Administration of recombinant human IL-1 by Staphylococcus enterotoxin B prevents tolerance induction in vivo

Peripheral tolerance is important to prevent autoimmunity of T cells against tissue-specific autoantigens in peripheral organs. In certain pathologic situations, peripheral tolerance breaks for unknown reasons and autoimmune diseases occur. Anergy is one of the mechanisms of peripheral tolerance that down-modulates IL-2 synthesis and IL-4 responsiveness by helper T cell clones. In this report, we utilized a model system in which V beta 8+ CD4 T cells were anergized by administration of high doses of Staphylococcus enterotoxin B (SEB) in vivo and investigated an effect of recombinant human (rh) IL-1 on the tolerance induction. RhIL-1 was used because of its ability to induce IL-4 responsiveness in T cells. When rhIL-1 was administered within 24 h after SEB inoculation, the cytokine interfered with tolerance induction; V beta 8+CD4 T cells from mice that had been treated with both SEB and IL-1 proliferated in response to SEB and produced IL-2, IL-4, and IFN-gamma upon TCR/CD28 cross-linking. Delayed administration of rhIL-1 by 48 h failed to do this; T cells did not proliferate in response to SEB, but they retained an ability to produce IL-4 upon TCR/CD28 cross-linking. Administration of rhIL-1 induced better proliferation of V beta 8+CD4 T cells in response to SEB in vivo but did not prevent cell death after proliferation. These results suggest a potential role of inflammatory cytokine IL-1 in the course of autoimmunity via interference with tolerance.

Molecular cloning of members of the S-multigene family in self-incompatible Brassica campestris L

We isolated 12 groups of genomic clones that contained SLG-homologous regions from a genomic library constructed from an S9 homozygote of self-incompatible Brassica campestris. Both SLG9 and SRK9 genomic clones, which are located within the self-incompatibility (S) locus, were included in these groups. The promoter regions of SLG9 and SRK9 were completely identical for at least 200 bp upstream from their respective initiation codons (ATG). The five sequence elements (boxes I to V) that are conserved in the promoters of SLG and SRK genes were also found in the SLG9 and SRK9 clones. However, one conserved element (box III) unexpectedly lacked 7 of 11 bp, although box III has been considered necessary for expression in pistil. The other ten groups of genomic clones were classified into six SRK-like groups and four SLG-like groups. These results indicate that SLG, SRK, SLG-like, and SRK-like genes form a large S-multigene family in B. campestris.

Irradiation induces WAF1 expression through a p53-independent pathway in KG-1 cells

WAF1 binds to cyclin-Cdk complexes and inhibits their activity, causing cell cycle arrest. Previous studies have shown that expression of WAF1 is induced through the p53-dependent pathway; WAF1 is induced in cells with functional p53 but not in cells with either mutant p53 or no 53. Human myeloblastic leukemia cells KG-1 had no constitutive expression of p53, and irradiation did not induce p53. However, irradiation increased WAF1 expression in KG-1 cells and other cell lines containing mutant p53. The KG-1 cells constitutively produced low levels of tumor necrosis factor (TNF); irradiation markedly increased the production of TNF. Notably, induction of WAF1 mRNA by irradiation was blocked by anti-TNF antibody. Furthermore, exogenously added TNF increased levels of WAF1 mRNA in these cells. Irradiation increased the rate of WAF1 transcription 3-fold, and the half-life (t1/2) of WAF1 mRNA in these cells increased from < 1 h in unirradiated cells to > 4 h in irradiated cells. These findings indicate that increased levels of WAF1 transcripts occur, at least in part, through a pathway of TNF production and that the increase in WAF1 mRNA observed after irradiation is regulated by both transcriptional and posttranscriptional mechanisms. Our present study strongly suggests that an alternative pathway of induction of WAF1 occurs independent of activation by p53.

Immune response to hepatitis C virus core protein in mice

To analyse the immune response to the hepatitis C virus (HCV) core protein, we immunized mice with the protein. BALB/c (H-2d) and C3H/He (H-2k) mice were high responders, while C57BL/6 (H-2b) mice were low responders in terms of Th cell proliferative responses. All the strains showed comparable levels of antibody responses to the HCV core protein. The Th cell lines recognized residues 61-90 of the HCV core protein in the context of I-Ad (BALB/c) and residues 11-30 in the context of I-Ek (C3H/He), respectively. The Th cell lines were restricted by I-Ab in C57BL/6 mice but recognized no synthetic peptide that spanned the region, although derivative clones from the line recognized residues 1-20 and 91-110 of the HCV core protein, respectively. The Th cell lines were Th 1 subset in all three strains based on the profile of lymphokine secretion. The major B cell epitope of the protein was found to be within residues 21-40 of the HCV core protein in all three strains. These observations should be useful for better understanding of the immune response to the HCV core protein in vivo.

Tumor necrosis factor and interleukin-1 synergize with irradiation in expression of GM-CSF gene in human fibroblasts

Tumor necrosis factor (TNF) and interleukin-1 (IL-1) improve the survival of lethally irradiated animals through production of hematopoietic growth factors. Exposure of fibroblasts to TNF (1000 U/ml) drastically increased granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA at 1 h and the level returned nearly to baseline by 24 h. Levels of GM-CSF RNA were less than basal level at 24 h after exposure to irradiation alone. In contrast, cells cultured with TNF (1 h) and then irradiated, had prominent expression of GM-CSF mRNA at 24 h. Transcriptional run-on analysis has shown that TNF stimulated the rate of GM-CSF transcription by > 10-fold in irradiated cells. Moreover, TNF stabilized GM-CSF mRNA at 24 h after irradiation; 4 increased from < 20 min in untreated cells to > 2 h in cells cultured initially with TNF and followed by irradiation. We repeated the same experiments with IL-1 and found that IL-1 had the same effects on accumulation, transcription, and stabilization of GM-CSF RNA. Our findings indicate that TNF and IL-1 synergize with irradiation in expression of GM-CSF gene in human fibroblasts; this increased expression occurs by enhancement of transcriptional rate and post-transcriptional stabilization of GM-CSF mRNA.

Irradiation increases manganese superoxide dismutase mRNA levels in human fibroblasts. Possible mechanisms for its accumulation

Irradiation induces the production of superoxide radicals (O2.-), which play an important causative role in radiation damage. Manganese superoxide dismutase (MnSOD) is a mitochondrial enzyme involved in scavenging O2..-. This study examined MnSOD gene regulation by irradiation in WI38 human fibroblasts. Unstimulated fibroblasts constitutively expressed MnSOD activity and mRNA; irradiation markedly increased MnSOD activity and mRNA levels. The increase in MnSOD transcripts by irradiation was both time- and dose-dependent. WI38 fibroblasts constitutively produce low levels of interleukin-1 (IL-1). The induction of MnSOD mRNA by irradiation was partially blocked by anti-IL-1 antibodies, and treatment of cells with IL-1 also increased MnSOD mRNA levels. Inhibition of the cyclo-oxygenase pathway with indomethacin augmented the induction MnSOD mRNA by irradiation and prostaglandin E2 inhibited the accumulation of MnSOD mRNA by irradiation. Transcriptional run-on analysis showed that irradiation increased the rate of MnSOD transcription 2-fold. Stability studies of MnSOD mRNA in these cells showed that the half-life increased from < 1.5 h in unirradiated cells to > 4 h in irradiated cells. These results suggest that induction of the MnSOD gene after irradiation is regulated, at least in part, by IL-1 production and that increased levels of MnSOD transcripts also occur through a pathway of endogenous prostaglandin E2 production. Our data indicate that the increase in MnSOD mRNA observed after irradiation occurs through both transcriptional and post-transcriptional mechanisms.

Expression of IL-1 beta mRNA in mice after whole body X-irradiation

IL-1 beta is a stimulator of hematopoietic and inflammatory systems, and also acts as a radioprotector. After whole-body exposure to sublethal doses of ionizing radiation, the IL-1 beta mRNA level in spleen cells increases for a short time prior to regeneration of the spleen. We analyzed spleen cells of C3H/He mice after whole-body irradiation with 3 Gy x-rays to determine the cause of this short-term increase in the transcription level. An increase in the level of the message in spleen cells, found by Northern blot hybridization, reached its peak 5 to 7 days after irradiation. There was a low correlation between the curves of the mRNA level and the ratio of monocyte/macrophage lineage cells; a typical source of the message. Spleen macrophages that produce a large amount of the message were found 7 days after irradiation in an in situ hybridization experiment in which heterogeneous spleen cell populations were used. In contrast, spleen cells had no detectable levels of macrophages rich in IL-1 beta mRNA before and 17 days after irradiation. Additionally, the population of message-rich cells was 9.4% of the total number of monocytes/macrophages in the spleen. These results suggest that the short-term increase in IL-1 beta mRNA is a result of the heterogeneous differentiation of a subpopulation of spleen macrophages before regeneration of the spleen.

[Pediatric anesthesia and stress response]

The hyperglycemic and adrenocortical responses to upper and lower abdominal surgery were studied in four groups of children. In F group, lower abdominal surgery was performed under light general anesthesia (halothane 0.3-0.5% plus nitrous oxide and oxygen) combined with intravenous injections of fentanyl 10-13 micrograms.kg-1. In L-E group, lower abdominal surgery was performed under light general anesthesia combined with lumbar epidural anesthesia (intermittent injections of 1.0% lidocaine). In T-E group, upper abdominal surgery was performed under light general anesthesia combined with thoracic epidural anesthesia (intermittent injections of 1.0% lidocaine). In H group, lower abdominal surgery was performed under general anesthesia (halothane 1.0-1.5% plus nitrous oxide and oxygen). The hyperglycemic and adrenocortical responses were inhibited in F group, suggesting that intravenous injections of fentanyl 10-13 micrograms.kg-1 prevented the endocrine-metabolic response. On the other hand, in other three groups, those responses were not inhibited. Therefore we must consider the concentration and the volume of lidocaine in epidural groups. But general anesthesia combined with epidural anesthesia had a excellent effect on the postoperative pain management.

Impaired CD28-mediated co-stimulation in anergic T cells

We have investigated a CD28 co-stimulation in anergic T cells in staphylococcal enterotoxin B-inoculated mice by stimulating the cells with a plate-coated anti-TCR antibody in the presence or absence of an anti-CD28 antibody. CD28 co-stimulation increased the levels of IL-2 and IL-4 mRNAs in naive CD4+V beta 8+ T cells. However, it did not increase the levels of IL-4 mRNA at all and only partially increased those of IL-2 mRNA in anergic T cells. It was demonstrated that CD28 co-stimulation was impaired so that it no longer stabilized cytokine mRNAs in anergic cells. The levels of IL-4 mRNA in response to TCR stimulation were higher in anergic T cells than those in naive T cells in spite of the defective CD28 co-stimulation in the former cells. Anergy induction and generation of a Th2-type immune response in vivo are discussed.

Irradiation increases expression of GM-CSF in human fibroblasts by transcriptional and post-transcriptional regulation

Fibroblasts produce a variety of cytokines including granulocyte/macrophage colony-stimulating factor (GM-CSF). GM-CSF is pivotal for proliferation and function of myeloid cells. In this report, we describe the regulation of GM-CSF gene by irradiation in human fibroblasts. We found that fibroblasts constitutively produced GM-CSF; irradiation markedly increased the production of GM-CSF. The increase in GM-CSF transcripts by irradiation was both time- and dose-dependent. Moreover, irradiation increased GM-CSF mRNA in cells with prolonged exposure to 12-O-tetradecanoyl-phorbol-13-acetate (TPA). WI38 fibroblasts constitutively produce low levels of IL-1. Induction of GM-CSF mRNA by irradiation was partially blocked by anti-IL-1 antibodies. On the other hand, inhibition of prostaglandin synthesis did not affect induction of GM-CSF RNA. Transcriptional run-on analysis showed that irradiation increased the rate of GM-CSF transcription. Stability studies of GM-CSF mRNA in these cells showed that half-life (t1/2) increased from < 20 min in unirradiated cells to > 100 min in irradiated cells. These findings suggest that the increase in GM-CSF mRNA observed after irradiation is regulated by transcriptional and post-transcriptional mechanisms. Our results indicate that induction of GM-CSF gene by irradiation requires de novo protein synthesis and increased levels of GM-CSF transcripts also occur through a pathway distinct from protein kinase C activation.

Characterization of p59fyn-mediated signal transduction on T cell activation

Protein tyrosine kinase p59fyn is associated with the TCR-CD3 complex and is suggested to play a role in T cell activation. To determine the molecular mechanism of p59fyn-mediated signal transduction in T cell activation, we established murine T cell hybridoma lines that expressed an elevated amount of wild-type or mutant fyns. Clones that expressed high levels of normal p59fyn and active p59fyn, encoded by wild-type and f-14 mutant fyn respectively, showed enhanced IL-2 production upon stimulation by anti-CD3 antibodies or natural antigen. On the other hand, clones that expressed kinase negative p59fyn and p59fyn with an SH2 (Src-homology 2) deletion encoded by t-1 mutant fyn showed little induction of IL-2 production upon stimulation. These data suggest that p59fyn is important in T cell signaling and that the SH2 sequence plays a critical role in the reaction. Induction of tyrosine phosphorylation of multiple proteins upon antigenic stimulation was augmented similarly in the cells that respectively expressed wild-type and f-14 mutant fyns at elevated levels. The proteins that became highly tyrosine-phosphorylated included phospholipase C (PLC-gamma 1), p95vav, ZAP-70, the MAP kinase, CD3 zeta and unidentified proteins of 120, 100 and 80 kDa. Tyrosine phosphorylation of the 120, 95 and 68 kDa proteins associated with PLC-gamma 1 was also observed in these cells upon stimulation. In contrast, only the 100 kDa protein and the MAP kinase were increasingly tyrosine phosphorylated in the antigen-stimulated cells expressing t-1 fyn. These data suggest that PLC-gamma 1, PLC-gamma 1 associated molecules, p95vav, the 80 kDa protein, ZAP-70 and the CD3 zeta chain may be substrates of p59fyn or of other tyrosine kinases regulated by p59fyn and be important in T cell signaling.

In vitro effects of OK-432 on irradiated mouse bone marrow cells

PURPOSE

In vitro effects of OK-432 on irradiated mouse bone marrow cells are examined.

METHODS AND MATERIALS

Bone marrow cells of BDF1 mouse (1 x 10(6) cells/ml) were incubated with alpha medium, 2% fetal calf serum and OK-432 in a CO2 incubator at 37 degrees C for 24, 48 and 72 h, respectively. After centrifugation, each supernatant was collected and used for conditioned medium in CFU-GM assay: Changes in CFU-GM as a function of incubation time and OK-432 dose was examined; changes of CFU-GM according to various doses of OK-432 were examined in two mouse strains, BDF1 and BALB/c mouse; changes in protective effect of OK-432 in terms of CFU-GM as a function of administration timing of OK-432 in relation to irradiation. As a radiation source, 137Cs at a dose rate of 500 cGy/min was used.

RESULTS

The CFU-GM decreased with the incubation time when OK-432 was not administered, while it significantly increased with incubation time when OK-432 was added at 0.5 and 1.0 KE/ml at 48-72 h of incubation. The former showed marked increase at 48-72 h of incubation. CFU-GM of BDF1 mouse was always higher than that of BALB/c mouse for any dose of OK-432. CFU-GM per femur according to the timing of administration of OK-432 from 24 h before to 24 h after irradiation showed 10299 +/- 2300 (24 h before), 10783 +/- 2463 (3 h before), 10045 +/- 1501 (immediately after), 8504 +/- 1188 (3 h after), 4898 +/- 1212 (6 h after), 1214 +/- 736 (12 h after) and 181 +/- 113 (24 h after irradiation), respectively.

CONCLUSION

OK-432 stimulates cultured mouse bone marrow cells to produce GM-CSF in vitro by direct contact action. This direct stimulating action of OK-432 on GM-CSF production of bone marrow cells can be kept from 24 h before to at least 3 h after irradiation.

Number and location of AUUUA motifs: role in regulating transiently expressed RNAs

Many RNAs coding for either cytokines or oncogenes are unstable and have a short half-life (t1/2). The AUUUA motif is a highly conserved sequence and is repeated three or more times in the 3' untranslated region (3'UTR) of RNAs encoding many of these short-lived cytokines and oncogenes. These sequences can confer instability. In this study, we investigated the role of number and location of AUUUA motifs in stabilization of RNA. We introduced 1xATTTA, 2xATTTA, ATTTTTTTA (second adenosine of 2xATTTA was substituted with a thymidine), 3xATTTA, 5xATTTA, 7xATTTA [AT-rich sequence from granulocyte-macrophage colony-stimulating factor [GM-CSF] gene (AT-62)], and GC-62 (GC sequences were substituted for ATTTA sequences in the 7xATTTA) into the 3'UTR of rabbit beta-globin (R beta G) gene. This construct also contained the neomycin-resistance gene. These expression vectors were transfected into human lung fibroblasts (W138), which constitutively expressed low levels of GM-CSF mRNA. Stable transfectants were selected by growth in G418. Northern blot analysis of actinomycin D-treated, stably transfected cells demonstrated that the number of AUUUA sequences correlated with rapidity of turnover of the chimeric R beta G mRNA. The rank order of stability was GC-62 = 1xATTTA = 2xATTTA (no RNA decay at 4 hours) > 3xATTTA = 5xATTTA (t1/2, 4 hours) > 7xATTTA (t1/2, 2 hours). Stability of mRNA of R beta G also was reduced (t1/2, 2 to 4 hours) when AT-62 was introduced into the second exon of R beta G gene. In these same cells, the t1/2 of GM-CSF RNA was approximately 10 to 15 minutes, suggesting that the AUUUA motifs cannot alone account for the rapid degradation of this cytokine mRNA. Phorbol diesters, including 12-0-tetradecanoyl phorbol 13-acetate (TPA), stabilize a variety of transiently expressed RNAs, including GM-CSF RNA. We found that TPA markedly increased (> 30-fold) the accumulation of GM-CSF RNA. In contrast, TPA was unable to stimulate the levels of the chimeric R beta G when either 1x, 2x, 3x, or 5xATTTA motifs were fused to 3'UTR, or when either AT-62 or GC-62 control sequences were fused to the second exon. The chimeric beta-globin construct with either AT-62 or ATTTTTTTA in the 3'UTR had only an approximately twofold to threefold increase in accumulation.(ABSTRACT TRUNCATED AT 400 WORDS)

[Perioperative management of pediatric patient with vena cava superior thrombosis complicated with nephrotic syndrome]

Nephrotic syndrome is a disease which accompanies hypoproteinemia, edema, hyperlipidemia and coagulopathy. This syndrome has also been recognized in pediatric patient. We experienced recently a case of 11-year-old girl, who had insertion of a plasma exchange catheter because of secondary hyperlipidemia due to nephrotic syndrome. She suffered soon from a severe SVC obstruction by thrombosis grown up around the catheter and an emergency thrombectomy was planned under the cardiopulmonary bypass. Renal function was maintained preoperatively, in comparison with nephrotic syndrome in adult where some problems in perioperative management, such as difficulties in tracheal intubation, choice of anesthetic drugs, blood and fluid management, monitoring without CVP and weaning from ventilator are observed. Induction was carried out carefully under spontaneous breathing and the anesthetic method we used consisted of balanced technique using N2O, O2, fentanyl and pancuronium bromide with moderate hyperventilation. Intraoperative course was uneventful and the patient was extubated on the second day after the operation without any neurological defects.

Radiosensitivity of CD45RO+ memory and CD45RO- naive T cells in culture

Radiosensitivities of various human T-cell subsets were investigated by a proliferation assay and by a single-cell gel electrophoresis assay. Each T-cell subset was purified using a cell sorter and was induced to proliferate by ionomycin and interleukin 2. Unsorted T cells showed biphasic dose-survival curves, indicating the heterogeneity of T cells in terms of radiosensitivity. Purified CD4+ helper and CD8+ killer T cells showed similar biphasic dose-survival curves. Hence both T-cell subsets were composed of cells of different radiosensitivity. The T-cell subsets belonging to different activation stages such as CD45RO+ memory and CD45RO- naive T cells had different dose-survival curves. The former was more radiosensitive than the latter. The high radiosensitivity of CD45RO+ cells was also demonstrated by single-cell gel electrophoresis after irradiation. This is the first demonstration that a particular cell surface marker on T cells is correlated with greater radiosensitivity.

Effect of human recombinant granulocyte colony-stimulating factor on induction of myeloid leukemias by X-irradiation in mice

Hematopoietic suppression is one of the serious problems induced by whole body irradiation. Granulocyte colony-stimulating factor (G-CSF) stimulates the progenitors of granulocytes and accelerates their recovery from bone marrow suppression induced by cytotoxic chemotherapy or radiation. On the other hand, G-CSF stimulates proliferation of myeloid leukemia cells as well as normal granulocytes in vitro. We designed a method to determine if G-CSF affects the incidence of myeloid leukemias induced by irradiation and the types of leukemias induced according to the French-American-British (FAB) classification in RFM/MsNrs mice. Administration of G-CSF (2 micrograms/d for 7 days) after a single 3-Gy irradiation significantly increased the number of peripheral blood neutrophils as compared with those in control mice. Even after discontinuation of G-CSF, both the total leukocyte and neutrophil counts increased to day 10, and their levels remained elevated until day 14. The incidence of myeloid leukemia in mice exposed to a single 3-Gy irradiation was 18.6% (38 of 204), and treatment with G-CSF did not increase the incidence (15.7% [32 of 204]). In the mice with radiation-induced leukemia, those receiving G-CSF had a mean survival time of 357 days, whereas those not receiving the factor survived for 349 days. There was no significant difference of survivals between the two groups. Most of the radiation-induced leukemias in the two groups were M1 or M2, according to the FAB classification; no characteristic difference was observed among the types of leukemias. Although G-CSF stimulated the leukemia cells in vitro, G-CSF administration after irradiation did not increase the occurrence of radiation-induced myeloid leukemias. Our results show that administration of G-CSF effectively accelerates neutrophil recovery from irradiation-induced hematopoietic injury and does not enhance the induction of myeloid leukemia in RFM/MsNrs mice by irradiation.

The role of macrophages in antigen presentation and T cell tolerance

Bone marrow derived cells (dendritic cells, macrophages and B cells) are involved in antigen presentation and T cell tolerance. However, the precise functions of each cell type remain unclear. To determine the role of macrophages we produced transgenic mice expressing I-E molecules only on macrophages, by introducing the hybrid gene containing the colony stimulating factor-1 (CSF-1) receptor promoter region and the structural gene encoding E alpha d into C57BL/6 mice. In these mice I-E restricted antigen presentation and T cell priming were impaired. With respect to T cell tolerance, I-E reactive T cells were anergized but not clonally deleted. These results clearly demonstrate that macrophages by themselves are defective in efficient I-E restricted antigen presentation, so that T cells exposed to antigens expressed on macrophages are led to anergy.

Effects of different doses of thiopentone on the increase in serum myoglobin induced by suxamethonium in children

We have studied the effects of different doses of thiopentone on the increase in serum myoglobin after administration of suxamethonium during inhalation induction of anaesthesia in children. Forty-three children were anaesthetized with halothane and nitrous oxide in oxygen and allocated to four groups: group S received suxamethonium 1 mg kg-1 to facilitate intubation; group ST2 received thiopentone 2 mg kg-1 and group ST4 received thiopentone 4 mg kg-1, before administration of suxamethonium 1 mg kg-1; group N did not receive thiopentone or suxamethonium. Serum myoglobin and creatine kinase (CK) concentrations were measured until 60 min after the injection of suxamethonium. Both myoglobin and CK concentrations increased in the three groups receiving suxamethonium. There were no significant differences between groups S and ST2, but the myoglobin concentration was less in group ST4 than in groups S and ST2. A significant difference in CK concentration was found only between groups ST2 and ST4 at 60 min. In group N, both values remained reasonably constant. Thiopentone 4 mg kg-1, but not 2 mg kg-1, attenuated the increase. The results indicate that to prevent a marked elevation in serum myoglobin after administration of suxamethonium, thiopentone 4 mg kg-1 should be administered.

Irreversible suppression of CD8 expression in CD4-CD8+ thymocytes upon in vitro stimulation

CD8 (Ly-2) expression was suppressed in purified murine CD4-CD8+ thymocytes at the mRNA level upon continuous stimulation with PMA and ionomycin in the presence of rIL-2. The level of CD8 expression on CD4-CD8+ thymocytes was reduced gradually during the culture and a majority of them turned into CD4-CD8- cells after 48 hr. This suppression was not transient, since CD8 expression was not recovered on these cells in additional 48 hr of culture without PMA and ionomycin. The suppression was dependent on the concentrations of PMA and ionomycin, and inhibited by adding an immunosuppressant, CsA to the culture. Treatment with either PMA or ionomycin alone did not induce suppression of CD8. Crosslinking of CD3-epsilon chains also induced suppression of CD8 for a part of CD4-CD8+ thymocytes. Interestingly, CD8 expression was hardly suppressed in CD4-CD8+ peripheral T lymphocytes, suggesting that the mechanisms of suppression of CD8 is developmentally regulated. We propose that the suppression of CD8 expression at CD4-CD8+ stage involves an additional mechanism of negative selection of thymic T cells.

[Effect of succinylcholine on serum potassium concentration in children with chronic renal failure]

Serum potassium (K+) levels were measured after intravenous injection of succinylcholine (SCh) in 10 children with chronic renal failure, 10 normal children aged 1 to 10 years and 10 children with chronic renal failure after pretreatment with pancuronium prior to SCh. Arterial blood gas was maintained within normal ranges. The serum K+ level increased significantly during 10 minutes after SCh in normal children. There was no significant difference between serum K+ levels in normal children and those in children with chronic renal failure. Administration of pancuronium in small doses (20 micrograms.kg-1) prior to SCh (1 mg.kg-1) was not effective to prevent serum K+ elevation completely. Our results indicate that the administration of SCh in children with chronic renal failure might be possible without increasing serum potassium level.

Irradiation increases levels of GM-CSF through RNA stabilization which requires an AU-rich region in cancer cells

Granulocyte/macrophage colony stimulating factor (GM-CSF) is a hematopoietic growth factor that stimulates a wide range of myeloid hematopoietic cells; RNAs coding for many oncogenes and cytokines including GM-CSF have a very short half-life. The motif of AUUUA is a highly conserved sequence in the 3'untranslated regions (3'UTR) of these transcripts and is repeated a number of times in these short-lived cytokines and oncogenes. These sequences play a major role in controlling stability of these transcripts. Human cancer cells were transfected with a chimeric rabbit beta-globin gene linked to either a 58 bp sequence of the AT-rich region from GM-CSF or a control sequence. We have found that irradiation stimulates accumulation of GM-CSF, interleukin-6 (IL-6), and IL-1 beta RNAs. In addition, this accumulation of GM-CSF was at least, in part, a result of increased stabilization of GM-CSF transcripts. Further experiments showed that irradiation increased levels of the chimeric beta-globin transcripts containing AUUUA sequences from GM-CSF, but not those containing the control sequences. Our results suggest that irradiation increases expression of GM-CSF RNA and that posttranscriptional stabilization requiring AUUUA sequences probably is in part one of the mechanisms producing the increased levels of GM-CSF RNA by irradiation.

Isolation of Getah virus from dead fetuses extracted from a naturally infected sow in Japan

Three viruses producing a cytopathic effect in cell culture were isolated from dead fetuses extracted from a naturally infected sow, and were found to be serologically identical by neutralization tests. One of the viruses was cloned and named the Sakura strain. The Sakura strain was identified as Getah virus by cross-neutralization tests.

Tolerogenic ability of thymocytes in organ-cultured thymus lobes

It is generally believed that macrophages and dendritic cells are the major cell populations that present tolerogenic self antigens to developing thymocytes. However, it is still controversial whether self antigens expressed on thymocytes themselves work as tolerogens in the thymus. To evaluate this possibility, Thy-1 bright cells were sorted out from fetal thymus cells on the 15th gestation day, and were colonized into 2'-deoxyguanosine-treated allogeneic thymus lobes. The repopulated thymus lobes were organ-cultured, and the allo-specific killer activity of thymocytes recovered from the lobes was examined. These cells were tolerant to class I but not to class II-MHC of the donor haplotype, indicating that class I molecules expressed on the thymocytes worked as tolerogen. Tolerogenic ability of Thy-1+ cells was also demonstrated in another system. Upon intimate contact with allogeneic thymus lobes on a polycarbonate filter, thymus lobes fused with each other and Thy-1+ cells co-migrated (Eur. J. Immunol. 19:1525-1530, 1989). In thymus lobes rendered parabiotic from day 5, CTL tolerance was achieved against class I but not to class II MHC. These data indicate that thymocyte-thymocyte interaction is sufficient to induce class I CTL tolerance in developing thymocytes.

Tolerogenic ability of thymocytes in organ-cultured thymus lobes

It is generally believed that macrophages and dendritic cells are the major cell populations that present tolerogenic self antigens to developing thymocytes. However, it is still controversial whether self antigens expressed on thymocytes themselves work as tolerogens in the thymus. To evaluate this possibility, Thy-1 bright cells were sorted out from fetal thymus cells on the 15th gestation day, and were colonized into 2'-deoxyguanosine-treated allogeneic thymus lobes. The repopulated thymus lobes were organ-cultured, and the allo-specific killer activity of thymocytes recovered from the lobes was examined. These cells were tolerant to class I but not to class II-MHC of the donor haplotype, indicating that class I molecules expressed on the thymocytes worked as tolerogen. Tolerogenic ability of Thy-1+ cells was also demonstrated in another system. Upon intimate contact with allogeneic thymus lobes on a polycarbonate filter, thymus lobes fused with each other and Thy-1+ cells co-migrated (Eur. J. Immunol. 19:1525-1530, 1989). In thymus lobes rendered parabiotic from day 5, CTL tolerance was achieved against class I but not to class II MHC. These data indicate that thymocyte-thymocyte interaction is sufficient to induce class I CTL tolerance in developing thymocytes.

Biochemical characterization and tissue distribution of hamster complement C1s

Several mAb (PG11, NG7, and ED4) against hamster complement C1s were obtained. PG11 and NG7 were shown to cross-react with human and rat C1s. By using an immunohistochemical method, we examined localization of C1s in tissues of hamsters and rats. Present results revealed a widespread yet specific staining of hamster C1s which is associated with endoderm-, mesoderm-, and neuroectoderm-derived cells. For example, chondrocyte of hyaline cartilage and surface epithelium of the stomach were strongly positive. Intestinal epithelium, muscle cells, pia mater and epithelium of the choroid plexus of the ventricle, and hepatocytes were also stained. The synthesis of hamster C1s in these organs was confirmed by RNA blot hybridization. Secretion of C1s into the culture medium was revealed by immunoblot analysis in cell lines of hepatocytes, kidney cells, and myoblasts of rat or hamster.

Biochemical characterization and tissue distribution of hamster complement C1s

Several mAb (PG11, NG7, and ED4) against hamster complement C1s were obtained. PG11 and NG7 were shown to cross-react with human and rat C1s. By using an immunohistochemical method, we examined localization of C1s in tissues of hamsters and rats. Present results revealed a widespread yet specific staining of hamster C1s which is associated with endoderm-, mesoderm-, and neuroectoderm-derived cells. For example, chondrocyte of hyaline cartilage and surface epithelium of the stomach were strongly positive. Intestinal epithelium, muscle cells, pia mater and epithelium of the choroid plexus of the ventricle, and hepatocytes were also stained. The synthesis of hamster C1s in these organs was confirmed by RNA blot hybridization. Secretion of C1s into the culture medium was revealed by immunoblot analysis in cell lines of hepatocytes, kidney cells, and myoblasts of rat or hamster.

[Effects of succinylcholine on serum levels of myoglobin and CK in children under halothane or enflurane anesthesia]

We studied the effects of succinylcholine (SCC) on serum levels of myoglobin (Mb) and CK in children under halothane or enflurane anesthesia. Forty-five children, aged 2 years 11 months to 12 years 6 months were subjected to this study. They were divided into four groups; the two groups were injected with SCC 1 mg.kg-1 intravenously to facilitate tracheal intubation and maintained with halothane (Group SH) or with enflurane (Group SE). The other two groups were intubated without the aid of SCC and maintained with halothane (Group H), or with enflurane (Group E). Mb was analyzed by an antibody radioimmunoassay technique and CK was analyzed by a modified Rosalki's method. While Mb increased in all four groups, the increase was pronounced in the SCC groups (60 min value of Group SH 2192 +/- 639 ng.ml-1, Group SE 1722 +/- 436 ng.ml-1, mean +/- SE), and the increase was significantly smaller in SCC free groups (Group H 40 +/- 12 ng.ml-1, Group E 43 +/- 9 ng.ml-1). The CK value increased only in the SCC groups to 174.1 +/- 32.8 IU.l-1 in Group SH, and to 193.6 +/- 35.7 IU.l-1 in Group SE at 60 min, respectively. These results indicate that increases in Mb and CK values were mainly induced by SCC injection and that SCC might play some roles in development of malignant hyperthermia.

[Cell proliferation in a triple gastric cancer--a study using the isolated organ perfusion system]

So as to study the cell proliferation in a case with triple gastric cancers, we labeled an operated whole stomach with bromodeoxyuridine (BrdU) by the isolated organ perfusion system using artificial blood. Anti-BrdU immunohistochemical staining of sections from every part of the stomach was performed, and 3 separated cancerous lesions were all diagnosed as well differentiated adenocarcinomas. The labeling index (L.I.) of the cancerous lesions were found to differ from part to part. However, the L.I. tended to be higher in the superficial mucosal areas and in the cell-dense areas of the submucosa. In the almost normal fundic glands, the labeled zone was localized in the neck of the glands. The more metaplastic gastritis was advanced, the more the labeled zone shifted irregularly toward the bottom of the glands. Whenever the interstinal metaplasia was completed, the labeled zone was localized in the bottom of the glands. This method was found useful in studying the cell proliferation in the stomach without causing any harm to the human body.

The natural history of multiple endocrine neoplasia type 2A--a clinical analysis

The records of 18 patients with multiple endocrine neoplasia (MEN) type 2A in a family consisting of 87 members in 5 generations, were reviewed with respect to age at onset and length of survival in a study of the natural history of this syndrome. Of these 18 patients, 8 were alive following surgical treatment, while 10 had died without treatment. The clinical onset of medullary thyroid carcinoma was noticed as a nodule in the neck at between 17 and 34 years of age (mean 24 years); the onset of pheochromocytoma was characterized by palpitation, hypertensive attacks or recurrent headache at between 17 and 42 years of age (mean 27 years); and death occurred in 10 patients at between 23 and 67 years of age (mean 40.6 years). This information on the age at onset of individual clinical manifestations, and on the length of survival of gene carriers, may be useful for clinicians who are asked to assess the risk of the development of this syndrome in a genetically predisposed asymptomatic individual, because screening tests are often refused by members of Japanese families with MEN type 2A.

[A case report of five-year survival with repeated resection of metastases from jejunal leiomyosarcoma]

A case of five-year survival of jejunal leiomyosarcoma with metastases to the liver and mesentery treated with four times surgery was reported here. Four metastatic lesions were detected in the sigmoid mesocolon once and in the liver three times and resected with hope of cure. The patient, a 37 years old male, tolerated surgical procedures including an extended right hepatic lobectomy and recovered each time. He is leading a satisfactory daily life 5 years and 3 months after the initial operation although multiple liver metastases were detected 10 months after the fourth operation. A positive surgical therapy is advocated in selected patients who have spreading leiomyosarcoma of the bowel.

T cell clones are killed by a thymic stromal cell monolayer following stimulation of T cell receptor with antigen and/or H-2 molecules on the monolayer

A thymic stromal cell clone, MRL104.8a, expressed class I and class II H-2k antigens after exposure to gamma-interferon (gamma-IFN) and produced thymic stroma-derived T cell growth factor (TSTGF) irrespective of gamma-IFN exposure. Culturing the keyhole limpet hemocyanin (KLH)-specific, I-Ek-restricted 9-16 helper T cell (Th) clone on an Ia (I-Ak and I-Ek)-expressing MRL 104.8a monolayer induced potent proliferation of the 9-16 cells by virtue of the TSTGF produced by the monolayer. In contrast, the addition of KLH to cultures resulted in lethal growth inhibition of the 9-16 Th clone. Such a phenomenon was also observed for various Th as well as cytotoxic T lymphocyte (CTL) clones, and the following were revealed: (i) the growth of the ovalbumin (OVA)-or bovine thyroglobulin (BTg)-specific Th clone on the la-expressing MRL 104.8a monolayer was also inhibited by addition of the relevant antigen. The fact that these Th clones required antigen-presenting cells (APC) capable of processing antigen for the recognition of the respective target antigen suggested the potential of MRL 104.8a cells for antigen-processing; (ii) the lethal growth inhibition of KLH-specific, I-Ak (23-1-8)- or I-Ek (9-16)-restricted Th clone was prevented selectively by anti-I-Ak or anti-I-Ek antibody respectively; (iii) the I-Ek-alloreactive Th clone (2-13) was supported for its growth on a gamma-IFN-unexposed MRL 104.8a monolayer, whereas this clone was killed on an I-Ek-expressing monolayer; and (iv) when I-Ak-reactive CTL clones were cultured on an Ia- or Ia+ monolayer, CTL clones failed to exhibit cytotoxic effect on either the Ia- or the Ia+ monolayer, but were conversely killed by the Ia+ monolayer. Its killing was also prevented by an antibody which inhibits the recognition of Ia antigen on the monolayer by CTL clones.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cyclosporine A on thymocyte differentiation in fetal thymus organ culture

During the course of differentiation in the thymus, precursor T cells are negatively selected by a self-tolerance mechanism or positively selected to acquire restriction specificity to self major histocompatibility complexes. We investigated the process of T cell differentiation and those selections using a fetal thymus organ culture with or without cyclosporine A. The agent blocked the maturation step from CD4+8+ double positive cells to mature CD4-8+ or CD4+8- single positive cells. On the other hand, the agent did not inhibit the development of CD3+4-8- T cell receptor (TCR)alpha beta- cells, which were supposed to be T cells bearing gamma delta-TCR chains. These results suggest that the development of thymocytes bearing alpha beta- or gamma delta-TCR chains differ in requirement for thymocyte-stromal cell interaction.

Tolerance induction in the organ-cultured thymus lobes upon intimate contact with allogeneic thymus lobes

In an organ-cultured murine fetus thymus, precursor cytotoxic T lymphocytes (pCTL) specific for alloantigens developed successfully but those reactive with self antigens were eliminated. In attempting to dissect the mechanism of self tolerance, intrathymic chimera was made by culturing two genetically disparate thymuses in close contact with each other (parabiosis of thymuses). This maneuver resulted in the induction of specific and mutual CTL tolerance. It seems that CTL tolerance was induced by clonal deletion but not by active suppression. Since 2'-deoxyguanosine treatment abolished the tolerogenic capability of the thymus, hemopoietic cells capable of migrating to and fro in the parabiotic thymuses are thought to be responsible for tolerance induction. Induction of CTL tolerance was dependent on the maturation stages of T cells in the thymus: T cells in 5-day-, but not in 7-day-cultured thymuses were susceptible to tolerance induction, indicating that T cells expressing T cell receptors at low density are susceptible to tolerance induction.

Split tolerance in nude mice transplanted with 2'-deoxyguanosine-treated allogeneic thymus lobes

To elucidate the acquisition of self tolerance in the thymus, full-allogeneic thymic chimeras were constructed. Athymic C3H and BALB/c nude mice were reconstituted with the thymic lobes of BALB/c and B10.BR fetuses, respectively, that were organ cultured for 5 days in the presence of 2'-deoxyguanosine. T cells in these chimeras were tolerized to the host MHC in both MLR and CTL assays. In contrast, T cells in the chimeras exhibited split tolerance for the thymic MHC haplotype. CTL specific for class I MHC of the thymic haplotype were generated not only from the peripheral T cells of the chimeras but also from thymocytes re-populated in the engrafted thymic lobes. However, T cells in these chimeras responded poorly to the class II MHC of the thymic haplotype in a standard MLR assay. In a syngeneic MLR culture upon stimulation with enriched APC of the thymic haplotype, only 22 to 48% of the responses were mediated by CD4+ cells, and proliferations of CD4- cells were prominent. There were no haplotype-specific suppressor cells detected which would cause the unresponsiveness to the thymic class II MHC. These results indicated that the thymic lobes treated with 2'-deoxyguanosine were defective in the ability to induce the transplantation tolerance for the class I MHC expressed on the thymus, although the same thymic lobes were able to induce the transplantation tolerance for the thymic class II MHC.

Split tolerance in nude mice transplanted with 2'-deoxyguanosine-treated allogeneic thymus lobes

To elucidate the acquisition of self tolerance in the thymus, full-allogeneic thymic chimeras were constructed. Athymic C3H and BALB/c nude mice were reconstituted with the thymic lobes of BALB/c and B10.BR fetuses, respectively, that were organ cultured for 5 days in the presence of 2'-deoxyguanosine. T cells in these chimeras were tolerized to the host MHC in both MLR and CTL assays. In contrast, T cells in the chimeras exhibited split tolerance for the thymic MHC haplotype. CTL specific for class I MHC of the thymic haplotype were generated not only from the peripheral T cells of the chimeras but also from thymocytes re-populated in the engrafted thymic lobes. However, T cells in these chimeras responded poorly to the class II MHC of the thymic haplotype in a standard MLR assay. In a syngeneic MLR culture upon stimulation with enriched APC of the thymic haplotype, only 22 to 48% of the responses were mediated by CD4+ cells, and proliferations of CD4- cells were prominent. There were no haplotype-specific suppressor cells detected which would cause the unresponsiveness to the thymic class II MHC. These results indicated that the thymic lobes treated with 2'-deoxyguanosine were defective in the ability to induce the transplantation tolerance for the class I MHC expressed on the thymus, although the same thymic lobes were able to induce the transplantation tolerance for the thymic class II MHC.

Cyclosporin A and anti-Ia antibody cause a maturation defect of CD4+8- cells in organ-cultured fetal thymus

The effects of anti-Ia antibodies and cyclosporin A (CsA) on phenotypic differentiation of murine thymocytes were assessed in organ-cultured fetal thymuses. Both agents specifically abrogated the generation of CD4+8- thymocytes. Immunohistochemical studies revealed that Ia antigen on the organ-cultured thymic epithelial cells did not disappear with the addition of the agents, although anti-Ia antibody was proved to bind to Ia antigen during the culture. On the other hand, CsA neither changed the expression of Ia nor bound to it. As CsA is known to block the signalling cascade initiated by perturbation of T-cell receptor (TcR), it is suggested that both the Ia expression in the thymus and the signalling via receptors on thymocytes, the signals presumably generated by TcR binding to class II MHC molecules, might be necessary for phenotypic differentiation of class II MHC-restricted T cells (CD4+8- cells), but not for class I MHC-restricted T cells (CD4-8+).

Immunotherapy of hepatocellular carcinoma with autologous lymphokine-activated killer cells and/or recombinant interleukin-2

Five patients with hepatocellular carcinoma were subjected to immunotherapy: three patients were treated by adoptive immunotherapy with lymphokine-activated killer (LAK) cells and recombinant interleukin-2 (rIL-2), and two patients by systemic administration of rIL-2 alone. In one patient with diffuse-type hepatocellular carcinoma and portal vein thrombosis who was treated by infusion of LAK cells (a total number of 1.5 x 10(10) cells/13 doses) and continuous rIL-2 administration (a total dose of 1.25 x 10(8) units) via a percutaneously placed hepatic arterial catheter, the size of the tumor reduced dramatically and the portal vein thrombosis retracted. In two patients who had LAK cells infused (totals of 6.6 x 10(9) cells/4 doses and 3.1 x 10(9) cells/2 doses, respectively) during hepatic angiogram followed by systemic administration of rIL-2 twice a day, no clinical improvement was noticed. In two patients who received rIL-2 alone systemically (total doses of 8.9 x 10(7) and 5.5 x 10(7) units, respectively), neither clinical improvement nor severe side effects were observed. The results suggest that adoptive immunotherapy combined with continuous local administration of rIL-2 via a percutaneously placed hepatic arterial catheter may be an effective therapy without apparent side effects for patients with hepatocellular carcinoma who cannot be treated by conventional cancer therapy.

Antigen-induced suppression of the proliferative response of T cell clones

Proliferation of Ag-specific T cell clones can be inhibited by the addition of high concentrations of Ag at the beginning of culture. Under these conditions the cells produce lymphokines and express high affinity IL-2R but fail to divide, even after the addition of exogenous IL-2. This state results from restimulation of the cells with Ag-Ia molecule complexes approximately 20 h after initiation of culture. It can be prevented by addition of either an anti-Ia or an anti-L3T4 mAb at that time, but not by cyclosporin A, and mimicked in cultures containing low concentrations of antigen by addition at that time of high Ag concentrations or normal stimulatory concentrations of Con A. These observations suggest that restimulation of activated T cell clones 20 h after their initial stimulation prevents them from dividing.

Antigen-induced suppression of the proliferative response of T cell clones

Proliferation of Ag-specific T cell clones can be inhibited by the addition of high concentrations of Ag at the beginning of culture. Under these conditions the cells produce lymphokines and express high affinity IL-2R but fail to divide, even after the addition of exogenous IL-2. This state results from restimulation of the cells with Ag-Ia molecule complexes approximately 20 h after initiation of culture. It can be prevented by addition of either an anti-Ia or an anti-L3T4 mAb at that time, but not by cyclosporin A, and mimicked in cultures containing low concentrations of antigen by addition at that time of high Ag concentrations or normal stimulatory concentrations of Con A. These observations suggest that restimulation of activated T cell clones 20 h after their initial stimulation prevents them from dividing.

Induction of anomalous killing activity from antigen-specific CTL clones by adding high doses of human recombinant interleukin 2

Four out of six long-term murine cytotoxic T lymphocyte (CTL) clones specific for trinitrophenyl (TNP)-modified spleen cells could develop an anomalous cytotoxicity against syngeneic and allogeneic tumor cells upon stimulation with TNP-modified spleen cells and high doses of human recombinant interleukin 2 (rIL-2). On FACS analysis, hyperactivated CTLs were positive for Thy-1, Ly 2 and LFA-1, but negative for L3T4 and asialo GM1. The staining profile of the cells with each antibody indicated that the CTL clones consisted of just one cell type. Monoclonal anti-Ly 2.2 and anti-LAA (lymphokine-activated cell-associated antigen) antibodies inhibited cytolysis of CTL and hyperactivated CTL clones against TNP-modified spleen cells, but failed to inhibit the anomalous killing of the hyperactivated CTL. The cold target competition test suggested the degeneracy of antigen specificity. The present study demonstrated that the CTL clone acquired a new specificity for tumor target cells upon stimulation with a high dose of rIL-2.

Novel immunosuppressive agent, FK506. In vitro effects on the cloned T cell activation

The present study shows the in vitro effects of a novel immunosuppressive agent, FK506, in comparison with cyclosporin A (CsA). FK506 inhibited concanavalin A response and allo-mixed lymphocyte reaction of murine splenic lymphocytes in a dose-dependent manner, and at 40- to 200-fold lower concentrations than CsA. Allo-cytolytic T lymphocyte induction from murine thymocytes was also inhibited by FK506, whereas the ability of cytolytic T lymphocyte to lyse targets was not affected by the agent. Immunosuppressive effects of FK506 were further characterized by using antigen specific-proliferative T lymphocyte clones, BC.21 and KO.6. FK506 inhibited the proliferation of T cell clones stimulated with specific antigens in a dose-dependent manner, and at about 100-fold lower concentrations than CsA. However, cloned T cells, once activated, were scarcely affected by the agent; interleukin-2 (IL-2) driven proliferation of cloned T cells was not inhibited. On the other hand, it was found that FK506 inhibited both IL-2 secretion and IL-2 receptor expression of BC.21 after stimulation with the specific antigen. FK506 also inhibited the proliferation of BC.21 stimulated with phorbol 12-myristate 13-acetate plus calcium ionophore, indicating that it directly affected the signaling pathway downward from the perturbation of the Ti/T3 complex. Finally, it was suggested that FK506 and CsA synergistically inhibited the antigen-driven proliferation of cloned T cells. These results indicate that the novel immunosuppressive agent, FK506, affects T cell activation with mechanisms similar to those of CsA but at considerably lower concentrations.

Novel immunosuppressive agent, FK506. In vitro effects on the cloned T cell activation

The present study shows the in vitro effects of a novel immunosuppressive agent, FK506, in comparison with cyclosporin A (CsA). FK506 inhibited concanavalin A response and allo-mixed lymphocyte reaction of murine splenic lymphocytes in a dose-dependent manner, and at 40- to 200-fold lower concentrations than CsA. Allo-cytolytic T lymphocyte induction from murine thymocytes was also inhibited by FK506, whereas the ability of cytolytic T lymphocyte to lyse targets was not affected by the agent. Immunosuppressive effects of FK506 were further characterized by using antigen specific-proliferative T lymphocyte clones, BC.21 and KO.6. FK506 inhibited the proliferation of T cell clones stimulated with specific antigens in a dose-dependent manner, and at about 100-fold lower concentrations than CsA. However, cloned T cells, once activated, were scarcely affected by the agent; interleukin-2 (IL-2) driven proliferation of cloned T cells was not inhibited. On the other hand, it was found that FK506 inhibited both IL-2 secretion and IL-2 receptor expression of BC.21 after stimulation with the specific antigen. FK506 also inhibited the proliferation of BC.21 stimulated with phorbol 12-myristate 13-acetate plus calcium ionophore, indicating that it directly affected the signaling pathway downward from the perturbation of the Ti/T3 complex. Finally, it was suggested that FK506 and CsA synergistically inhibited the antigen-driven proliferation of cloned T cells. These results indicate that the novel immunosuppressive agent, FK506, affects T cell activation with mechanisms similar to those of CsA but at considerably lower concentrations.