Intraperitoneal immunization with oligomannose-coated liposome-entrapped soluble leishmanial antigen induces antigen-specific T-helper type immune response in BALB/c mice through uptake by peritoneal macrophages

The present study demonstrates that the intraperitoneal administration of soluble leishmanial antigen (SLA) entrapped in liposomes coated with neoglycolipids containing oligomannose residues (mannopentaose or mannotriose) strongly induces an antigen-specific T-helper type 1 (Th1) immune response in BALB/c mice. In response to in vitro stimulation with SLA, spleen cells from mice that had received oligomannose-coated liposomes encasing SLA (SLA-OML) displayed greater interferon (IFN)-gamma and interleukin (IL)-2 production and lower IL-4 and IL-5 production than spleen cells from mice that had received SLA alone, indicating that the SLA-specific Th1 immune response had predominantly been induced in the mice that had received SLA-OML. After subsequent infection with Leishmania major, mice that had received SLA-OML were effectively protected against the disease, with a predominant production of IFN-gamma. OML were preferentially and rapidly incorporated into peritoneal macrophages, and the transplantation of macrophages containing SLA-OML into the peritoneal cavity also induced protection against L. major infection. Thus, SLA-OML were shown to successfully induce a specific Th1 immune response capable of controlling L. major infection in BALB/c mice through the effective uptake of OML by peritoneal macrophages.

Different role of Apaf-1 in positive selection, negative selection and death by neglect in foetal thymic organ culture

Apoptotic protease-activating factor 1 (Apaf-1) is a component of the apoptosome which is required for the activation of procaspase-9. As Apaf-1 knockout (KO) (Apaf-1-/-) mice die before birth, the role of Apaf-1 during thymic selection was investigated using 5 day foetal thymic organ culture (FTOC) of thymi obtained at gestational day 15. There was a lower ratio of CD4 single-positive (SP) to CD8 SP cells and decreased apoptosis of CD4+CD8+ (DP) thymocytes from Apaf-1-/- mice compared with wild-type. To determine if these defects resulted in increased production of neglected thymocytes, the Apaf-1-/- mice were crossed with the T-cell receptor (TCR)-alpha-chain KO mice. There was no difference in thymocyte development in the thymi of TCR-alpha-/-Apaf-1-/- and TCR-alpha-/-Apaf-1+/+ mice 5 days after FTOC. To determine if Apaf-1 is involved in apoptosis during death by negative or positive selection, FTOC of the thymus of Apaf-1-/- Db/HY TCR-alphabeta transgenic (Tg) mice was carried out. There was decreased apoptosis of the HY clonal-specific M33+ thymocytes and an increased percentage of the autoreactive CD8+M33+ thymocytes in male, but not female Apaf-1-/- Db/HY TCR Tg mice. Our data suggest that Apaf-1 is not involved in positive selection or death by neglect, but may have a partial role in negative selection during early thymic T-cell development.

Liposome-mediated gene therapy using HSV-TK/ganciclovir under the control of human PSA promoter in prostate cancer cells

To more accurately determine the tissue-specific expression of the target gene in prostate cancer cells, we introduced the enhancer element (-4,777 to -3,934; PSAR) and the promoter region (PSAP) of the prostate-specific antigen (PSA) gene. Furthermore, to elucidate the advantages of using liposomes as a gene carrier, we screened more than 20 liposome preparations in this study. The 5' upstream region of PSA gene (PSARPSAP) was conjugated to either the chloramphenicol acetyltransferase (CAT) gene or herpes simplex virus thymidine kinase (TK) gene, and the transfection of these plasmids was carried out using cationic liposomes, DMRIE-C (Gibco) or LipoTAXI (Stratagene). The expression of CAT activity was clearly observed when PSARPSAP-CAT plasmid was transfected into PSA-positive LNCaP cells, whereas no CAT activity was detected in PSA-negative DU145 cells or bladder carcinoma T24 cells. The CAT activity increased after the addition of testosterone. We then evaluated the therapeutic effect of the PSARPSAP-TK plasmid in vitro. When PSARPSAP-TK plasmid was transfected and ganciclovir was added to the medium, the growth of LNCaP cells was inhibited, while no growth inhibition was observed in DU145 cells. Furthermore, this inhibitory effect was observable even when the cells were cultured in a medium supplemented with dialyzed fetal bovine serum. These results suggest that the liposome-mediated transfection of PSARPSAP-TK appears to be a potentially effective approach for selecting the optimal treatment for tumor cells producing PSA even with the low androgen levels seen in patients treated by anti-androgen therapy.

Suicide gene therapy on LNCaP human prostate cancer cells

The efficacy of combination suicide gene therapy was evaluated using a Herpes simplex virus-thymidine kinase/ganciclovir (HSV-TK/GCV) system and an Escherichia coli cytosine deaminase/5-fluorocytosine (CD/5-FC) system on the LNCaP human prostate cancer cell model. Two types of plasmid vectors with the HSV-TK gene were constructed. A constitutive chicken beta-actin promoter drove one and a prostate-specific antigen (PSA) promoter drove the other. Similarly, a pair of plasmids with the CD gene under a cytomegalovirus (CMV) promoter and the PSA promoter was also constructed. LNCaP cells were transfected in vitro with either or both of those plasmids using a cationic lipid reagent. Transfected cells were treated with GCV and/or 5-FC. The percentage of viable LNCaP cells 7 days after treatment with HSV-TK/GCV or CD/5-FC under a constitutive promoter was 40% and 41% of controls, respectively. The cell viability when two suicide genes were combined was 23%. The cell viabilities after four days with PSA promoter-HSV-TK vectors, CD vectors and a combination of both were 79%, 88% and 88%, respectively. Suicide gene therapy using either HSV-TK/GCV, CD/5-FC, or both, was effective in the LNCaP model. An additive effect was observed when the two suicide genes were used together. The PSA promoter did not seem to be effective enough to elicit cytotoxicity under the experimental conditions used here.

A single intradermal administration of soluble leishmanial antigen and plasmid expressing interleukin-12 protects BALB/c mice from Leishmania major infection

In murine leishmaniasis, the induction of the T-helper type 1 (Th1) response contributes to infection resistance, whereas the establishment of the Th2 response makes the mice susceptible to infection. Interleukin-12 (IL-12) plays a pivotal role in the diversification of immune responses to the Th1 type. In this study, we tested whether the co-administration of IL-12 expression plasmid which compose p35 and p40 subunits and soluble leishmanial antigen (SLA) will skew the susceptible BALB/c mice to Th1 response and protect from leishmaniasis. When the mice were intradermally injected with the combination of IL-12 plasmid and SLA 7 days prior to the challenge with 1x10(6) promastigotes of Leishmania major, the local lesions completely healed and the parasite burden in the local lymph nodes significantly decreased. The cured mice attained long-term immunity, and were resistant to any subsequent rechallenge of the lethal dose of the parasite. The protective effect was associated with the development of a Th1 response, as demonstrated by the enhanced level of antigen-specific interferon-gamma (IFN-gamma) and dominant production of IgG2a in the serum. In contrast, the administration of empty plasmid plus SLA or IL-12 plasmid alone failed to protect the disease and shape the Th1 response. Furthermore, the protective efficiency induced by the vaccination was clearly prevented by the injection of either neutralizing anti-IL-12 mAb or anti-IFN-gamma mAb. The IL-12 expression plasmid is thus an effective adjuvant for the elicitation of a protective Th1 response against leishmaniasis and is therefore, considered to be appropriate for vaccinations that require the induction of Th1 type immunity.

Coexpression of the partial androgen receptor enhances the efficacy of prostate-specific antigen promoter-driven suicide gene therapy for prostate cancer cells at low testosterone concentrations

The prostate specific antigen (PSA) promoter/enhancer has been clearly demonstrated to be tissue specific, and has been applied to prostate-specific gene therapy. However, the transcription of the PSA gene is strictly androgen dependent, and its promoter activity is very weak at low concentrations of testosterone, which are generally observed in prostatic cancer patients treated with androgen deprivation. In this study, we used a partial androgen receptor (ARf) containing amino acids 232-429 and 481-657 to transactivate the PSA gene without androgens. We made two expression vectors, ARfPPLUC and ARfPPTK. They contained ARf cDNA driven by cytomegalovirus promoter and cDNAs of either firefly luciferase (LUC) or herpes simplex virus thymidine kinase (TK) driven by PSA promoter/enhancer (PP). The expressed ARf enhanced the PP activity by about 110-fold in the PSA-producing prostate cancer cell line, LNCaP, under low testosterone concentrations. Moreover, in a PSA-nonproducing prostate cancer cell line, DU145, ARf also enhanced the PP activity by about 60-fold in an androgen-independent manner. In a growth inhibition assay, ARfPPTK treated with ganciclovir was found to inhibit the cell growth of LNCaP cells much more effectively than PPTK. Furthermore, in contrast to PPTK, ARfPPTK also had an inhibitory effect on DU145 cells. This system is thus considered to provide a useful therapeutic option in patients with prostate cancer who are receiving hormonal therapy.

Inhibition of glucocorticoid-induced apoptosis by the expression of antisense gene of mitochondrial ATPase subunit 6(1)

To isolate the apoptosis-linked genes involved in the cell death of thymocytes induced by glucocorticoids, we developed a functional cloning assay. Murine CD4(+)CD8(+) thymic cell line 2-257-20 cells were transfected with cDNA expression libraries obtained from a dexamethasone-resistant cell line. The transfected cells were selected in the presence of dexamethasone, and the plasmids which episomally expanded were then extracted from the surviving cells. One of the rescued cDNAs was found to be an antisense cDNA fragment identical to the mouse mitochondrial ATPase 6 gene. In the stable transfectants with the ATPase 6 antisense gene, the induction of apoptosis by dexamethasone was significantly delayed. Furthermore, the ATP synthesis in these transfectants was also reduced to some extent. ATPase 6 is a subunit of F(o)F(1) ATPase and our results support that ATP synthesis from the mitochondria is necessary for the induction of apoptosis induced by glucocorticoids.

Expression of carbonic anhydrase I or II and correlation to clinical aspects of colorectal cancer

BACKGROUND/AIMS

This study was undertaken to elucidate the correlation between the expression of carbonic anhydrase I or II and the characteristic features of colorectal cancer.

METHODOLOGY

The carbonic anhydrase I or II expressions of 74 colorectal cancer patients were analyzed by Western blotting. The relative intensity of cancer to the paired normal mucosa was calculated, and then compared with the clinicopathological parameters. Furthermore, a multivariate analysis for synchronous distant metastasis was undertaken.

RESULTS

The expression of carbonic anhydrase I in colon cancer or carbonic anhydrase II in rectal cancer with Duke's D was found to be significantly lower than that with Duke's B or C, respectively. Similarly, carbonic anhydrase I in colon cancer or carbonic anhydrase II in rectal cancer with moderate-severe budding was found to be significantly lower than that with none-mild budding, respectively. Based on the findings of a logistic regression analysis, carbonic anhydrase I was adopted for colon cancer (P = 0.057) and carbonic anhydrase II for rectal cancer (P = 0.008) regarding synchronous distant metastasis.

CONCLUSIONS

The expressions of carbonic anhydrase I and II correlated with biological aggressiveness of colorectal cancer and synchronous distant metastasis, especially carbonic anhydrase I for colon cancer and carbonic anhydrase II for rectal cancer.

Mouse CD8+ CD122+ T cells with intermediate TCR increasing with age provide a source of early IFN-gamma production

Although CD8+ IL-2Rbeta (CD122)+ T cells with intermediate TCR reportedly develop extrathymically, their functions still remain largely unknown. In the present study, we characterized the function of CD8+ CD122+ T cells with intermediate TCR of C57BL/6 mice. The proportion of CD8+ CD122+ T cells in splenocytes gradually increased with age, whereas CD8+ IL-2Rbeta-negative or -low (CD122-) T cells conversely decreased. The IFN-gamma production from splenocytes stimulated with immobilized anti-CD3 Ab in vitro increased with age, whereas the IL-4 production decreased. When sorted CD8+ CD122+ T cells were stimulated in vitro by the anti-CD3 Ab, they promptly produced a much larger amount of IFN-gamma than did CD8+ CD122- T cells or CD4+ T cells, whereas only CD4+ T cells produced IL-4. The depletion of CD8+ CD122+ T cells from whole splenocytes greatly decreased the CD3-stimulated IFN-gamma production and increased the IL-4 production, whereas the addition of sorted CD8+ CD122+ T cells to CD8+ CD122+ T cell-depleted splenocytes restored the IFN-gamma production and partially decreased IL-4 production. It is of interest that CD8+ CD122+ T cells stimulated CD4+ T cells to produce IFN-gamma. The CD3-stimulated IFN-gamma production from each T cell subset was augmented by macrophages. Furthermore, CD3-stimulated CD8+ CD122+ T cells produced an even greater amount of IFN-gamma than did liver NK1.1+ T cells and also showed antitumor cytotoxicity. These results show that CD8+ CD122+ T cells may thus be an important source of early IFN-gamma production and are suggested to be involved in the immunological changes with aging.

The potential role for nephritis-associated plasmin receptor in acute poststreptococcal glomerulonephritis

Immunoglobulin G from a patient convalescing from acute poststreptococcal glomerulonephritis (APSGN) bound specific antigenic sites in early APSGN glomeruli. A streptococcal cytoplasmic antigen (preabsorbing antigen, PA-Ag), could selectively preabsorb fluorescein isothiocyanate (FITC)-labeled IgG and prevented glomerular staining. The antigen was purified and identified as an M(r) approximately 43,000 protein with a pI of 4.7 that strongly activated complement C3 (N. Yoshizawa, S. Oshima, I. Sagel, J. Shimizu, and G. Treser, 1992, J. Immunol. 148, 3110-3116). In the present study, a nephritogenic antigen was purified by affinity chromatography using APSGN IgG-immobilized Sepharose followed by chromatography on an anion-exchange resin. Purification was monitored by ELISA and Western blotting using the binding characteristics of the specific antibodies present in APSGN serum. The molecular weight of the purified antigen, named nephritis-associated plasmin receptor (NAPlr), was an M(r) approximately 43,000 protein and the internal amino acid sequence was found to be homologous to those of the plasmin receptor (Plr) of group A streptococci strain 64/14 and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from Bacillus subtilis. The purified NAPlr exhibited GAPDH activity and plasmin(ogen) binding activity. Using FITC-labeled rabbit anti-NAPlr, the antigen was found to be present in the glomeruli of 22 of 22 patients in the early stage of APSGN. Bacterial Plr was also demonstrated in human APSGN glomeruli for the first time using monoclonal antibody to the recombinant Plr protein. Antibody to NAPlr was found in the sera of 46 of 50 (92%) patients within 3 months of onset. These results led us to speculate that NAPlr bound to the glomeruli may contribute to the pathogenesis of APSGN via plasmin and complement activation.

Selective inhibition of hepatoma cells using diphtheria toxin A under the control of the promoter/enhancer region of the human alpha-fetoprotein gene

We constructed a plasmid containing human alpha-fetoprotein (AFP) promoter/enhancer to direct the cell type-specific expression of diphtheria toxin fragment A (DTA), designated as pAF-DTA, to AFP-producing hepatocellular carcinoma cells. The transfection was carried out with cationic liposomes (DMRIE-C) and the expression of the DTA gene was confirmed by a northern blot analysis. When pAF-DTA was transfected, the growth of AFP-positive HuH-7 cells was inhibited, whereas growth inhibition was not observed in AFP-negative MKN45 cells. In this experiment, the secretion of AFP was similarly suppressed, but the secretion of carcinoembryonic antigen from MKN45 was not altered. pAF-DTA could also exert its growth inhibitory effect on PLC, a cell line with a low level of AFP. However, no inhibitory effect of pAF-DTA was observed on the proliferation of primary hepatocyte cells. Furthermore, transfection experiments in which HuH-7 and splenic stromal cells were co-cultured revealed the growth inhibition by pAF-DTA to be selective in HuH-7 cells. Finally, the growth of HuH-7 transplanted on BALB/c nu/nu mice was inhibited by the direct injection of pAF-DTA/liposome complex into a tumor mass. These results suggest that use of pAF-DTA may be potentially useful as a novel approach for the selective treatment of tumor cells producing AFP even at low levels, without affecting other types of cells.

Cell-specific expression of the diphtheria toxin A-chain coding sequence under the control of the upstream region of the human alpha-fetoprotein gene

BACKGROUND AND OBJECTIVES

Development of the system to express a suicide gene selectively in tumor cells is essential for gene therapy. We constructed a plasmid containing the diphtheria toxin A (DTA) fragment linked to human alpha-fetoprotein (AFP) promoter and enhancer, and tested whether it can exert its cytocidal effect selectively on AFP-producing cells.

METHODS

The chloramphenical acetyltransferase (CAT) reporter gene or DTA gene was linked to the 5' upstream region of the AFP gene. The plasmids were transfected into AFP-producing or non-producing cells by the lipopolyamine-coated DNA method. Expression of CAT activity and effects on cell growth of transfected cells were assessed.

RESULTS

When the AFP-producing cells HuH-7 or HepG2 were cotransfected with CAT reporter plasmid and pAF5.1DTA plasmid, the CAT activity was greatly suppressed. In contrast, cotransfection with pAF5.1DTA-R, the inversely inserted DTA gene, did not inhibit CAT activity. Furthermore, cell growth of HuH-7 cells transfected with pAF5.1DTA plasmid was significantly inhibited compared with HuH-7 cells transfected with DTA-R plasmid.

CONCLUSIONS

Our results indicate that selective killing of AFP-producing cells will be attained by introducing the DTA gene linked to the promoter and enhancer region of AFP.

Cell-specific expression of the diphtheria toxin A-chain coding sequence under the control of the upstream region of the human alpha-fetoprotein gene

BACKGROUND AND OBJECTIVES

Development of the system to express a suicide gene selectively in tumor cells is essential for gene therapy. We constructed a plasmid containing the diphtheria toxin A (DTA) fragment linked to human alpha-fetoprotein (AFP) promoter and enhancer, and tested whether it can exert its cytocidal effect selectively on AFP-producing cells.

METHODS

The chloramphenical acetyltransferase (CAT) reporter gene or DTA gene was linked to the 5' upstream region of the AFP gene. The plasmids were transfected into AFP-producing or non-producing cells by the lipopolyamine-coated DNA method. Expression of CAT activity and effects on cell growth of transfected cells were assessed.

RESULTS

When the AFP-producing cells HuH-7 or HepG2 were cotransfected with CAT reporter plasmid and pAF5.1DTA plasmid, the CAT activity was greatly suppressed. In contrast, cotransfection with pAF5.1DTA-R, the inversely inserted DTA gene, did not inhibit CAT activity. Furthermore, cell growth of HuH-7 cells transfected with pAF5.1DTA plasmid was significantly inhibited compared with HuH-7 cells transfected with DTA-R plasmid.

CONCLUSIONS

Our results indicate that selective killing of AFP-producing cells will be attained by introducing the DTA gene linked to the promoter and enhancer region of AFP.

Inhibitory effect of protease inhibitor on endothelial cell activation

BACKGROUND

Endothelial cells (EC) are important for regulating the hemostatic balance of prothrombotic and antithrombotic activities. Proinflammatory cytokines such as tumor necrosis factor-alpha (TNFalpha) play an important role in the regulation of EC and also regulate the production of plasminogen activator inhibitor type 1 (PAI-1), which is an EC-producing factor with the inhibitory activity of fibrinolysis, and the expression of intercellular adhesion molecule-1 (ICAM-1), which is an adhesion molecule that plays an important role in inflammation. Protease inhibitors such as gabexate mesilate (GM) and ulinastatin (UTI) have been shown to improve the microcirculatory environment and reduce tissue damage, but the mechanism for this has yet to be fully elucidated. We investigated the effect of GM or UTI on EC regarding PAI-1 synthesis and ICAM-1 expression.

METHODS

Human umbilical vein endothelial cells (HUVECs) were obtained and stimulated with TNFalpha. GM or UTI was added to HUVECs just before TNFalpha stimulation. The PAI-1 activity in the culture medium of HUVECs was measured by using an enzymatic assay kit. The PAI-1 mRNA expression was assayed by a semiquantitative reverse transcriptase polymerase chain reaction assay. The ICAM-1 expression on HUVECs was assayed by a flow cytometric analysis.

RESULTS

GM inhibited the PAI-1 synthesis of HUVECs stimulated with TNFalpha in a dose-dependent manner as shown by the mRNA expression. However, UTI was not able to inhibit PAI-1 synthesis. In contrast, both GM and UTI significantly inhibited the ICAM-1 expression on HUVECs stimulated with TNFalpha.

CONCLUSIONS

These data suggest that GM may thus provide a beneficial effect which improves the microcirculatory environment and prevents tissue damage by inhibiting the activation of the vascular EC themselves.

Carbonic anhydrase I and II as a differentiation marker of human and rat colonic enterocytes

Carbonic anhydrase (CA) is an enzyme that is expressed in the intestine and catalyzes the reversible hydration of CO2 in the following reaction: CO2 + H2O<==>H2CO3<==>H(+)+HCO3-. To elucidate the association of CA expression with the differentiation of colonic enterocytes, we investigated the expression and localization of CA using a Northern blotting analysis, Western blotting analysis, and immunohistochemical staining. A Northern blotting analysis revealed an abundant expression of CA I and II mRNA in the colonic epithelial cells. However, the expression of CA III mRNA was not detected. According to the results of immunohistochemical staining of the human colonic mucosa using antisera against CA I and II, both CA I and II were localized on the cytoplasm of non-goblet columnar cells in the upper half of the crypts where more differentiated cells are located. According to the results of immunohistochemical staining of the rat colonic mucosa, neither CA I and II were detected at the new-born stage. The expression of CAs in the upper half of the crypts began to rise from 1 week after birth, and thereafter increased according to the growth of the rats. At 3 weeks after birth, the expression of CAs was almost the same as that of the adult rats. The amount of CA proteins evaluated by a Western blotting analysis revealed that the expression of CAs increased gradually until reaching a maximum level at 6 or 8 weeks. These results therefore suggest that CA I and II appear to be good markers for the differentiation of enterocytes in the colonic mucosa.

Enhancement of activation-induced cell death by fibronectin in murine CD4+ CD8+ thymocytes

Development of T cells in the thymus is achieved through the interactions of thymocytes with their microenvironments. This study focused on the function of fibronectin (FN), a major extracellular matrix molecule in the thymus, in the cell death induced by activation via the T-cell antigen receptor. FN alone did not increase cell death in murine thymocytes above the baseline level, but it significantly enhanced the cell death induced by fixed anti-CD3 monoclonal antibody (mAb), especially when a high concentration of anti-CD3 mAb was used. DNA fragmentation increased in parallel with cell death, indicating that cell death was a result of the apoptosis. Fluorescence-activated cell sorter (FACS) analysis revealed that the activation-induced cell death (AICD) caused by anti-CD3 mAb alone, or by a combination of anti-CD3 mAb and FN, occurred selectively in CD4+ CD8+ thymocytes. Very late activation antigen (VLA)-4 and VLA-5 are two major ligands to FN on thymocytes. The expression of both ligands was investigated at different stages of thymocyte development. VLA-4 was predominantly expressed at the CD4- CD8- stage, and thereafter the expression was reduced, whereas VLA-5 was constantly expressed during maturation. Furthermore, the enhancing effect by FN was inhibited in the presence of the Gly-Arg-Gly-Asp-Ser-Pro (GRGDSP) peptide but not in the presence of the connecting segment-1 (CS-1) peptide, suggesting that enhancement of AICD observed in CD4+ CD8+ thymocytes is mediated through VLA-5.

Cloning and expression of an alpha-2,8-polysialyltransferase (STX) from Xenopus laevis

Polysialic acid (polySia) is a carbohydrate structure found on neural cell adhesion molecules (N-CAM). Two polysialyltransferases (polySiaTs) that catalyze synthesis of polySia have been described, and designated PST-1/PST/ST8SiaIV and STX/ST8SiaII. We cloned a polySiaT (xSTX) from a nonmammalian vertebrate, Xenopus laevis . xSTX had 80% amino acid similarity to the rat STX. This clone induced polySia expression when transfected into polySia-negative COS-1 cells. Northern blot analysis of whole embryos at different stages of development revealed that xSTX mRNA was most abundantly expressed in premetamorphic stages. The relative level of xSTX and N-CAM mRNAs was also examined and found to change in parallel to the extent of polysialylation on N-CAM. In adult tissues, the expression of xSTX mRNA was restricted to brain, eye and heart, which also expressed polySia. These results suggest that xSTX is the major enzyme responsible for the synthesis of polysialylated N-CAM in embryos at certain stages of development and also in adult tissues.

Molecular cloning of ssd-form neural cell adhesion molecules (N-CAMs) as the major form in Xenopus heart

Different forms of neural cell adhesion molecule (N-CAM) are generated by alternative splicing of primary transcripts and considered to have distinct biological functions. We cloned cDNAs encoding a new form of N-CAMs from the Xenopus heart cDNA library. Comparison of the sequences with chicken and mouse N-CAMs revealed that these clones code for ssd-form N-CAM. We demonstrate by Northern blot analysis that the ssd form is the major form expressed in the Xenopus adult heart. We obtained two types of ssd-form N-CAM, which are transcripts from N-CAM 1 and N-CAM 2 genes. Both types contain muscle specific domain (MSD) but not pi domain. Northern blot analysis also indicated that this form is not expressed in adult brain, in which ld-form N-CAM is the main N-CAM expressed. It is possible that high levels of specific expression of ssd-form N-CAM are related with the differentiation of cardiac muscles.

[Molecular mechanism of apoptosis operated in the immune system]

Apoptosis is the physiological cell death, and plays an important role in the various fields of immunology, especially (1) in the formation of T cell and B cell repertoires, (2) in the regulation of hyper-activated T and B cells by Fas-FasL, and (3) in the effector phases of eliminating potentially dangerous cells. Although, the exact mechanism of cell death is still unknown, progress has been made in identifying key elements in apoptosis. Particularly, ICE family was found essential for apoptotic execution, and Bcl-2 related proteins can block the molecular events of apoptosis. This article briefly reviewed such "on" and "off" signals in apoptosis, and discussed from the view point that the disturbance of the balance of these signals are relevant to the etiology of autoimmune diseases.

Improvement of pharmacokinetics and antitumor activity against human hepatoma cell line by using adriamycin-entrapped stealth liposomes

Preferential accumulation in the reticuloendothelial system is one of the major obstacles to the use of liposomes as a drug carrier for targeting therapy. To reduce their uptake, ganglioside GM1 was introduced into the components of conventional liposomes that had been used in our targeting experiments. Two types of such liposomes were prepared. Tissue distribution studies on Adriamycin entrapped in both types of liposomes clearly indicated that the uptake of Adriamycin by liver and spleen decreased to the level comparable to that of free Adriamycin administration. By contrast, the level of Adriamycin in the serum remains high, and some increase was observed in the accumulation to the tumor. Furthermore, Adriamycin in these liposomes, which were conjugated with anti-alpha-fetoprotein (AFP) antibody, inhibited the growth of AFP-positive human hepatoma Li-7 more efficiently than free Adriamycin or Adriamycin in antibody-conjugated conventional liposomes.

Antibody specific for phosphorylated AMPA-type glutamate receptors at GluR2 Ser-696

Possible phosphorylation sites on the Purkinje cell alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-type glutamate receptor subunits were identified using in vitro kinase assays of 17 synthetic peptides derived from the transmembrane-3 (TM3) domain to the end of C-terminal of a rat glutamate receptor 2 (GluR2). Only two peptides containing Ser-662 and Ser-696 were found to be efficiently phosphorylated by protein kinase C (PKC). The peptide including Ser-696 was also phosphorylated by protein kinase G (PKG). Another peptide containing Thr-692 of a rat GluRA, clone almost identical to GluR1, was phosphorylated by PKC but not by PKG. Antisera recognizing phosphorylated AMPA receptor subunits at GluR2 Ser-696 or the homologous sites of GluR1/3/4 were produced, and the specificity of one of them, named 12P3, was established by enzyme-linked immunosorbent assay (ELISA), immunoblot and immunoprecipitation analyses. 12P3-immunocytochemistry on cerebellar slices demonstrated an AMPA-induced transient AMPA receptor phosphorylation, which appeared in Purkinje cell dendrites as well as somata immediately after AMPA treatment and disappeared after 20 min. This antibody may be a useful tool to study the role of AMPA receptor phosphorylation in producing synaptic plasticity.

Purification and characterization of acid cysteine protease from metacercariae of the mammalian trematode parasite Paragonimus westermani

Acid cysteine protease was purified from metacercariae of the mammalian trematode parasite Paragonimus westermani. The purified enzyme had a molecular mass of 27 kDa and was a monomeric polypeptide. The protease had an absolute requirement for a reducing agent for full activity towards fluorescein-isothiocyanate-labeled hemoglobin, and it was active in the acidic pH range, with an optimum pH of 4.0. While acidic proteolysis was insensitive to the aspartic protease inhibitor pepstatin A, activity was significantly inhibited by the cysteine protease inhibitors, leupeptin, chymostatin and L-trans-epoxy-succinyl-L-leucylamido(4-guanidino)-butane. The sensitivity of the enzyme to the inhibitors was similar to that of cathepsins B and L, but the specificity of the protease towards chromogenic substrates was slightly different from that of the cathepsins. The purified enzyme was highly specific for N-substituted peptidyl substrates containing arginine in the P1 position and phenylalanine in the P2 position, and the protease extensively degraded human native proteins, such as human serum albumin, immunoglobulins, complement components and also endogenous protease inhibitors. Since the protease hydrolyzes both soluble proteins and components of human defense systems, it may facilitate parasite nutrition and evasion of host defense mechanisms.

Single-cell observation of calcium signals in T cells and antigen-presenting cells during antigen presentation

Intracellular calcium ion mobilization in T-cell hybridomas and antigen-presenting cells (APC) during the interaction was observed using confocal fluorescence microscopy. No calcium signal was detected in non-activated T-cell hybridomas by antigen presentation. However, in activated T-cell hybridomas, intracellular calcium ion concentration rapidly increased by antigen presentation and thereafter apoptosis was induced. On the contrary, during the interaction with T-cell hybridomas, calcium signal was induced in APCs irrespective of the activation of T-cell hybridomas. Chemical modification of APCs with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide, which is known to induce T-cell unresponsiveness during antigen presentation, inhibited cap formation of surface MHC class II molecules and suppressed calcium signals during the interaction with T-cell hybridomas.

In vivo function of homing receptors participating in lymphocyte recirculation: transfer analysis in SCID mice

In order to examine the in vivo function of the adhesion molecules implicated in lymphocyte homing, blocking effects of antibodies against various adhesion molecules on lymphocyte migration were tested in SCID mice into which BALB/c donor splenocytes had been transferred. It was proved that the transferred donor splenocytes migrated to peripheral lymph nodes (LNs) of SCID mice. T and B lymphocytes were distributed in the specialized compartments as seen in the LNs of normal mice. Migration of lymphocytes to the local LNs was accelerated by stimulation with ovalbumin and complete Freund's adjuvant. This experimental system with accelerated migration was applied to analyze the in vivo function of adhesion molecules, and the following findings were obtained. Combined use of antibodies against lymphocyte-function-associated antigen 1 (LFA-1) and intercellular adhesion molecule 1 (ICAM-1) strongly inhibited the migration of T lymphocytes to the peripheral LNs. Antibodies against very late antigen 4 (VLA-4) and vascular cell adhesion molecule 1 (VCAM-1) led to diminished B lymphocyte migration and disturbed compartmentalization of T lymphocytes in the paracortex. Migration of both T and B lymphocytes to the LNs was completely inhibited by the antibody against L-selectin. These results indicate that L-selectin plays an essential role in migration of both T and B lymphocytes into peripheral LNs but LFA-1/ ICAM-1 and VLA-4/VCAM-1 play different roles in compartmentalization of T and B lymphocytes in the peripheral LNs. In contrast, these adhesion molecules were not involved in lymphocyte migration to the splenic white pulp, indicating that the mechanisms for lymphocyte homing to the white pulp are quite different from those to the peripheral LNs.

Naive T cells can mediate delayed-type hypersensitivity response in T cell receptor transgenic mice

We produced transgenic mice expressing T cell receptor-alpha beta chain genes, derived from the chicken ovalbumin (OVA)-specific I-Ad-restricted CD4+CD8- T helper cell clone 7-3-7. In transgenic mice with H-2d genetic background (Tg-d mice), delayed-type hypersensitivity (DTH) was induced in the hind footpad by one inoculation with OVA without any previous sensitization, suggesting that naive T cells have the potential to be involved in DTH response. Spleen cells from nonimmunized Tg-d mice showed a strong T cell proliferative response to in vitro stimulation with OVA. Furthermore, these spleen cells produce cytokines including interleukin(IL)-2, IL-3, interferon-gamma, granulocyte/macrophage colony-stimulating factor, macrophage inflammatory protein (MIP)-1 alpha and MIP-1 beta, which may play an important role in the attraction of mononuclear cells to an antigen-challenging site.

Acceleration of diabetes in young NOD mice with peritoneal macrophages

To elucidate the roles of macrophages in the pathogenesis of NOD murine diabetes, peritoneal macrophages from NOD mice were injected into young NOD mice. We used 12 to 20 week-old NOD mice of both sexes as donors, and sex-matched 2-week-old NOD mice as recipients. Cyclophosphamide (CY), 200 mg/kg, was intraperitoneally injected into the donors. Two weeks later, peritoneal exudate cells (PEC) were collected from the diabetic donors. Macrophage-rich fractions (MRF) were collected by adherence. Then PEC(5-8 x 10(6)) or MRF(3-7 x 10(6)) were transferred, intraperitoneally, to the recipients. Two weeks later, some of the recipients were killed in order to perform immunofluorescent analysis of splenocytes and to assess pancreatic histology. Mac 1 positive splenocytes were increased in PEC- and in MRF-injected recipient mice. Insulitis was seen in PEC- and MRF-injected mice, but not in controls. Some of the recipients were injected with CY, 200 mg/kg, intraperitoneally, at two weeks post cell transfer. Two weeks after CY injection, the animals were examined for the presence of diabetes. The incidences of diabetes were 67% in PEC-injected mice, 40% in the MRF-injected group, and 3% in the controls. These results suggest that peritoneal macrophages accelerate the disease process in NOD mice.

Improvement of therapeutic effect by using Fab' fragment in the treatment of carcinoembryonic antigen-positive human solid tumors with adriamycin-entrapped immunoliposomes

To improve the therapeutic efficiency adriamycin entrapped in antibody-conjugated liposomes, Fab' fragment was used instead of the whole antibody molecule. The murine monoclonal antibody, 21B2, against human carcinoembryonic antigen (CEA) was digested with pepsin, and the thiol residue of intra-heavy chain produced by reduction of F(ab')2 with dithiothreitol was conjugated to liposomes containing adriamycin. The tissue distribution of adriamycin delivered with these liposomes was studied in BALB/c nu/nu female mice bearing CEA-positive human gastric cancer strain MKN-45. An increase in delivery of adriamycin to the tumor was observed in the mice given liposomes with Fab' fragment as compared to those given liposomes with whole antibody. However, the preferential distribution of adriamycin in liposomes to the reticuloendothelial cells remained the same regardless of the use of Fab' fragment. For investigation of in vivo therapeutic effect, three i.v. injections of free adriamycin or adriamycin in liposomes equivalent to 5 mg/kg were given, and adriamycin in Fab' fragment-conjugated liposomes was found most effective in the inhibition of tumor growth. This was confirmed in terms of actual tumor weights excised and CEA concentration in the blood, as well as by pathological observations. The advantages of using Fab' fragment instead of whole antibody are discussed.

[Apoptosis in immunology]

Apoptosis is the physiological cell death, and recent studies have revealed that apoptosis plays an important role in the various fields of immunology. Especially, in the formation of T or B cell repertoires, the cells reactive to self antigens are eliminated by the induction of apoptosis, whereas the cells competent to react against foreign antigens are saved for survival by the suppression of apoptosis. Furthermore, apoptosis is employed as the destruction mechanism of target cells in killer T cells or NK cells. The disturbance of apoptosis-mechanism, therefore, will be strongly relevant for the etiology of autoimmune diseases and carcinogenesis.

[The role of apoptosis in the development of T cells]

T cells are responsible for the discrimination of self and nonself. To acquire such activities, however, T cells must encounter two selections in the thymus, namely positive and negative selections. Recent data from in vivo and in vitro experiments strongly indicated that apoptosis is involved in these selections, especially in the elimination of the cells reactive to self antigens. This article briefly reviewed the roles of apoptosis in the development of T cells in the thymus.

Preferential induction of IL-4 is determined by the type and duration of antigenic stimulation

The transition of lymphokine production from IL-2 to IL-4 was investigated with antigen-primed lymph node cells (LNC) by observing cytokine release following sequential cycles of antigen exposure in vitro. LNC from mice infected with Nippostrongylus brasiliensis (Nb), Trichinella spiralis, or primed with giant ragweed pollen demonstrated a pattern of dominant IL-2 production at 24 hr; however, there was a switch to predominantly IL-4 production within 72 hr following the first cycle of in vitro antigenic stimulation. In addition, repeated antigenic stimulation with these antigens shifted the pattern to IL-4 production. In contrast, only IL-2 production was observed after a single cycle of in vitro antigenic challenge with haptens (e.g., NP-O-succinimide or trimethylammonium hapten) or the naive allogenic spleen cells. Thereafter, the lymphokine production pattern gradually changed from IL-2 alone to mixtures of IL-2 and IL-4, and finally to predominant IL-4 secretion. In contrast, following priming with purified protein derivatives (PPD), it was difficult to detect IL-4 release even after nine successive weekly stimulations. However, activation of PPD-primed cells with anti-CD3 antibody resulted in IL-4 secretion. Furthermore, Nb-primed T cells, which produced IL-4 alone after repeated antigenic stimulation, produced IL-2 when stimulated in the presence of cycloheximide. These results suggest that (1) immune populations regulate cytokine production, (2) the IL-2/IL-4 profile is dependent on the type and duration of antigenic stimulation, and (3) production or accumulation of cycloheximide-sensitive proteins is critical for the switch from IL-2 to IL-4 secretion.

Possible application of the laser in immunobiology

The human immune system acts a defence mechanism against exogenous or indigenous potentially harmful bodies, such as bacteria and viruses. The major histocompatibility complex (MHC class I and class II antigens) form key elements of legitimate body components, and the organization of MHC molecules allows T-lymphocytes to distinguish between legitimate and foreign bodies. On detection of a foreign component, T-cells activate the necessary pathways for destruction of the foreign body. Occasionally however the system breaks down and the result is a disease of an autoimmune nature. Both visible light and infrared low reactive-level laser therapy (LLLT) has been shown to act on immune system cells in a number of ways, activating the irradiated cells to a higher level of activity. Infrared LLLT has been shown to increase both the phagocytic and chemotactic activity of human leukocytes in vitro, for example. This is an example of photobiological activation. Photobiological cell-specific destruction is also possible using doses of low incident laser energy on cells which have been photosensitized for the specific wavelength of the laser, such as in photodynamic therapy (PDT) for superficial cancers. LLLT has also been shown to act directly and selectively on the autoimmune system, restoring immunocompetence to immunocompetence cells. Although much more research needs to be done, there are enough experimental and clinical data to show that the laser, and LLLT in particular, has a possibly exciting role both in immunobiological therapy for diseases of the immune system, and to activate and boost the normal reaction of the immune system components against harmful foreign bodies.

Tumour necrosis factor-alpha enhances cAMP-induced programmed cell death in mouse thymocytes

During T-lymphocyte differentiation in the thymus, the majority of thymocytes die by apoptosis in situ. This process is characterized by internucleosomal DNA fragmentation and is induced by a number of stimuli including glucocorticoids, calcium ionophore, cAMP and 12-o-tetradecanoylphorbol 13-acetate (TPA). In this study, the effect of cytokines tumour necrosis factor-alpha (TNF-alpha) and interferon gamma (IFN-gamma) on the programmed cell death of thymocytes was examined by measuring DNA fragmentation and LDH release. TNF-alpha and IFN-gamma had no effect on DNA fragmentation in control and TPA, or A23187-treated thymocytes. Both human and murine rTNF-alpha enhanced cAMP-induced programmed cell death dose-dependently, but IFN-gamma had no effect on the process. TNF-alpha did not stimulate cAMP accumulation in control or 2-chloroadenosine-treated thymocytes. TPA markedly stimulated cAMP-induced DNA fragmentation as a result of 6 h incubation, whereas TNF-alpha did not. Thus TNF-alpha did not appear to activate protein kinase C directly. The effect of TNF-alpha was observed in the cell preparations from which adherent cells had been removed, suggesting that cytokines secreted by adherent cells in response to TNF-alpha are not involved in the process. The enhancement of cAMP-induced DNA fragmentation was observed in CD4+CD(8+)-double positive cells, but not in CD4+CD(8-)-single positive cells. The results of the present study indicate that a physiological cytokine, TNF-alpha, may modulate programmed cell death in immature thymocytes in concert with cAMP.

Topoisomerase inhibitors induce apoptosis in thymocytes

The effects of the inhibitors of topoisomerase I and II, camptothecin and etoposide, as well as novobiocin and adriamycin, on the DNA fragmentation and viability of mouse thymocytes in primary culture were examined. All inhibitors were shown to produce dose-dependent internucleosomal DNA cleavage by resolving isolated DNA by agarose-gel electrophoresis. The DNA fragmentation seemed to precede cell death, determined on the basis of LDH release, by a few hours. Etoposide-induced DNA fragmentation progressively increased after incubation and was enhanced by pretreatment with phorbol 12,13-dibutyrate, a phorbol ester capable of activating protein kinase C, whereas camptothecin-induced DNA fragmentation increased progressively after 12 h incubation and was unaffected by phorbol 12,13-dibutyrate-pretreatment. The process was also energy-dependent and required RNA and protein synthesis and protein phosphorylation, since it was inhibited by sodium azide, actinomycin D, cycloheximide and 1-(5-isoquinoline-sulfonyl)-2-methylpiperazine hydrochloride, a protein kinase inhibitor. DNA fragmentation was also inhibited by zinc ions, suggesting the involvement of a specific endonuclease in DNA cleavage. These phenomena are similar to those detected in thymocytes undergoing apoptosis following exposure to glucocorticoids (Cohen, J.J. and Duke, R.C. (1984) J. Immunol. 132, 38-42). Considering that topoisomerases function in cellular proliferation and differentiation by altering DNA topology, the results suggest that topoisomerases have important roles in T-lymphocyte ontogeny in the thymus and are in part involved in the elimination of autoreactive or harmful cells by an apoptotic process.

Effect of liposomal interleukin-2 on ascites-forming rat hepatoma

Interleukin-2 was entrapped in liposomes (Lip-IL-2) and injected into rats. The intraperitoneal injection of Lip-IL-2 into rats bearing an ascites-forming rat hepatoma (AH-66) significantly increased the survival time when compared with rats administered free IL-2 or saline-containing liposomes. The number of peritoneal exudate cells (PEC) increased markedly after intraperitoneal injection of Lip-IL-2 and consisted mainly of macrophages. The level of tumor necrosis factor alpha (TNF-alpha) and the intensity of free radicals increased in the ascites at 48 hrs after Lip-IL-2 administration, whereas TNF-alpha was not detected and the intensity of free radicals did not increase after free IL-2 administration. Our findings suggested that entrapment of IL-2 into liposomes enhanced its potential for cancer therapy, presumably by activating macrophages to produce TNF-alpha and free radicals.

Inhibition of programmed cell death by cyclosporin A; preferential blocking of cell death induced by signals via TCR/CD3 complex and its mode of action

Cyclosporin A (CsA) is reported to inhibit programmed cell death. We confirmed this by using T-cell hybridomas which are inducible to programmed cell death by activation with immobilized anti-CD3 antibody or with anti-Thy 1.2 antibody. Cell death and DNA fragmentation, characteristic features of programmed cell death, were almost completely blocked by CsA or FK506. To investigate whether CsA inhibits only the cell death through the signals via the TCR/CD3 complex or all of the programmed cell death induced by various reagents, we further established CD4+8+ thymic lymphomas which result in programmed cell death after activation with calcium ionophore, dexamethasone, cyclic AMP or anti-CD3 antibody. It was revealed that CsA could block only the cell death mediated by the TCR/CD3 complex. For the clarification of the site of action of CsA, Ca2+ influx and endocytosis of receptors after stimulation with anti-CD3 antibody were monitored in the presence of CsA, and no significant effects of CsA were observed. Furthermore, prevention of cell death was examined by adding CsA at various periods of time after initiation of culture. CsA was found to exert its effect even when added after 4 h of cultivation, and the kinetic pattern of suppression was similar to that of the suppressive effect on IL-2 production. These observations indicate that in the events of programmed cell death, the major site of action of CsA will not be the inhibition of the immediate membrane events after activation of the TCR/CD3 complex but rather the interference in the function of molecules that transmit signals between membrane events and the activation of genes in the nucleus.

HLA class II antigens are associated with Japanese pemphigus patients

We investigated the HLA class II antigens in 30 Japanese cases of pemphigus, 17 cases of pemphigus vulgaris (PV) and 13 cases of pemphigus foliaceus (PF), by both serologic and restriction fragment length polymorphism (RFLP) analyses. We detected two major haplotypes susceptible to PV, i.e., DRw12-DQw7 and DRw6-DQw5. In contrast, DR2 was absent in PV. RFLP analyses showed that DRw6 PV patients had a disease-associated restriction fragment representing DQw5, the same association as that found in DRw6 Jewish PV patients. However, DRw12 Japanese PV patients had DQw7, whereas DR4 Jewish PV patients had DQw8. On the other hand, all 13 PF patients were serologically typed for DQw1, which could not be further subdivided into DQw5 by RFLP analyses. These results suggest that Japanese and Jewish PV patients may be immunogenetically closely related to each other, but Japanese PV patients appear to be immunogenetically different from Japanese PF patients.

Inhibition of growth of rat hepatoma by local injection of liposomes containing recombinant interleukin-2. Antitumor effect of IL-2 liposome

Human recombinant interleukin-2 (IL-2) was entrapped in liposome, consisting of egg phosphatidylcholine (PC) and cholesterol. The peri-tumor injections of IL-2 liposome inhibited significantly the growth of solid tumor and prolonged the survival time of rats with solid tumors which were induced by a subcutaneous (s.c.) inoculation of AH-66 cells. Immunohistochemical staining of peritoneal exudate cells and tumor tissues revealed a marked accumulation of activated macrophages in and around the tumor tissues induced by the local injections of IL-2 liposome.

Modulation of thymocyte apoptosis by isoproterenol and prostaglandin E2

Isoproterenol and prostaglandin E2 increased cAMP levels in mouse thymocytes transiently, but failed to induce significant internucleosomal DNA fragmentation in thymocytes with a 24-hr incubation. However, these substances showed synergistic interaction with forskolin in the accumulation of cAMP and DNA fragmentation. The addition of 12-O-tetradecanoyl 13-acetate, an activator of protein kinase C, with isoproterenol or particularly with prostaglandin E2 enhanced DNA fragmentation. These results indicate that an increase in cAMP mediated by isoproterenol or prostaglandin receptor is involved in thymocyte apoptosis through internucleosomal DNA fragmentation in concert with a second signal, the activation of protein kinase C.

12-O-tetradecanoylphorbol 13-acetate potentiates the action of cAMP in inducing DNA cleavage in thymocytes

12-O-Tetradecanoylphorbol 13-acetate (TPA) potentiated the action of cAMP in DNA cleavage in thymocytes induced by a low concentration of adenosine receptor-site agonists such as adenosine, 2-chloroadenosine and forskolin. The enhancement of DNA cleavage by TPA was also observed in dibutyryl cAMP-treated thymocytes. On the other hand, TPA suppressed accumulation of cAMP by the adenosine receptor-site agonists. These results suggest that activation of protein kinase C inhibits cAMP production, but stimulates cAMP-triggered process to induce DNA cleavage and death of thymocytes.

The antitumor effects of adriamycin entrapped in liposomes on lymph node metastases

Adriamycin (ADM) entrapped in liposomes (Lip-ADM) was prepared and its therapeutic effects studied using the mouse leukemia cell line, P388, which metastasized to axillary lymph nodes after inoculation into the foot pads of CDF1 mice. Lip-ADM injections (7.5 mg/kg) were given into the foot pad at two-day intervals. Two series of experiments were performed; one in which Lip-ADM was administered on days 1,3 and 5 following tumor inoculation, and the other in which it was administered on days 5 and 7. Both Lip-ADM injection regimens significantly inhibited metastases to the lymph nodes as compared with mice given injection of saline solution. Furthermore, the therapeutic effects of three Lip-ADM injections were significantly greater than the effects of free ADM. Histological examinations of lymph nodes revealed that three injections of Lip-ADM completely eliminated tumor cells, whereas viable tumor cells were still observed in the lymph nodes after treatment with free ADM. The results of this study suggest that Lip-ADM is useful for the treatment of lymph nodes metastases and that the local injection of Lip-ADM, through such means as endoscopy, would be recommended as a clinical mode of application.

CD4+CD8+ thymocytes are susceptible to DNA fragmentation induced by phorbol ester, calcium ionophore and anti-CD3 antibody

Stimulation of murine thymocytes with phorbol ester or calcium ionophore for 18-24 h resulted in 70%-80% fragmentation of DNA into 180-200-bp multiples, followed by cell death. Experiments with fractionated subpopulations by panning or flow cytometry revealed that DNA fragmentation was selectively observed in CD4+CD8+ cells and in a portion of CD4-CD8+ cells. To investigate whether DNA cleavage is also inducible via antigen-specific receptors, thymocytes were incubated in wells precoated with anti-CD3 antibody. An approximately 20% increase of DNA fragmentation was constantly observed when unseparated thymocytes were stimulated with anti-CD3 antibody. In this anti-CD3-induced DNA degradation, CD4+CD8+ cells are probably the target cells, since (a) fetal thymocytes at day 18 of gestation were found vulnerable to anti-CD3-induced DNA cleavage and (b) flow cytometry analysis of viable cells recovered after cultivation in the anti-CD3-coated wells revealed that CD4+CD8+ cells were preferentially decreased. Further experiments with purified CD4+CD8+ cells, however, could not define a clear-cut increase of DNA fragmentation when isolated CD4+CD8+ cells were stimulated with anti-CD3 antibody. Addition of interleukin (IL) 1, IL 2, IL 3, IL 4 or interferon-gamma to the CD4+CD8+ cell cultures failed to yield a DNA cleavage similar to that of unseparated thymocytes.

Adenosine receptor-mediated accumulation of cyclic AMP-induced T-lymphocyte death through internucleosomal DNA cleavage

Incubation of mouse thymocytes with adenosine and its receptor site agonist, 2-chloroadenosine, induced a pronounced increase in the intracellular cAMP level and resulted in internucleosomal DNA fragmentation followed by cell lysis. Similar DNA fragmentation was induced in peripheral T-lymphocytes prepared from spleen cells but to a lesser extent than in the thymocytes. The DNA fragmentation in both thymocytes and splenic T-lymphocytes was prevented by the addition of actinomycin D and cycloheximide, indicating that this process required mRNA and protein synthesis. The inhibition was accompanied by a reduction in cell lysis as judged by the release of lactate dehydrogenase into the medium. Involvement of cAMP accumulation in inducing DNA fragmentation was supported by the results of experiments with cAMP analogs such as dibutyryl cAMP and 8-bromo-cAMP, and cAMP level-raising drugs including forskolin, cholera toxin, and isobutylmethyxanthine. The latter agents induced pronounced or sustained elevation of cellular cAMP followed by internucleosomal DNA cleavage in T-lymphocytes. These results suggest that adenosine receptor-mediated accumulation of cyclic AMP regulates T-lymphocyte death through inducement of internucleosomal DNA cleavage.

T cell receptor-mediated DNA fragmentation and cell death in T cell hybridomas

Activation of Ag-specific T cell hybridomas with a high density of immobilized anti-CD3 antibody resulted in not only secretion of IL-2 but also cell death of up to 60 to 80% in selected hybridomas after 14 h. Similar results were obtained with V beta 8+ T cell hybridomas stimulated with cross-linked F23.1 antibody. In these activated hybridomas, we found that DNA was fragmented into 180- to 200-bp multiples. DNA fragmentation was not observed when T cells were maintained after killing with anti-Thy-1 plus C or with heat treatment at 45 degrees C, nor when T cells were incubated with fixed anti-CD4 antibody. Furthermore, fragmentation was detectable at 6 h after incubation when almost all of the cells were still viable as evaluated by trypan blue dye exclusion test. Cell death was prevented by addition of EGTA, cycloheximide, actinomycin D, and zinc, suggesting that the induction of cell death requires Ca2+ influx, newly synthesized protein(s), and involvement of endonuclease.

T cell receptor-mediated DNA fragmentation and cell death in T cell hybridomas

Activation of Ag-specific T cell hybridomas with a high density of immobilized anti-CD3 antibody resulted in not only secretion of IL-2 but also cell death of up to 60 to 80% in selected hybridomas after 14 h. Similar results were obtained with V beta 8+ T cell hybridomas stimulated with cross-linked F23.1 antibody. In these activated hybridomas, we found that DNA was fragmented into 180- to 200-bp multiples. DNA fragmentation was not observed when T cells were maintained after killing with anti-Thy-1 plus C or with heat treatment at 45 degrees C, nor when T cells were incubated with fixed anti-CD4 antibody. Furthermore, fragmentation was detectable at 6 h after incubation when almost all of the cells were still viable as evaluated by trypan blue dye exclusion test. Cell death was prevented by addition of EGTA, cycloheximide, actinomycin D, and zinc, suggesting that the induction of cell death requires Ca2+ influx, newly synthesized protein(s), and involvement of endonuclease.

Analysis of the molecular requirements for T cell recognition and activation by using Ia-containing lipid vesicles and stopped-flow fluorometry

Using Ia antigen-containing lipid vesicles, we investigated by stopped-flow fluorometry the requirements for helper T cell recognition and activation. When azobenzenearsonate-L-tyrosine (ABA-L-Tyr)-specific, I-Ak-restricted helper T cell hybridomas 2-45-12 were mixed with ABA-L-Tyr and purified I-Ak molecules on lipid vesicles, an increase of intercellular calcium ion concentration ([Ca2+]i) in the T cells were detected within 1-2s. The average increases of [Ca2+]i were not much different when the lipid vesicles were composed of dimyristoylphosphatidylcholine or of egg phosphatidylcholine, but they were dependent on the density of I-Ak molecules on the liposomes. The increase of [Ca2+]i was inhibited in the presence of anti-I-Ak monoclonal antibody 10.2.16, but not by the addition of anti-L3T4 monoclonal antibody GK1.5. However, the addition of anti-L3T4 antibody during the first 3 h of cultivation completely inhibited the T cell activation [interleukin (IL-2) production]. In our experimental system, IL-2 production was observed either when L3T4-positive T cell hybridomas 2-45-12 were stimulated with ABA-L-Tyr and Ia molecules on the vesicles in the presence of phorbol 12-myristate 13-acetate, or when L3T4-negative T cell hybridomas 3H60.12 were incubated with ABA-L-Tyr and Ia molecules on the planar membranes.(ABSTRACT TRUNCATED AT 250 WORDS)