total alanine p-nitroanilide-hydrolysing activity to approx. 7-fold that of resting cells. Furthermore these cells become immunoreactive towards CD13 to a significant extent (up to 51%) as shown by surface staining and confirmed by activity staining and immunostaining after isoelectric focusing (pI of T-cell APN = 4.6). In addition it is demonstrated by fluorescence microscopy that viable, activated T-cells effectively cleave the fluorogenic aminopeptidase substrate bis-glycyl-rhodamine 110 and that the corresponding aminopeptidase activity is associated with the cell surface. We show that specific inhibitors of APN, probestin and actinonin, strongly decrease DNA synthesis in phytohaemagglutinin (PHA)-stimulated T-cells. In summary, evidence is presented that in the course of mitogenic activation human peripheral T-cells increase the expression of APN both at the transcriptional level and at the cell surface. This has been demonstrated both at the APN mRNA level and at the protein level with respect to aminopeptidase enzymic activity and CD13 immunoreactivity.

T cell responses affected by aminopeptidase N (CD13)-mediated trimming of major histocompatibility complex class II-bound peptides

Endocytosed protein antigens are believed to be fragmented in what appears to be a balance between proteolysis and MHC-mediated epitope protection, and the resulting peptide-MHC complexes are transported to the surface of the antigen-presenting cells (APC) and presented to T cells. The events that lead to antigenic peptide generation and the compartments where antigen processing takes place remains somewhat enigmatic. The importance of intracellular antigen processing has been well established; however, it is unclear whether additional processing occurs at the APC surface. To follow antigen processing, we have identified a pair of T cell hybridomas that recognize a long vs. a short version of the same epitope. We have used prefixed APC and various protease inhibitors to demonstrate that the APC surface has a considerable potential for antigen processing. Specific antibodies further identified the exopeptidase Aminopeptidase N (APN, CD13) as one of the enzymes involved in the observed cell-surface antigen processing. The NH2-terminal end of the longer peptide could, even while bound to major histocompatibility complex (MHC) class II molecules, be digested by APN with dramatic consequences for T cell antigen recognition. This could be demonstrated both in cell-free systems using purified reagents and in cellular systems. Thus, MHC class II and APN may act in concert to generate the final T cell epitopes.

Activity of neutral endopeptidase and aminopeptidase N in mouse thymic stromal cells which bind double-positive thymocytes

The activity of two peptidases was determined in immortalized lines of thymic stromal cells. A line of total stromal cells (T-TG-St) was grown from transgenic mouse expressing temperature-sensitive SV40 T antigen under the control of the regulatory elements of the mouse major histocompatibility complex class I gene. From these cells we isolated a subset (DP-TG-St) that binds thymocytes which are mainly CD4+8+. We also assayed a clone of fetal thymic epithelial cells (BA/10) that binds CD4+8+ thymocytes. Both lines of double -positive cell-binding stroma exhibited strong activity of two peptidases, neutral endopeptidase (NEP; EC 3.4.24.11) and aminopeptidase N (APN; EC 3.4.11.2). In contrast, the activity of both enzymes was very low in the total thymic stromal line. Use of the specific inhibitors confirmed that these two enzymes were responsible for the activity observed but also suggested the presence of additional unidentified aminopeptidase(s) in the same stromal cells. The high activity of the two peptidases on stromal cells that bind thymocytes at the double-positive stage raises the possibility that they might contribute to the microenvironment of the developing thymocytes.

Fine chemical modifications at N- and C-termini enhance peptide presentation to T cells by increasing the lifespan of both free and MHC-complexed peptides

We investigated the effect of modifying the N- and/or C-termini of the snake toxin peptide 24-36 on its presentation to T cells. Acetylation at the N-terminus as well as amidation at the C-terminus enhanced the capacity of the peptide to activate T cells. Simultaneous modifications further increased the stimulating activity, the peptide becoming approximately 100-fold more potent than the unmodified peptide. Clearly, the introduced modifications increased the lifetime of the peptide free in solution, by decreasing its proteolytic degradation, during the T cell stimulation assays. Paradoxically, however, at similar concentrations of free peptides, the modified ones, especially those having an acetylated N-terminus, were much more active than the unmodified peptide, irrespective of the experimental conditions. These observations suggested that components other than protection from proteolytic degradation should be associated with the higher stimulating activities of the modified peptides. Accordingly, chasing experiments with APC revealed that acetylation at N-terminus caused a higher persistence of the peptides at APC surface. Together, our data indicate that (i) the T cell stimulating capacity of a peptide is associated with its lifespans in the free and MHC II bound states; and (ii) these lifespans can be greatly enhanced by introducing fine chemical modifications at N- and C-termini. These data may have some implications in designing more potent peptidic immunomodulators.

Quantification of aminopeptidase N mRNA in T cells by competitive PCR

The aminopeptidase N (CD13, EC 3.4.11.2) is a well-characterized surface molecule expressed in a variety of cell types and species. Recent data indicate an expression of the APN mRNA and the corresponding aminopeptidase activity in human peripheral T cells and related cell lines as well. Here, the sensitive method of competitive PCR was used to quantify low amounts of APN mRNA in T cell lines. An APN cDNA fragment enshortened by a deletion of 87 bp was used as an internal APN-specific standard. The myelo-monocytic cell line U937 and the lymphoid T cell lines HuT78 and H9 contain 2.3 x 10(7), 5.9 x 10(6) and 5.6 x 10(6) copies/micrograms total RNA, corresponding to 160, 70 and 50 copies/cell, respectively. These data have been confirmed by determination of the APN activity, that represents a fraction only of the total cellular neutral aminopeptidase activity in hematopoetic cells. In the case of the CD13-positive cell line U937, approximately 60-70% of the total neutral aminopeptidase activity could be attributed to APN. In contrast, only a minor fraction (5-20%) of the cellular neutral aminopeptidase activity in the T cell lines H9 and HuT78 represents APN. The results suggest that APN gene expression within the hematopoetic system is not restricted to myelo-monocytic cells, instead a low APN expression may be a common feature of lymphocytes, at least of T cells, too.

Expression of aminopeptidase N/CD13 in tumour-infiltrating lymphocytes from human renal cell carcinoma

We have previously demonstrated the expression of aminopeptidase N (APN, CD13) on synovial T cells from patients with different forms of arthritis. T cells of peripheral blood and serous body fluids are CD13-negative but can be stimulated to express CD13 after activation, e.g., with Con A. In the present report, double-labelling and flow cytometry analyses were performed to characterize the phenotype of tumour-infiltrating lymphocytes (TIL). A large panel of antibodies specific for different activation-associated molecules on T cells was used. In contrast to TIL of lung cancer, TIL of renal cell carcinoma (RCC) consisted of significantly higher percentages of T cells expressing CD13, dipeptidylpeptidase N (DPIV, CD26) and HLA-DR, whereas T cells of lung cancer expressed more CD25, CD69 and CD54/ICAM1. No differences could be found in the expression of CD45RO, CD49a/VLA-1 and CD62L/L-selectin. Our results demonstrate that T cells in RCC and lung cancer differ in their phenotype, especially with respect to surface aminopeptidases. Investigations into the function of APN on T cells could be of help in gaining deeper insight into tumour defence as well as into general mechanisms of T cell functions.