FK506 markedly enhances apoptosis of antigen-stimulated peripheral T cells by down-regulation of Bcl-xL.

BACKGROUND: FK506 is a clinically effective immunosuppressive agent and promoter of immunologic tolerance. However, limited information is available about the mechanism of FK506-induced immunosuppression. METHODS: In the present study, we investigated the molecular mechanism of FK506-mediated enhancement of apoptosis using in vivo activated T lymphocytes. We examined the effects of FK506 on apoptosis-related proteins in superantigen-stimulated peripheral T cells. Results. Injection of staphylococcal enterotoxin B (SEB) into BALB/c mice resulted in a selective apoptosis of splenic Vbeta8-positive T cells after 48 hr. Injection of FK506 within 36 hr of SEB injection resulted in a marked enhancement of DNA fragmentation of splenic Vbeta8+ T cells. FK506 did not affect the expression of Fas antigen on SEB-activated Vbeta8+ T cells. As Bcl-2-related proteins are involved in apoptotic process, we also evaluated their role by examining the expression of Bcl-2, Bcl-X(L), and Bax on SEB-FK506-treated murine splenic T cells. Although SEB injection slightly increased the expressions of Bcl-2 and Bax on V138+ T cells, FK506 did not modulate Bcl-2 or Bax expression in these cells. In contrast, the expression of Bcl-x(L) on Vgamma8+ T cells, which was markedly induced by SEB, was abrogated by FK506. Conclusions. Our findings indicate FK506-induced enhancement of apoptosis of activated T cells is mediated by down-regulation of Bcl-X(L) expression on these cells. Our results also suggest that Bcl-x(L) is a critical determinant of apoptosis of activated T cell and may represent a potential target for new therapies designed to achieve immunological tolerance.     

Effect of FK506 on donor T-cell functions that are responsible for graft-versus-host disease and graft-versus-leukemia effect

BACKGROUND: FK506 is a potent immunosuppressive agent that is used in human graft-versus-host disease (GvHD) prevention. However, the precise mechanisms for GvHD prevention and the effect on graft-versus-leukemia (GvL) activity are unknown. This study was undertaken to determine the effect of FK506, given at clinically relevant doses, on donor T-cell functions responsible for GvHD and GvL activity. METHODS: The effect of FK506 on GvHD prevention and GvL activity was investigated using a murine model of allogeneic bone-marrow transplantation in which mice were injected with a P815 leukemic cell line. The regulatory role of FK506 on donor T cells was tested by analysis of donor T-cell expansions in the spleen and donor anti-host T-cell proliferative and cytotoxic responses. mRNA expression of type 1 T helper (Th1), Fas ligand (L), and granzyme B were also evaluated in target organs of GvHD. RESULTS: FK506 significantly prolonged the survival of GvHD mice when given at the trough level of 17.6 ng/mL, whereas it also blocked GvL effect in P815-injected GvHD mice. FK506 reduced the expansion of donor CD8+ and, to a lesser extent, CD4+ T cells in the spleen and inhibited donor anti-host T-cell proliferative and cytotoxic responses. It also inhibited the induction of Th1, FasL, and granzyme B mRNA expression in target organs of GvHD. CONCLUSIONS: FK506 inhibits both GvHD and GvL activity when given at clinical doses by inhibiting donor T-cell expansion, donor anti-host T-cell reactivity, and Th1 immune responses.     

Effect of a new immunosuppressive agent, FK506, on human lymphocyte responses in vitro. I. Inhibition of expression of alloantigen-activated suppressor cells, as well as induction of alloreactivity

The effect of FK506 on in vitro human lymphocyte responses was assessed in comparison with cyclosporine. FK506 suppressed, in a dose-dependent fashion, the lymphocyte response to stimulation with PHA and with alloantigens in primary mixed lymphocyte reactions at a 70-100-fold lower concentration than CsA--namely, 50% inhibition (IC50) was obtained with 8.6 nM FK506 and with 750 nM CsA in the PHA response, and with 0.21 nM FK506 and with 20 nM CsA in MLR. Allocytolytic T lymphocyte induction was also inhibited by FK506, whereas the ability of CTL to lyse targets was not affected by the agent, indicating that FK506 did not affect the recognition and binding of alloantigen by CTL. FK506 inhibited, in a dose-dependent fashion, both IL-2 receptor and transferrin receptor expression on the alloactivated lymphocytes--whereas this agent inhibited only incompletely both expression of both receptors on lymphocytes stimulated with PHA. Lymphocytes from primary MLR cultured in the presence of FK506 were tested for suppressor cell activity on day 8 of culture. FK506 did not allow for the expression of alloantigen-activated suppressor cells when used in a dose sufficient to inhibit CTL generation.     

The immunosuppressive action of FK506. In vitro induction of allogeneic unresponsiveness in human CTL precursors.

FK506 is an unusually potent new immunosuppressive agent that inhibits T cell-mediated immunity in vivo and in vitro. In these studies we sought to further elucidate the immunosuppressive mechanism of action of FK506 on human allogeneic MLR-induced CTL activation. FK506 induced suppression of cell-mediated lympholysis by PBMC was optimal at 1-2-nM concentrations, if added at the initiation of 6 day CML cultures. The sensitivity to suppression decreased with time, and fully differentiated effectors were resistant to inhibition by FK506. Suppression of CML was not reversed by washing the cultures, adding exogenous IL-2, or restimulating with fresh cells. Pretreatment of unfractionated or adherent allogeneic PBMC with FK506 blocked the stimulating activity of these cells. Furthermore, addition of FK506-treated stimulator cells to cocultures containing untreated responder and stimulator cells resulted in suppression of CML. The inhibition in the cocultures was greatest if the FK506-pretreated cells were autologous to the original stimulator, suggesting a relative specificity in the suppression obtained under these conditions. These studies suggest that, in addition to suppressing the response of alloreactive CTL precursors, FK506 reduces the ability of irradiated allogeneic PBMC to induce CTL generation.     

他克莫司对肝移植受者外周血T淋巴细胞亚群及共刺激分子表达的影响

目的 探讨他克莫司（FK506）对肝移植受者外周血T淋巴细胞亚群及其表面共刺激分子表达的影响。方法 采用荧光标记单克隆抗体和流式细胞技术，测定术后采用FK506治疗的肝移植受者（FK506治疗组）在用FK506后1、2、3、4周时的外周血T淋巴细胞亚群及其表面共刺激分子CD28、CD152和ICOS分子的表达情况，以健康志愿者（健康对照组）和患终末期肝脏疾病拟行肝移植者（肝病对照组）为对照。结果 CD3^＋T淋巴细胞在各组间的差异均无统计学意义（P〉0．05）。经FK506治疗后，肝移植患者的CD4^＋T淋巴细胞逐渐减少，CD8^＋T淋巴细胞逐渐增加，并恢复至健康对照组水平（P〉0．05）。FK506治疗组T淋巴细胞亚群表面CD28分子和ICOS分子表达逐渐下降，并明显低于健康对照组（P〈0．05），而CD152分子表达增加，且明显高于健康对照组（P〈0．05）；其ICOS分子表达水平的下降晚于CD28分子，CD4^＋CD28^＋T淋巴细胞、CD8^＋CD28^＋T淋巴细胞和CD4^＋ICOS^＋T淋巴细胞均呈现相近的变化规律。结论 FK506能迅速纠正移植受者T淋巴细胞亚群紊乱，并抑制正性共刺激分子CD28和ICOS的表达，促进负性共刺激分子CD152的表达。     

Experimental studies on the mode of action of cyclosporine and FK506 assessed by proliferation response of human cloned T lymphocytes]

We applied cloned human T lymphocytes established in our laboratory to evaluate the mode of action of Cyclosporine (CsA) and FK506. Phenotypic and functional analysis led us to conclude that HTL403 was a helper T cell clone and HTL805 a cytotoxic one. Susceptibility of HTL-403 to the immunosuppressants demonstrated that alloantigen-driven proliferative response can recover to the rIL2-driven level by the addition of rIL2 at higher concentration of the agents. Although full recovery was not observed in FK506, this finding indicated that FK506 as well as CsA inhibit IL2 secretion from HTL403. FK506 showed remarkable suppressive effect on the proliferative response of HTL-805 even at a considerably low concentration, while CsA suppressed such a response dose-dependently. We concluded that FK506 can be used to reverse ongoing acute rejection as well as to prevent acute rejection.     

环孢素A及FK506对人肝癌细胞株增殖的影响

目的:探讨免疫抑制剂环孢素(CsA)及他克莫司(FK506)对肝癌细胞增殖的影响及可能机制。方法:采用噻唑蓝(MTT)比色法观察CsA及FK506对QGY鄄7701、QGY鄄7703、SMMC鄄7721和BEL鄄7402等4株肝癌细胞增殖的影响。还应用Hoechst33258荧光染料涂片,在荧光显微镜下观察用药组细胞的形态学改变。结果:随着作用时间延长,10μM的CsA对4株肝癌细胞均呈现明显的生长抑制效应(P<0.01),而0.5μM的FK506与对照组相比,其生长抑制作用不明显(P>0.05)。荧光显微镜下CsA用药组肝癌细胞呈现凋亡改变;而FK506用药组与对照组无显著差异。结论:免疫抑制剂CsA非但未促进体外肝癌细胞生长,相反呈明显的抑制效应。FK506尽管未呈现对肝癌细胞增殖的抑制效应,也未显示有生长促进作用。CsA对肝癌细胞的增殖抑制作用与诱导癌细胞发生凋亡有关。     

FKBP12 is the only FK506 binding protein mediating T-cell inhibition by the immunosuppressant FK506

BACKGROUND: FK506-binding proteins (FKBP) are immunophilins that interact with the immunosuppressive drugs FK506 and rapamycin. Several FKBP family members such as FKBP12, FKBP12.6, and FKBP51 are expressed in T cells. It has been speculated that these FKBPs are possibly redundant in the immunosuppressant-induced T-cell inactivation. To determine the pharmacological relevance of multiple FKBP members in the immunosuppressant-induced T-cell inactivation, we have investigated the physiological responses of FKBP12-deficient and FKBP12.6-deficient mutant T cells to the immunosuppressive agent FK506. METHODS: FKBP12-deficient and FKBP12.6-deficient T cells were isolated from genetically engineered FKBP12-deficient and FKBP12.6-deficient mice, respectively. T-cell growth inhibitory assay was used to assess their responses to immunosuppressant FK506 treatments. RESULTS: We found that growth inhibition induced by FK506 is abolished in FKBP12-deficient cells but not in FKBP12.6-deficient cells. CONCLUSIONS: FKBP12 is the only FKBP family member that plays a key role in immunosuppressant-mediated immunosuppression.     

T细胞疫苗联合FK506抑制异种神经移植排斥的实验研究

目的 研究T细胞疫苗接种联合应用FK506对大鼠异种神经移植排斥反应的抑制作用. 方法 利用BABL/c小鼠的脾细胞免疫SD大鼠,取后者脾细胞活化所制备的T细胞疫苗对异种神经移植受体的SD大鼠进行免疫,移植后联合应用FK506.以异种神经移植后混合淋巴细胞培养、微量细胞毒测定、移植神经的组织学观察和胫前肌湿重测定等,对该方法抗大鼠异种神经移植排斥反应的作用加以分析. 结果 和对照组相比较,T细胞疫苗接种联合FK506使神经移植大鼠胫前肌湿重明显增加(P＜0.05),淋巴细胞转化率等排斥反应指标差异也具有统计学意义(P＜0.05). 结论 T细胞疫苗接种联合应用FK506能显著抑制大鼠异种神经移植的免疫排斥反应.     

FK506免疫抑制机理的研究

通过采用淋巴细胞增殖试验，混合淋巴细胞反庆和间接免疫荧光法分析淋巴细胞表面白细胞介素２受体（ＩＬ－２Ｒ）和ＴｆＲ的表达，研究了ＦＫ５０６的免疫抑制作用。结果表明，ＦＫ５０６对植物血凝素（ＰＨＡ）诱导的淋巴细胞增殖具有强烈的抑制作用，５０％抑制浓度＊ＩＣ５０）为１．３５ｎｍｏｌ／Ｌ，外源性ＩＬ－２不能逆转这种作用；对混合淋巴细胞反应（ＭＬＲ）有显著抑制作用，其ＩＣ５０为０．１２ｎｍｏｌ／Ｌ；在由ＰＨ     

Requirement for help in the generation of alloantigen-specific helper cells

Control mechanisms that regulate the induction of T helper cells are a key component of conceptual schemes to understand the network of interactions controlling the immune response. In this work, using a sequential three-step culture system, we demonstrate that the generation of the T helper cells that participate in cytotoxic T cell induction is itself dependent on interactions with helper cells. The induction of Ly7- pre-Th requires collaboration with a Th-directed Ly1+7+ helper T cell with radioresistant function and the participation of an adherent cell. Th have been generated from thymic responders and from anti-Ly7-treated splenic responders, both of which are deficient in Th effector function. Approximately 10-30-fold more help is generated from splenic as compared with thymic pre-Th. Ly7+ Th were required throughout the first 5 days of CTL generation. Using a limiting dilution analysis of pre-Th we have shown that splenic precursor Th are inducible with IL-2, but that the frequency of clones able to deliver antigen-specific help in a CTL response is an order of magnitude lower than the frequency of clones induced by antigen and able to secrete IL-2 reported by others. For reasons described in the discussion, we suggest that Th and IL-2 secretors may be at least partially nonoverlapping subsets. The CTL-directed Th effectors induced by IL-2 were analyzed for specificity; 65% of clones were challenge-specific, 29% were crossreactive, and 6% were heteroclitic. We conclude that the Th that participate in the induction of pre-Th coexist with, and bear markers similar to, the Th that act in the induction of pre-T suppressor cells, and of CTL. It seems possible that the control over the class of precursor induced by antigen may be a function of the quantity rather than the quality of helper effectors.     

Low-Dose FK506 Blocks Collar-Induced Atherosclerotic Plaque Development and Stabilizes Plaques in ApoE−/− Mice

Since atherosclerosis is a chronic inflammatory disease, we tested the hypothesis that the immunosuppressive drug FK506 would attenuate the development of atherosclerosis using a mouse model of collar-induced atherosclerosis. ApoE-/- mice were treated for 4 weeks with the immunosuppressive drug FK506 (0.05 mg/kg/day), yielding sustained blood levels (approximately 0.2 ng/mL) without systemic side effects. Atherosclerotic plaque development of FK506-treated mice was significantly reduced (63%) while plaque cell density was increased (52%) compared to controls. Importantly, FK506 also blocked progression of pre-existing atherosclerotic plaques. Plaque area of pre-existing plaques was 35% reduced by FK506. Cell density (35%) and collagen content (51%) were significantly increased, whereas necrotic core content was decreased (42%), indicating a more stable plaque morphology. Similar results were found during spontaneous atherosclerotic plaque development in ApoE-/- mice (treatment 17-25 weeks of age). Flow-cytometric analysis showed no peripheral effects on blood cell count or T-cell activation after FK506-treatment. In vitro, FK506 decreased vascular smooth muscle cell (VSMC) apoptosis and inhibited nuclear factor of activated T cells (NFAT)-luciferase reporter activity at concentrations in the range of the in vivo concentration. Low-dose FK506 inhibits collar-induced atherosclerotic plaque development and progression and induces more stable plaque phenotypes in ApoE-/- mice without any peripheral side effects.     

Regulatory effect of FK506 on CD152 and PD-1 in the liver allorecipients

AIM: We dynamically observed the expression of CD152 and PD-1 on T-cell surfaces in peripheral blood of liver allorecipients to explore the regulatory effect of FK506 on negative costimulatory molecules. METHODS: We evaluated 20 liver allorecipients, 19 end-stage liver disease patients, and 20 healthy volunteers for FK506 concentrations measured by an enzyme-multiplied immunoassay technique and flow cytometry to determine T-cell subsets as well as CD152 and PD-1 expression. RESULTS: After liver transplantation, the frequency of CD4+ T cells gradually decreased to significantly lower level than those in the disease controls (P < .05). CD8+ T cells in each treatment group were obviously higher than those in the disease controls (P < .05). The expression of CD152 on CD4+ and CD8+ T cells was greater than those in healthy controls (P < .05); and at 2 and 4 weeks, higher than those in disease controls (P < .05). The expression of PD-1 on CD4+ T cells from the 2 weeks after treatment was significantly greater than that in healthy controls (P < .05), and that on CD8+ T cells increased obviously from the 4 weeks compared with disease controls (P < .05). CONCLUSION: FK506 up-regulated the expression of CD152 and PD-1 on the T-cell surface inhibiting proliferation and activation of effector T cells, favoring the survival of allorecipients.     

FK506 (tacrolimus) increases halothane-induced Ca2+ release from skeletal muscle sarcoplasmic reticulum

BACKGROUND: FK506 binding protein is closely associated with the sarcoplasmic reticulum ryanodine receptor-channel and can modulate its function. The ryanodine receptor is stabilized by its association with FK506 binding protein. The immunosuppressant drugs FK506 (tacrolimus) and rapamycin can promote dissociation of FK506 binding protein from the ryanodine receptor 1 and by this mechanism increase sensitivity of ryanodine receptor 1 to agonists such as caffeine. Furthermore, it was shown recently that treatment of normal human skeletal muscle with FK506 and rapamycin increased halothane-induced contracture. The authors investigated the effect of the immunosuppressants FK506 and rapamycin on halothane-induced Ca2+ release in skeletal muscle sarcoplasmic reticulum vesicles. METHODS: Skeletal muscle terminal cisterns were isolated from New Zealand White rabbits. Ca2+ uptake and release was monitored in skeletal muscle sarcoplasmic reticulum vesicles using the fluo-3 fluorescent technique. Western Blot analysis of FK506 binding protein was performed using standard protocol. RESULTS: The authors observed that treatment of skeletal muscle sarcoplasmic reticulum vesicles with FK506 and rapamycin enhances halothane-induced Ca2+ release by about five times. Furthermore, the Ca2+ release induced by halothane in the presence of FK506 was inhibited by several antagonists of the ryanodine receptor, such as ruthenium red, spermine, and Mg2+. CONCLUSION: Dissociation of FK506 binding protein from its binding site in skeletal muscle sarcoplasmic reticulum vesicles can modulate halothane-induced Ca2+ release through the ryanodine receptor. Data are discussed in relation to the role of the FK506 binding protein in modulating the effect of halothane on the ryanodine receptor and the development of malignant hyperthermia phenotype.     

Human T cell responses to human and porcine endothelial cells are highly sensitive to cyclosporin A and FK506 in vitro

BACKGROUND: Human T cells proliferate in response to both human umbilical vein endothelial cells (HUVEC) and porcine aortic endothelial cells (PAEC) via the second signals LFA-3/CD2 and B7-2 (CD86), respectively. Previous studies have shown that stimulation of T cells via CD28 or phorbol myristate acetate (PMA) activation is highly resistant to inhibition by cyclosporine A (CsA) and tacrolimus (FK506), as is the response of T cells to phytohemmaglutinin in the presence of endothelial cells. We have investigated the inhibitory effects of CsA and FK506 on the direct response of human CD4+ T cells to HUVEC and PAEC and the effect of adding B7-1 transfectants. METHODS: T cell proliferation, interleukin-2 release bioassays and a multiple cytokine bioassay employing the TF-1 cell line were used as indicators of T cell responses to HUVEC and PAEC either in the presence or absence of CsA and FK506. In some experiments, B7-1 transfectants were also added. RESULTS: Proliferative responses and interleukin-2 release were highly sensitive to CsA, the ID50 being significantly less for HUVEC (6.5 ng/ml) than PAEC (15 ng/ml). The ID50 of CsA for the mixed lymphocyte response (MLR) was similar to PAEC (18.6 ng/ml), all these values being significantly less than the T cell activation by phytohemmaglutinin (PHA) (227 ng/ml). Addition of B7-1 transfectants significantly increased interleukin-2 production by T cells/HUVEC and resistance to CsA was greatly increased to an ID50 of > 1000 ng/ml. In contrast, addition of B7-1 transfectants to T cells/PAEC had no effect either on T cell proliferation, IL-2 production, or CsA resistance. Similar results were obtained with FK506. Using the TF-1 cell line, it was determined that cytokines other than IL-2 are released during CD4+ T cell/EC interactions, with similar sensitivity to CsA and FK506. CONCLUSIONS: It is concluded that both allogeneic and xenogeneic T cell/endothelial responses should be inhibited by therapeutic levels of CsA in vivo, assuming the absence of trans-stimulation by B7 molecules.     

FK 506 inhibits tolerance induction in mice liver transplantation

BACKGROUND: In the orthotopic mouse liver transplantation model, allografts are accepted without immunosuppression, and donor-specific tolerance is induced upto 40 days. Although FK 506 is a well-known immunosuppressive agent, its influence on tolerance induction is not known. In this study, we examined the influence of FK 506 on tolerance induction in a mouse liver transplant model. METHODS: Orthotopic liver transplantation was performed from B10.BR (H-2K) to B10.D2 (H-2D mice). In the experimental group, FK 506 (1 mg/kg/d) was given subcutaneously to the recipients from day 0 to day 21, whereas the control group received a placebo (1 mg/kg/d). On day 40, donor skin grafts were transplanted to the recipients to examine the survival times of the recipients and the skin grafts. On day 14, donor-type cells in recipient's blood, spleen, kidney, thymus, and lymph nodes were examined by RT-PCR using specific donor-type MHC class I and II primers. RESULTS: All recipients survived for more than 100 days. The mean survival time of skin grafts in the experimental group was significantly reduced compared to that of controls. On day 14, either donor-type MHC class I- or class II-positive cells were detected in the control group, whereas donor-derived MHC class II-positive cells disappeared in the experimental group. CONCLUSIONS: In the early period after mouse liver transplantation, FK 506 inhibits tolerance induction paradoxically. Some donor-derived MHC class II-positive cells might play an important role in tolerance induction.     

Effects of intrathecal administration of FK506 after sciatic nerve crush injury

Although various administration routes of FK506 have been published, intrathecal administration of FK506 has not previously been reported in the literature. A daily dose of 0.05 mg/kg of FK506 was given (a small dose compared with those reported in the available literature). The authors used this small dose to obtain lower immunosuppression and neurotoxicity, and a higher axonal regeneration rate. A total number of 40 female Wistar rats were used and randomly divided into four groups: control, sham, FK506-treated, and vehicle-treated. Sciatic nerve regeneration was evaluated by walking track analysis, an electrostimulation test, and light microscopic evaluation. There was a statistically significant difference ( P < 0.05) between FK506-treated and vehicle-treated groups at the end of 6 weeks according to both the walking track analysis and the electrostimulation test. Comparing the stimulus thresholds of the sham and FK506-treated group, no significant difference ( P > 0.05) was observed. Evaluation of the data revealed that FK506 had a beneficial effect on sciatic nerve regeneration.     

转化生长因子-β1在他克莫司肾毒性中的作用

目的 观察转化生长因子(TGF)-β1在他克莫司大鼠肾毒性中的作用.方法 将SD大鼠24只随机分成对照组、CsA组、FK506组和FK506+Dil组,用药4周后建立起各组大鼠模型.观察各组大鼠的肾功能,应用免疫组织化学技术检测各组大鼠TGF-β1的表达.结果 FK506组大鼠的血肌酐值为(34.17±4.54)μmol/L,肌酐清除率为(0.58±0.39)ml·min-1·100g-1,与对照组比较差异有统计学意义(P<0.05).FK506组TGF-β1的阳性表达率均为100%(6/6),对照组TGF-β1的阳性表达率为16%(1/6),两者差异有统计学意义(P<0.05). 结论 TGF-β1可能介导了FK506引起的肾毒性.     

Lesser reduction in bone mineral density by the immunosuppressant, FK506, compared with cyclosporine in rats

BACKGROUND: Posttransplantation osteopenia leading to osteoporosis induced commonly by treatment with immunosuppressants including cyclosporine (CsA) is a severe complication and results in lowering the quality of life in patients receiving organ transplantation. FK506 is a newly developed immunosuppressant and is currently being used for the prevention of rejection after organ transplantation. In this study, to investigate whether FK506 as well as CsA would cause osteopenia or not, we evaluated the effect of FK506 on bone mineral density and several parameters relevant to bone metabolism in comparison with that of CsA using normal rats. METHODS: Ten-week-old male Sprague-Dawley rats were treated with FK506 (vehicle, 1 mg/kg, and 3.2 mg/kg) or CsA (vehicle, 10 mg/kg, and 32 mg/kg) by daily oral gavage for 28 days. Bone mineral density of the femur, plasma insulin-like growth factor I (IGF-I), and urinary deoxypyridinoline were determined by peripheral quantitative computerized tomography, radioimmunoassay, and enzyme-linked immunosorbent assay, respectively. RESULTS: The reduction in bone mineral density of the femur was observed in both FK506- and CsA-treated rats. The reduction in CsA-treated rats, however, was statistically significant and strikingly severe, whereas that in FK506-treated rats was much less severe than CsA. Plasma IGF-I levels were significantly elevated in FK506-treated rats but not in CsAtreated rats. Urinary deoxypyridinoline levels were unchanged in FK506-treated rats but elevated in CsA-treated rats. CONCLUSIONS: Compared with CsA, FK506 does not appear to induce severe osteopenia by high-turnover bone metabolism in the rat by mediating via IGF-I induction in part. The results suggest that FK506 may exert favorable effects on bone metabolism in patients with organ transplantation compared with CsA. To assess this idea, further clinical investigations focused on bone metabolism will be required.