Characterization of the growth factor activity of amniotic fluid on cells from hematopoietic and lymphoid organs of different life stages

We investigated the proliferation-promoting effects of murine amniotic fluid (MAF) on in vitro cultured cells originally obtained from murine hematopoietic and lymphoid organs at different life stages. MAF promoted proliferation of the fetal liver cells (FLC), newborn spleen cells and adult bone marrow cells. The proliferation-promoting activity of MAF was extended to liver cells and spleen cells from mice younger than 2 weeks old. MAF did not, however, promote the proliferation of newborn or adult thymocytes, or of spleen cells, liver cells or peritoneal cells, liver cells or peritoneal cells from 2-week-old or older mice. Rather, it partially inhibited the proliferation of spleen cells, thymocytes and peritoneal cells from 1-year-old mice. These results suggest that MAF contains growth factors for hematopoietic stem cells but not for either mature or immature T lymphocytes. Supporting this view, the MAF activity was partially neutralized by a polyclonal anti-mouse stem cell factor (SCF) antibody. Moreover, the immunoblotting of MAF against anti-mouse SCF antibody revealed a band at 30-32 kDa corresponding to the previously reported SCF. Interestingly, MAF was able to maintain FLC and adult bone marrow cells alive in culture for a relatively long time (2 weeks). The MAF activity was further shown to be partially and cell type-dependently antagonized by TNF-alpha and TGF-beta. These results provided evidence that MAF contains potentially multiple growth factors preferentially affecting the early stage of hematopoiesis, one of which is SCF.

Promotion of proliferation of murine hematopoietic stem cells by growth factors in murine amniotic fluid

It has been shown that murine amniotic fluid (MAF) displays immunosuppressive activities. We examined the effect of MAF obtained from normal mice on a murine fetal liver cell (FLC) primary culture in vitro for the detection of the possible existence of cytokines that affect hematopoiesis. MAF promoted proliferation of murine FLC and adult bone marrow cells. Proliferation-promoting activity of MAF was observed throughout the period between days 12 and 15 of pregnancy, peaking at day 12. Pooled MAF was subjected to purification procedures to isolate the active molecule(s). After ion exchange and size exclusion chromatography, one of the active molecules was shown to react with anti-mouse stem cell growth factor (SCF) antibody and the molecular weight was determined as 40-45 kDa by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot. The proliferation-promoting activity of MAF was partially neutralised by the anti-SCF antibody. These results provide evidence that MAF may contain multiple growth factors for FLC, one of which may be a unique molecule related to SCF.

Murine model of cancer gene therapy

In order to examine how the adenovirus-mediated gene therapy induce anti-adenoviral immunity, we set up experiments for a murine cancer model. We first administered adenovirus carrying LacZ (AxCALacZ) gene to DBA/2 mice intraperitoneally, then two weeks after administration of the virus, P815 tumor cells infected with adenovirus carrying LacZ gene were inoculated intraperitoneally to the AxCALacZ immune mice. The mice rejected the P815 tumor infected with AxCALacZ and survived for long periods. The peritoneal T cells in adenovirus immune mice had a strong killing effect of adenovirus-infected P815 cells. Further, parental P815 tumor cells were inoculated into the mice, which rejected the P815 tumor infected with AxCALacZ. All mice rejected P815 tumor cells and survived for long periods. These mice developed P815 specific tumor immunity, which was confirmed by a cytotoxicity assay.

Cytokine-independent proliferation of IL-2-nonproducing CTL clones in association with high TCR-signal transduction responses

Alloreactive CTL clone D2-23 proliferated in response to antigenic cells without IL-2 production. Among subclones of D2-23, the F1 but not F2 clone proliferated in response to soluble aCD3 or PMA, although both clones proliferated in response to immobilized aCD3, antigenic cells or soluble aCD3 plus costimulatory cells. The difference in responsiveness between F1 and F2 was not caused by distinct expression of CD3 or Fe receptors. Cyclosporin A, which totally blocks IL-2 production of Th1 cells, barely or only partially inhibited PMA- or aCD3-induced proliferation of F1. F1 did not produce cytokines for proliferation of F2 in response to soluble aCD3. Tyrosine phosphorylation developed for various proteins of F1 and F2 at the levels apparently correlated to the extent of cell proliferation when the cells were stimulated with soluble aCD3 or PMA. The proliferative responsiveness of F1 and F2 to the described stimulators was maintained by stimulation with IL-2 plus antigenic cells, or even IL-2 alone, but was decreased during resting culture or by stimulation with immobilized aCD3. These results show evidence of a new TCR-linked mechanism for CTL proliferation that is independent of costimulatory cell- or cytokine-mediated signaling, but is originally prepared by prior stimulation with IL-2.

Nitric oxide releasing reagent, S-nitroso-N-acetylpenicillamine, enhances the expression of manganese superoxide dismutase mRNA in rat vascular smooth muscle cells

Cultured rat vascular smooth muscle cells (VSMCs) produce nitric oxide (NO) under stimulation by lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma). NO synthase (NOS) and manganese superoxide dismutase (Mn-SOD) mRNA expressions are simultaneously induced by these stimulants in rat VSMCs. In VSMCs, S-nitroso-N-acetyl penicillamine (SNAP), one of the NO releasing reagents, induces Mn-SOD mRNA which may protect the VSMCs themselves. This suggests that NO itself may enhance the expression of Mn-SOD to protect the VSMC themselves against NO radicals in cultured rat VSMCs.

Point mutations of the c-Ki-ras gene in carcinoma and atypical epithelium associated with congenital biliary dilation

OBJECTIVES

Congenital biliary dilation (CBD) may be accompanied later by gallbladder carcinoma or bile duct carcinoma. These cancerous lesions are frequently associated with atypical epithelium that was suspected of being precancerous. To determine whether atypical epithelium may be precancerous, we examined the DNA sequence of the c-Ki-ras gene at codon 12 in nine cases of CBD concurrent with seven gallbladder carcinomas, one bile duct carcinoma, and one bile duct atypical epithelium.

METHODS

Tumor specimens were surgically removed from nine patients with CBD at Nagoya University Hospital between 1979 and 1988. Tumor was isolated by microdissection, and DNA was amplified by a two-step polymerase chain reaction which then was directly sequenced.

RESULTS

Four of seven gallbladder carcinomas and one bile duct carcinoma contained the c-Ki-ras point mutation at codon 12, and atypical epithelium associated with these carcinomas had the same mutation. One case of atypical bile duct epithelium also contained the mutation.

CONCLUSIONS

These results indicate that the c-Ki-ras point mutation at codon 12 may be responsible for either cancer or atypical epithelia associated with CBD.

Can cysteine direct tyrosine in signal transduction for environment-oriented gene control?

Signals are transduced from the cell surface to the nucleus through phosphorylation and dephosphorylation chain reactions of cellular proteins at tyrosine and serine/threonine. Recent evidence suggests that the signal generated through the protein modification at cysteine by oxidation/reduction crosstalks to the protein phosphorylation/dephosphorylation-linked one. I propose that the cysteine-oriented signal potentially directs the tyrosine-oriented one and this mechanism underlies the environment-oriented control of internal signaling for gene expression.

Amount of pollen has an effect on the systemic and local levels of soluble ICAM-1 in patients with seasonal allergic rhinitis

We investigated whether the amount of antigen has an effect on the systemic and local levels of soluble ICAM-1 (sICAM-1) in patients with pollinosis, and assessed its biologic significance. The levels of subjective symptoms and sICAM-1 in sera and nasal epithelial lining fluids (ELF) from 14 subjects with pollinosis (allergic group) and eight healthy subjects (control group) were measured from pre- to postseason in 1993 (total pollen count: 10,854/cm2) and 1994 (total pollen count: 415/cm2), and the results were compared with each other among the four groups. The levels of subjective symptoms and sICAM-1 in ELF from the allergic group significantly increased during the season in both 1993 and 1994. However, there was a significant difference (P < 0.01) between the levels of those in 1993 and those in 1994 during the season. The levels of sICAM-1 in sera from the allergic group were significantly upregulated during the seasons and postseasons only in 1993, and there was a significant difference (P < 0.05) between the levels in 1993 and those in 1994 during the postseason. We conclude that amount of pollen has an influence on the local and systemic levels of sICAM-1, as well as the scores of subjective symptoms, in patients with seasonal allergic rhinitis.

Efficient adenovirus-mediated gene transfer into human cancer cell lines derived from digestive tract

The efficiency of gene transfer into human cancer cells from digestive tract was evaluated using a replication-deficient recombinant adenovirus (Ad) vector harboring a lacZ gene of E. coli as a reporter gene (AxCALacZ). Average percent X-gal staining of esophageal cancer cell lines was 46%, that of gastric cancer cell lines 82% and that of colon cancer cell lines 70% at 3 days after Ad vector infection. X-gal staining in vitro continued 2 months after infection. By the direct injection of adenovirus vector to the tumors in nude mice, a certain percentage of tumor cells was stained by the X-gal. Colon26 cell line infected with AxCALacZ was implanted in BALB/c mice immunized with AxCALacZ, and tumor growth was suppressed. We presume this was due to anti-adenoviral immunity.

Modulation of endotoxin-induced histamine synthesis by cytokines in mouse bone marrow-derived macrophages

The aim of this study was to examine the roles of various cytokines in histamine synthesis by macrophages in bone marrow. Pure (&gt; 99% nonspecific esterase-, CD14-, and Mac-1-positive) macrophage populations were obtained after long term culture of bone marrow cells (bone marrow-derived macrophages). Culture of the cells in the presence of Escherichia coli LPS caused a slight, but dose-dependent, increase in histidine decarboxylase-associated histamine synthesis with a concomitant increase in the expression of CD14, a LPS receptor, as well as the Mac-1 Ag on their surface. Granulocyte/macrophage CSF (GM-CSF) or IL-3 strongly enhanced LPS-induced histamine formation and expression of CD14 on bone marrow-derived macrophages, without affecting the expression of Mac-1 Ag. GM-CSF and IL-3 also caused a marked accumulation of both histidine decarboxylase and IL-6 mRNAs in the cells. Macrophage CSF and IL-1-alpha also potentiated LPS-dependent histamine formation when it was stimulated with GM-CSF or IL-3. In contrast to these cytokines, IFN-gamma suppressed LPS-induced histamine production regardless of whether it was stimulated by GM-CSF or IL-3, and inhibited CD14 expression. Neither IL-6 nor granulocyte CSF had any appreciable effect on LPS-induced histamine production even in combination with GM-CSF or IL-3. These results suggest that GM-CSF and IL-3 enhance LPS-induced histamine production in bone marrow-derived macrophages and that macrophage CSF and IL-1 alpha augment the actions of GM-CSF and IL-3. Possible implication of CD14 molecule in the reactions is discussed.

Modulation of endotoxin-induced histamine synthesis by cytokines in mouse bone marrow-derived macrophages

The aim of this study was to examine the roles of various cytokines in histamine synthesis by macrophages in bone marrow. Pure (> 99% nonspecific esterase-, CD14-, and Mac-1-positive) macrophage populations were obtained after long term culture of bone marrow cells (bone marrow-derived macrophages). Culture of the cells in the presence of Escherichia coli LPS caused a slight, but dose-dependent, increase in histidine decarboxylase-associated histamine synthesis with a concomitant increase in the expression of CD14, a LPS receptor, as well as the Mac-1 Ag on their surface. Granulocyte/macrophage CSF (GM-CSF) or IL-3 strongly enhanced LPS-induced histamine formation and expression of CD14 on bone marrow-derived macrophages, without affecting the expression of Mac-1 Ag. GM-CSF and IL-3 also caused a marked accumulation of both histidine decarboxylase and IL-6 mRNAs in the cells. Macrophage CSF and IL-1-alpha also potentiated LPS-dependent histamine formation when it was stimulated with GM-CSF or IL-3. In contrast to these cytokines, IFN-gamma suppressed LPS-induced histamine production regardless of whether it was stimulated by GM-CSF or IL-3, and inhibited CD14 expression. Neither IL-6 nor granulocyte CSF had any appreciable effect on LPS-induced histamine production even in combination with GM-CSF or IL-3. These results suggest that GM-CSF and IL-3 enhance LPS-induced histamine production in bone marrow-derived macrophages and that macrophage CSF and IL-1 alpha augment the actions of GM-CSF and IL-3. Possible implication of CD14 molecule in the reactions is discussed.

Establishment of a human DAF/HRF20 double transgenic mouse line is not sufficient to suppress hyperacute rejection

To solve the chronic donor organ shortage, the pig is considered to be a possible donor candidate for human transplantation. However, hyperacute rejection occurs due to the activation of the complement cascade. Therefore, the introduction of human complement inhibitors into animal cells has been proposed as a means to prevent such exologous complement activation. To investigate the extent to which complement inhibitors are resistant to human sera in discordant animals, we established transgenic mice lines which expressed either human decay-accelerating factor (DAF) and/or homologous restriction factor 20 (HRF20) using microinjection methods. Human sera were injected into (a) 10 control mice, (b) 10 DAF-transgenic mice, (c) 10 HRF20-transgenic mice, and (d) 10 DAF and HRF20-transgenic mice. The results showed that all the mice in groups a, b, and c died immediately after injection. Three of the mice in group d died, while seven survived but showed hyperpnea and low activity. The pathological findings of groups a, b, and c included severe coagulation; however, the survivors of group d showed less severe symptoms. The above findings thus suggest that both DAF and HRF20 tend to prevent complement activation to some extent; however, its effectiveness is not considered to be sufficient for clinical use in transplantation.

Enhancement of nitric oxide production from activated macrophages by glycyrrhizin

We studied the actions of glycyrrhizin on nitric oxide production from macrophages and a macrophage cell line RAW264-7. Although glycyrrhizin did not induce nitric oxide from resting macrophages, it enhanced the production of nitric oxide from IFN-gamma activated-macrophages or RAW cells. Glycyrrhizin also enhanced the production of nitric oxide from macrophages stimulated with the supernatant of con A-activated spleen cells. Further, glycyrrhizin enhanced tumor cell killing by macrophages activated with IFN-gamma. This tumor cell killing was mainly by nitric oxide.

Inhibition of human complement-dependent cell lysis by bovine aortic endothelial cells transfected with membrane-bound complement-regulatory factor (DAF and HRF20) gene using a retroviral vector

The endothelial cells (EC) of xenografts are the target of hyperacute rejection induced by complement activation via the classical and/or the alternative pathway. To protect these cells from the attack of human complement, decay-accelerating factor (DAF, CD55) and homologous restriction factor 20 (HRF20, CD59), which belong to human complement regulatory factors, were transfected into bovine aortic EC (BAEC) using retroviral vector. Cell surface expression of DAF and HRF20 on BAEC transfectants (BAEC/DAF, BAEC/HRF20) is comparable to that on human umbilical vein EC. Phosphatidyl inositol-phospholipase C treatment diminished or abolished cell surface expression of DAF and HRF20 on BAEC. The addition of human serum to BAEC led to complement-dependent cell lysis, whereas practically no lysis was observed after addition of human serum to BAEC/DAF and BAEC/HRF20. The addition of human serum plus rabbit complement to BAEC/DAF and BAEC/HRF20 caused complement-dependent cell lysis that was comparable to that observed for BAEC. These data demonstrate that xenograft EC transfected with DAF or HRF20 cDNA using retroviral vector are protected from complement-dependent cell lysis.

Elucidation of the protein kinase C-dependent apoptosis pathway in distinct subsets of T lymphocytes in MRL-lpr/lpr mice

MRL-lpr mice are severely impaired in the Fas pathway of apoptosis induction. We here evaluate another pathway of apoptosis induction in MRL-lpr mice which is protein kinase C (PKC) dependent. Despite the defect of the Fas pathway, apoptosis developed during culture in vitro in splenic T lymphocytes from MRL-lpr mice more extensively than in T lymphocytes from MRL-(+/+) mice. Apoptosis induction in the former cells was then found to be greatly promoted by PKC inhibitor H-7, and partially prevented by PKC activator phorbol 12-myristate 13-acetate (PMA). High sensitivity to H-7, but not to PKA inhibitor HA 1004, of these cells for apoptosis induction was confirmed by detailed time course and dose-dependency experiments of the drug effect. Population analysis showed that both CD4+ T lymphocytes and CD8+ T lymphocytes from MRL-lpr mice were highly sensitive to H-7, whereas CD8+ T lymphocytes, but not CD4+ T lymphocytes, from MRL-(+/+) mice were susceptible to the reagent. Interestingly, B220+ Thy-1+ CD4-CD8- T lymphocytes from MRL-lpr mice were most sensitive to H-7 for apoptosis induction. Correspondingly, the membrane-translocated activated PKC-alpha level in splenic T lymphocytes from MRL-lpr was more extensively up-regulated by PMA than in splenic T lymphocytes from MRL-(+/+). These results suggest that some signal consistently activates PKC in MRL-lpr T lymphocytes, and this event is needed for survival of these cells. On the other hand, CD4+ CD8+ thymocytes were deleted by apoptosis in culture with PMA, whether these thymocytes were from MRL-lpr mice or MRL-(+/+) mice. This finding suggested that the apoptosis induction pathway linked to PKC activation is intact in CD4+ CD8+ thymocytes from the Fas-defective MRL-lpr mice. We conclude from these results that the PKC-dependent signal pathways for either cell death or cell activation are intact or even accelerated in lpr mice, which could both compensate for the loss of the Fas pathway and promote the generation of autoreactive T lymphocytes.

Major basic protein and topical administration of ketotifen in pollinosis under natural allergen provocation

In this study we investigated the potential relation among subjective symptoms, blood eosinophil counts and the levels of major basic protein (MBP) in serum throughout the pre- to postpollen season. In addition, we compared the effects of topical administration of ketotifen on these parameters between the prophylactic treatment group (n = 10) and the postsymptomatic treatment group (n = 10). We found that (1) the levels of MBP in serum during the season were significantly higher than those before the season and (2) the levels of the above three parameters in the prophylactic treatment group were significantly lower than those in the postsymptomatic treatment group during the season. It was concluded from these results that the action of MBP may be involved in the pathogenesis of allergic rhinitis. Furthermore, for the first time we provided evidence that topical ketotifen administration could suppress the systemic upregulation of the blood eosinophil count and MBP level in subjects with pollinosis.

Soluble ICAM-1 as a regulator of nasal allergic reaction under natural allergen provocation

BACKGROUND

Intercellular adhesion molecule-1 (ICAM-1) plays a key role in the early stage of the signal cascade leading to cellular extravasation and development of an inflammatory response. Recently, it has been reported that the soluble form of this adhesion molecule is present in human sera, possibly mediating biological actions.

OBJECTIVE

The purpose of this study was to investigate levels of soluble ICAM-1 (sICAM-1) and its receptors in patients with allergic rhinitis, and to discuss sICAM-1's biological function.

METHODS

The levels of sICAM-1 in sera and nasal epithelial lining fluids (ELF), the percentage of CD11a-positive lymphocytes in the peripheral blood, and scores of subjective symptoms from 14 patients with pollinosis (allergic group) were measured from pre- to post-season, results were compared with those from 10 non-allergic subjects (control group).

RESULTS

The levels of sICAM-1 in sera and ELF were upregulated, and CD11a-positive lymphocytes were downregulated during the in-season in the allergic group. In addition, levels of sICAM-1 sera from the allergic group remained high during the post-season, when levels of other parameters (symptoms, blood eosinophil counts, sICAM-1 in ELF and CD11a-positive lymphocytes) had roughly returned to the initial pre-season levels.

CONCLUSIONS

We demonstrate systemic and local upregulation of sICAM-1 and systemic downregulation of LFA-1 positive lymphocytes in patients with seasonal allergic rhinitis under natural allergen provocation, suggesting that sICAM-1 plays a role in regulating seasonal allergic inflammation.

Down-regulation of T-cell proliferation in response to soluble anti-CD3 antibodies through development of redirected cytolytic activity eliminating costimulatory cells

CD4+ T-depleted spleen cells (CD8+ T cells) activated by anti-CD3 antibodies (aCD3) suppressed proliferation of CD8+ T-depleted spleen cells (CD4+ T cells) and fresh normal T cells in response to aCD3. Antigen-nonspecific cytolytic activity was induced in splenic CD8+ T cells by stimulation with aCD3 and showed the peak level on day 3, whereas cytolytic activity induced in CD4+ T cells was weak. Intact Ig but not F(ab')2 of aCD3 induced and mediated cytolytic activity. Correspondingly the cytolytic activity induced by aCD3 was directed against target cells bearing Ig-binding Fc-receptor activity and cytolysis was inhibited by the addition of free Ig into the assay system. We showed that aCD3-activated T cells carried a high level of aCD3 on their surface at the time after the peak proliferation when they attained high cytolytic activity. This raised the possibility that the anti-CD3-induced aCD3-redirected cytolytic activity eliminated Fc-receptor-bearing costimulatory cells in the culture for down-regulation of the T-cell proliferation. This view was supported by partial restoration of anti-CD3-induced low responsiveness of CD8+ T cells by the addition of fresh costimulatory cells. These results suggested a new pathway of down-regulation of T-cell proliferation by aCD3-activated cytolytic CD8+ T cells.

TCR-independent induction of low responsiveness by chemically fixed cells in alloreactive CTL clones and its prevention through cognate cell-cell interaction

We established BALB/c-derived CD8+ CTL clones D2-22 (V beta 6+), D2-23 (V beta 8+) and D2-24 (V beta 8+) specific for B10.D2 minor H antigen. D2-22 and D2-23 proliferated without producing IL-2 in response to X-ray-irradiated antigenic cells, Con A, aCD3, PMA and IL-2. Paraformaldehyde-fixed antigenic spleen cells neither induced proliferation in the presence of costimulatory cells nor inhibited responses to irradiated antigenic cells added simultaneously. Unlike the previously reported results with IL-2-producing CTL clones and Th1 clones, the fixed antigenic cells failed to induce antigen-specific unresponsiveness in these IL-2-non-producing CTL clones. Instead, the responsiveness of these clones to fresh stimulation was found to be reduced severely after 2 days in the culture added with either antigenic or syngeneic fixed cells. Induction of their antigen-nonspecific low responsiveness by the fixed cells was prevented by adding irradiated syngeneic cells into the culture or even by increasing the concentration of responder D2-23 cells. Close contact of D2-23 and irradiated syngeneic cells was required to prevent the reduction of the responsiveness, although this cognate cell-cell interaction could be replaced by exogenously added IL-2 or PMA. Cytolytic and tumor cell growth inhibitory activities of D2-23 were also reduced by incubation with the fixed cells, which was prevented by the addition of irradiated syngeneic cells. These findings showed the unique properties of IL-2-nonproducing CTL clones in signal requirements for maintaining normal responsiveness for proliferation and cytolytic activity.

Dissociated control by glycyrrhizin of proliferation and IL-2 production of murine thymocytes

The action of glycyrrhizin (GL) modulating the proliferation and IL-2 production of murine thymocytes in response to anti-CD3 and concanavalin A was studied. Different from the previously reported GL effect of accelerating both IL-2 production and proliferation of mature T lymphocytes, GL displayed a dissociated action on immature thymocytes promoting IL-2 production/IL-2 receptor expression but inhibiting cell growth. Hydrocortisone-resistant mature thymocytes behaved like peripheral T lymphocytes, demonstrating the dependency of the GL action on cell maturation stage. GL-mediated growth inhibition of thymocytes was not due the cytotoxic action of GL that induces cell death or DNA fragmentation. In parallel to these dissociated actions, GL promoted the tyrosine phosphorylation of p56 but suppressed the phosphorylation of p40 induced by anti-CD3. Moreover, GL and anti-CD3 showed a combination effect suppressing the transcription of c-fos, which was promoted by anti-CD3 alone or GL alone. It is suggested that whereas mature and immature T cells share a common signal pathway for IL-2 production augmented by the action of GL, they have signaling steps for DNA synthesis which are under different mechanisms receiving the modulation effects of GL in opposite directions.

Cell type-oriented differential modulatory actions of saikosaponin-d on growth responses and DNA fragmentation of lymphocytes triggered by receptor-mediated and receptor-bypassed pathways

We examined the immunoregulatory action of saikosaponin-d (SSd), which was isolated from the root of Bupleurum talcatum L. and had a steroid-like structure, on murine thymocytes, and compared the action with that on spleen cells. Constitutive DNA synthesis or the growth response stimulated with anti-CD3mAb of thymocytes were down-regulated by 3 micrograms/ml SSd, whereas with spleen cells these were up-regulated by the same concentration of SSd. On the other hand, 3 micrograms/ml of SSd greatly up-regulated the growth response and interleukin 2 (IL-2)/interleukin 4 (IL-4) production induced through a receptor-bypassed pathway by calcium ionophore A23187 plus phorbol 12-myristate 13-acetate (PMA) in thymocytes, whereas it only slightly up-regulated them in spleen cells. Moreover, the same concentration of SSd inhibited DNA fragmentation in thymocytes induced by A23187 or PMA. These results suggest a unique cell type-dependent immuno-modulatory action of SSd.

Direct evidence of involvement of glycosylphosphatidylinositol-anchored proteins in the heavy metal-mediated signal delivery into T lymphocytes

The biological significance of the action of glycosylphosphatidylinositol (GPI)-anchored proteins in cell physiology and pathology when stimulated with their natural agonists is not known. Here we provide evidence that GPI-anchored proteins play a crucial role in the recently defined heavy metal (HgCl2)-triggered signal delivery to T lymphocytes. Thiol-reactive HgCl2, a multi-potent crosslinker of cell membrane proteins, induced heavy aggregation of Thy-1, a representative GPI-anchored protein, on murine thymocytes, and delivered a signal to induce heavy tyrosine phosphorylation of cellular proteins. This rather unusual signal delivery by HgCl2 is diminished by the pre-treatment of cells with phosphatidylinositol-specific phospholipase C, which partially cleaved GPI-anchored proteins from the cell surface. Direct evidence for the involvement of GPI or GPI-anchored proteins in the HgCl2-mediated signaling is provided by the loss of signaling in a mutant thymoma cell line defective in the phosphatidylinositol glycan-class A gene (PIG-A), and its restoration in a transfectant with PIG-A.