Composite tissue allotransplantation in newborns: a swine model.

BACKGROUND: Management of congenital limb aplasia or facial malformations could be improved by composite tissue allotransplantation (CTA), a technique that has never been performed in newborns. For this, however, the induction of donor-specific tolerance would be mandatory, as long-term immunosuppression is not acceptable in this non-lifesaving procedure. Induction of tolerance has been shown to be possible in a newborn CTA rat model but has never been tested in large-animal models. Our goals were to establish a model of CTA in newborn swine to see if tolerance could be obtained without immunosuppression and to assess rejection or tolerance properties via clinical and histologic examinations. MATERIALS AND METHODS: We applied a CTA heterotopic knee swine model. We performed two series of surgical procedures: Series 1 was 20 autografts in 6-day-old (1-10) 2,544 kg (1,140-4,060 kg) piglets; Series 2 was 10 allografts without immunosuppression between outbred animals aged 7.8 d (6-10) and weighing 2,770 kg (2,200-3,550 kg). RESULTS: In Series 1, six early deaths and two cases of vascular failure were observed. In Series 2, no spontaneous deaths were observed and all piglets presented clinical and histologic rejection. CONCLUSIONS: Our findings strongly suggest that newborn immunologic status is not sufficient for the development of tolerance in large animals without immunologic intervention. Complications and animal death after transplantation correlate with age and weight. Low rates for both vascular failure and postoperative death permit the use of this model in piglets weighing over 2 kg and aged more than 6 d for research on newborn CTA.

Cellular basis of tissue regeneration by omentum.

The omentum is a sheet-like tissue attached to the greater curvature of the stomach and contains secondary lymphoid organs called milky spots. The omentum has been used for its healing potential for over 100 years by transposing the omental pedicle to injured organs (omental transposition), but the mechanism by which omentum helps the healing process of damaged tissues is not well understood. Omental transposition promotes expansion of pancreatic islets, hepatocytes, embryonic kidney, and neurons. Omental cells (OCs) can be activated by foreign bodies in vivo. Once activated, they become a rich source for growth factors and express pluripotent stem cell markers. Moreover, OCs become engrafted in injured tissues suggesting that they might function as stem cells.Omentum consists of a variety of phenotypically and functionally distinctive cells. To understand the mechanism of tissue repair support by the omentum in more detail, we analyzed the cell subsets derived from the omentum on immune and inflammatory responses. Our data demonstrate that the omentum contains at least two groups of cells that support tissue repair, immunomodulatory myeloid derived suppressor cells and omnipotent stem cells that are indistinguishable from mesenchymal stem cells. Based on these data, we propose that the omentum is a designated organ for tissue repair and healing in response to foreign invasion and tissue damage.

¿Existe correlación entre el peso y la talla del paciente con el largo y diámetro del injerto semitendinoso? / Does patient weight and height correlate with the length and diameter of the semitendinosus graft?

Objetivo. Describir correlación entre largo y ancho del tendón semitendinoso (ST) con peso, talla y edad en la población hispana. Método. Estudio prospectivo de una serie consecutiva de 61 pacientes sometidos a reconstrucción del ligamento cruzado anterior (LCA) con tendones semitendinoso y gracilis; 40 varones (67,2%) y 21 mujeres (32,8%). La edad media fue de 28,3±10,2 años (17-55). En pabellón se midieron el largo del ST y el diámetro del ST cuádruple (ST4). Se correlacionaron los hallazgos con peso, talla y edad, agrupando y separando por género, y se documentaron las diferencias entre variables. Resultados. El diámetro medio del ST4 fue de 9,0±1,3mm, siendo en pacientes masculinos de 9,3±0,8mm y en pacientes de sexo femenino de 8,3±0,6mm (p<0,05). La longitud media del ST fue de 28,1±3,4cm, siendo en pacientes masculinos de 28,5±2,3cm y en pacientes de sexo femenino de 26,0±2,5cm (p<0,05). El peso se correlacionó positivamente con el largo ST (0,47, p<0,001) y el diámetro ST4 (0,51, p<0,001). Asimismo la talla del paciente se correlacionó positivamente con el largo ST (0,57, p<0,001) y diámetro ST4 (0,34, p=0,008). No se encontró correlación significativa entre la edad de los pacientes y las medidas del tendón estudiadas. Conclusión. En el grupo general de pacientes estudiado existía una correlación positiva entre la longitud del ST con talla y peso del paciente. Asimismo, se objetivaba una correlación positiva entre el diámetro del ST4 con talla y peso del paciente(AU)

Objective. To describe the correlation between the length and diameter of semitendinosus tendon (ST), and weight, height and age in Hispanic population. Methods. Prospective study of a consecutive series of 61 patients that underwent anterior cruciate ligament (ACL) reconstruction with hamstrings; 40 (67.2%) males and 21 (32.8%) females. The average age was 28.3±10.2 years (range 17-55). In the operating room, length and diameter of ST folded in four bundles (ST4) were measured. Correlations were calculated using patient weight, height and age, including males and females and separating them by gender. Results. Mean ST4 diameter: 9.0±1,3mm. Males ST4 diameter: 9.3±0.8mm; females ST4 diameter 8.3±0.6mm (p<0.05). Average ST length: 28.1±3.4cm. Males mean length 28.5±2.3cm; females mean length 26.0±2.5cm (p<0.05). Weight was correlated directly with ST length (c=0.47; p<0.001) and ST4 diameter (c=0.51; p<0.001). Patient height was directly correlated with ST length (c=0.57; p<0.001) and ST4 diameter (c=0.34; p=0.008). There was no correlation between patient age and tendon measurements. Conclusion. A positive correlation was found between ST length and patient weight and height for the general population. A direct correlation was also observed between ST4 diameter and patient weight and height for the general population (AU)

Comparison of arterial stiffness and microcirculatory changes following abdominal aortic aneurysm grafting.

BACKGROUND: Abdominal aortic aneurysm (AAA) surgery provides a unique opportunity to study the impact of arterial stiffness on central haemodynamics, reflected in augmentation index (AI). The aneurysmal aorta is significantly stiffer than undilated age-matched aorta. AIM: We investigated whether replacement of an aneurysmal aorta with a compliant graft would result in a decrease in AI, which would thus decrease myocardial workload parameters. METHODS: Patients undergoing elective open or endovascular AAA repair were assessed with applanation tonometry and laser fluximetry pre-operatively, immediately and long-term post-operatively. RESULTS: Replacement of a small segment of abnormal conduit vessel resulted in improvements in AI, demonstrating that arterial stiffness can be surgically manipulated. CONCLUSIONS: These results reflect a decreased myocardial workload post-aortic grafting. This decrease in AI is important from a risk factor management perspective, and arterial stiffness should become a further recognised and screened for risk factor in patients with known aneurysmal disease.

Methods of assessment of cortical plasticity in patients following amputation, replantation, and composite tissue allograft transplantation.

The brain is always adapting to new inputs from the environment. New noninvasive techniques are available to scrupulously study cortical plasticity. Several studies have proven that these modifications of neural pathways occur because of denervation from injury such as amputation. Changes that occur rapidly are likely because of unmasking of established synapses that are latent, whereas changes that occur over long periods of time are more likely because of establishment of new neural connections. Cortical reorganization that occurs from traumatic amputation has been shown to be reversible with replantation and transplantation. With the new field of composite tissue transplantation, such as hand or face, it is critical to be aware of these changes to choose potential patients and to modify their rehabilitation, on the basis of our understanding of the cortical reorganization that occurs over time.

Transplantation or removal of intra-abdominal adipose tissue prevents age-induced glucose insensitivity.

Increases in intra-abdominal fat, a common feature associated with aging, is an established risk factor for insulin resistance, diabetes and the metabolic syndrome. To examine the direct contribution of intra-abdominal fat in the pathophysiology of insulin resistance we altered fat volume via removal or transplantation in a naturally occurring age-induced moderate model of obesity and insulin resistance. This was accomplished by bilateral removal of epididymal white adipose tissue (Lipx) or transplantation of donor fat into the intra-abdominal side of the peritoneal cavity of 28-week old rats. Control animals received sham surgery. Glucose tolerance was evaluated at baseline and 4 and 8weeks post-surgery in all groups, and fasting insulin and leptin were additionally measured in 28-week old rats. In addition, fasted and fed triglyceride, cholesterol and fatty acid concentrations were measured. Before surgery 28-week old rats weighed more and were glucose intolerant compared with 8-week old controls. Both Lipx and transplantation significantly prevented age-induced decreases in glucose tolerance, with Lipx causing improvement at 4weeks which declined by 8weeks; and with a significant transplantation improvement at 8weeks only. Lipx significantly increased insulin secretion 15min after a bolus injection of 0.75mg/kg dextrose at 4 and 8weeks compared with controls, while transplantation caused a significant ( approximately 220%) increase in fasted leptin level at 4weeks only. Taken together, these data suggest that surgical removal or addition of intra-abdominal fat prevents age-induced insulin resistance by different mechanisms and is a suitable model to investigate naturally occurring obesity.

Schwann cell migration is integrin-dependent and inhibited by astrocyte-produced aggrecan.

Schwann cells transplantation has considerable promise in spinal cord trauma to bridge the site of injury and for remyelination in demyelinating conditions. They support axonal regeneration and sprouting by secreting growth factors and providing a permissive surface and matrix molecules while shielding axons from the inhibitory environment of the central nervous system. However, following transplantation Schwann cells show limited migratory ability and they are unable to intermingle with the host astrocytes. This in turn leads to formation of a sharp boundary and an abrupt transition between the Schwann cell graft and the host tissue astrocytes, therefore preventing regenerating axons from exiting the graft. The objective of this study was to identify inhibitory elements on astrocytes involved in restricting Schwann cell migration. Using in vitro assays of cell migration, we show that aggrecan produced by astrocytes is involved in the inhibition of Schwann cell motility on astrocytic monolayers. Knockdown of this proteoglycan in astrocytes using RNAi or digestion of glycosaminglycan chains on aggrecan improves Schwann cell migration. We further show aggrecan mediates its effect by disruption of integrin function in Schwann cells, and that the inhibitory effects of aggrecan can overcome by activation of Schwann cell integrins.

Spontaneous pigmentation of non-pigmented palatal tissue after periodontal surgery.

BACKGROUND: A 22-year-old African American female was referred for augmentation of keratinized gingiva around implants at the right and left maxillary second premolar sites. Presurgical evaluation revealed generalized melanosis of the buccal gingiva and a lack of keratinized tissue around implants at sites #4 and #13. No pigmentation was noted on the palatal tissues. METHODS: Thick free gingival grafts were harvested bilaterally from the non-pigmented palate and secured to the recipient sites with bioabsorbable sutures. Hemostasis was achieved at the palatal donor sites with moistened gauze, and an acrylic stent was delivered for patient comfort. RESULTS: Both palatal donor sites healed with spontaneous pigmentation. The pigmentation intensified with time but resulted in no adverse outcome. CONCLUSIONS: Post-surgical healing in patients with gingival pigmentation is not entirely predictable, as multiple studies have demonstrated widely inconsistent results in regards to gingival pigmentation upon healing. When performing periodontal plastic surgery in patients with pigmented oral tissues, it is important to discuss all possible outcomes, including spontaneous pigmentation.

Mild rejection episode evoked by modification of immunosuppressive protocol observed in a patient with forearm transplantation: case report.

Skin is the most immunogenic component of a composite tissue allograft (CTA). Clinicopathologic monitoring of the skin seems to be the most reliable method to detect rejection in CTA patients. The symptoms in cases demonstrating full-blown rejection are clear, contrary to those of just mild rejection. The aim of the study was to present the symptoms of mild rejection observed in a midforearm transplant patient at 20 months postoperative. The 32-year-old man underwent right dominant forearm transplantation at 12 years after a traumatic amputation. During the first 20 months, the course was uneventful, with no signs of impaired function. Immunotherapy at 20 months consisted of: Cellcept (2 g/d), prednisolone (10 mg/d), tacrolimus (7 mg/d; level C(0) of 13 ng/mL), An attempt was made to modify therapy by diminishing the tacrolimus dose to 4 mg/d (C(0)-8 ng/mL). After 10 days postimplementation of the new regimen, are hardly visible macullopapular erythematous rash appeared on the palmar and dorsal sides of the hand as well as the skin of the forearm. There was a slight red swelling of the nail bed margins. No deterioration of hand function was observed. The patient was immediately admitted to the hospital; despite unclear clinical and pathomorphological symptoms, we diagnosed a mild rejection (grade I). The therapy consisted of methylprednisolone (500 mg three times daily for 3 consecutive days) and 5 days of topical application of immunosuppressant ointments (tacrolimus and Protopic) with maintenance of the previously applied oral tacrolimus doses. After 5 days of treatment, the symptoms subsided. This approach utilized the advantage of the unique possibility to treat rejection locally, consistent with current awareness that skin is the primary target of hand rejection. However, topical application of immunosuppressants has not been extensively investigated. The manifestations of rejection in CTA patients may be heterogeneous and difficult to diagnose.

Prolongation of composite tissue allograft survival by immature recipient dendritic cells pulsed with donor antigen and transient low-dose immunosuppression.

BACKGROUND: Composite tissue allograft transplantation is limited by risks of long-term immunosuppression. The authors investigated whether short-term immunosuppression combined with recipient immature dendritic cells pulsed with donor antigens promotes composite tissue allograft survival. METHODS: Orthotopic hind-limb transplants were performed (day 0) from Wistar-Furth (RT1) to Lewis (RT1(u)) rats. Recipient dendritic cells were propagated from bone marrow with granulocyte-macrophage colony-stimulating factor (bone marrow-derived dendritic cells) and pulsed with or without donor splenic cell lysate. Recipients were as follows: group I, control; group II, cyclosporine (10 mg/kg/day, days 0 through 6, intraperitoneally); group III, antilymphocyte serum plus cyclosporine (days -4 and +1, intraperitoneally); and groups IV and V, cyclosporine plus antilymphocyte serum, combined with 7 x 10(6) untreated or donor cell lysate-pulsed bone marrow-derived dendritic cells (days +7 and +14, intravenously), respectively. Epidermolysis/desquamation of donor skin defined rejection. Mixed leukocyte reaction determined recipient T-cell reactivity to donor. Tissue samples were obtained at 3 weeks and on the day of rejection. Groups comprised six or seven rats. RESULTS: Donor alloantigen-pulsed bone marrow-derived dendritic cells (group V) significantly prolonged median composite tissue allograft survival time (32.0 days) compared with groups II (18.0 days, p = 0.0012), III (22.5 days, p = 0.0043), and IV (26.5 days, p = 0.0043). Splenic T cells in group V exhibited hyporesponsiveness to donor alloantigen in mixed leukocyte reaction. Interestingly, the graft muscle component in the bone marrow-derived dendritic cell-treated group (group V) showed significant reduction in mononuclear cell infiltration relative to group II (p = 0.0317). CONCLUSIONS: Donor alloantigen-pulsed recipient bone marrow-derived dendritic cells combined with transient T-cell-directed immunosuppression significantly prolonged composite tissue allograft survival across a full major histocompatibility complex barrier. This may represent the basis for a novel, clinically applicable strategy to promote composite tissue allograft survival with reduced systemic immunosuppression.

Transhemispheric functional reorganization of the motor cortex induced by the peripheral contralateral nerve transfer to the injured arm.

Peripheral nerve injury in a limb usually causes functional reorganization of the contralateral motor cortex. However, a dynamic process of the novel transhemispheric functional reorganization in the motor cortex was found in adult rats after transferring the seventh cervical nerve root from the contralateral healthy side to the injured limb. Initially the ipsilateral motor cortex activated the injured forepaw for 5 months after the operation. Then, both hemispheres of the cortex activated the injured forepaw, and finally the contralateral cortex exclusively controlled the injured forepaw. It is concluded an extensive functional shift occurred between two hemispheres based on neural plasticity in the CNS. The experimental results of the later lesions of the ipsilateral cortex suggest that maintaining transhemispheric functional reorganization does not depend on the corpus callosum, but depends on mechanisms involving central axonal sprouting. Possible mechanisms underlying the alternative changes in cortical functions were discussed in rats and in patients having similar operations.

The influence of pre-tensioning of meniscal transplants on the tibiofemoral contact area.

The purpose of the present study was to determine the effect of biological in-growth and pre-tensioning on the load transmission function of meniscal transplants. The ability of meniscal transplants to transfer load to the tibial plateau was measured in an animal model. Thirty-six sheep were divided into six groups: group A was the sham group, in group B a medial meniscectomy was performed, and in groups C-F a medial meniscal transplantation with an autograft was carried out. In groups C-F, different levels of pre-tensioning force were applied via bone tunnel sutures (C=0, D=20, E=40, and F=60 N, respectively). The animals were killed after 6 months. The excised knees were mounted in a materials testing machine at 30, 60, and 90 degrees of flexion, and loaded through the femoral axis to 500 N. A thin film pressure measuring transducer (K-scan, Tekscan) was positioned underneath the meniscus in the medial compartment in order to determine contact area and pressure. The mean contact pressure (MCP) of the sham group (A) and the groups with the transplanted meniscus (C-F) was significantly lower in relation to the meniscectomized knees (B). Significant increases in contact area and reductions in peak contact pressure were also observed. Only the meniscal transplantation group with 40 N (E) pre-tension consistently showed a significant or strong trend toward increased contact area, compared to the meniscectomized knees (B) at all flexion angles tested. All meniscal transplanted groups with the exception of the 0 N group (C) showed a significant reduction in peak contact pressure in comparison to the meniscectomized group (B). The results indicate that meniscal transplantation reduces the MCP on the tibial plateau independent of the level of intraoperative pre-tensioning. Furthermore, the menisci pre-tensioned to 40 N showed significantly increased contact area and reduced peak contact pressure in comparison to the meniscectomized knees at all flexion angles tested, and revealed results similar to those reported in the literature for meniscal allografts fixated with bone plugs.

[Apoptosis and its role in plastic surgery]. / Die Apoptose und ihre Bedeutung in der Plastischen Chirurgie.

Apoptosis and cell proliferation are the main mechanisms of cell homeostasis. The pathogenesis of approximately 70 % of all diseases results from an imbalance between these two counterparts. Therefore, research on apoptosis is a main target in biological and clinical fields. Many signalling pathways and proteins involved in their regulation have been characterized. In order to evaluate the relevance of apoptosis in plastic surgery, the literature was reviewed for its impact on ischemia and reperfusion concerning flap surgery as well as wound healing and angiogenesis. Furthermore, the relevance of apoptosis in ageing, allotransplantation and tumors was investigated. In all subsections of plastic surgery, a high impact was identified. More studies on the influence and regulation of apoptosis can bring further understanding on the disease patterns of plastic surgery and other specialties as well as the development of new therapeutic options. Research focusing on apoptosis is therefore an essential means for the advancement of and future trends in plastic surgery.

The role of donor and recipient in tissue implantation.

The relationships between embryonic stem and cambial cells in the ontogeny were evaluated on the basis of our data on organ embryogenesis and in vivo implantation of epithelial tissues and published data. We demonstrated the role of recipient tissues in the implantation process. Aseptic inflammation developing in response to the implant activates proliferation of the adjacent donor tissues. Proliferation and differentiation of the implanted donor tissues correspond to inflammation phases in the focus of implantation, are regulated by factors of the recipient organism, and are histogenetically determined.

Cyclic AMP elevates tubulin expression without increasing intrinsic axon growth capacity.

Exposing rat dorsal root ganglion (DRG) neurons to dibutyryl cAMP (db-cAMP) enables central branches to regenerate in the spinal cord by nullifying the ability of CNS myelin to inhibit elongation. A conditioning lesion (CL) promotes similar regeneration of central branches in the spinal cord by increasing neuronal cAMP levels. It is a matter of speculation whether any of the other effects of a CL are triggered by elevated cAMP. We found that like a CL, intraganglionic injection of db-cAMP increases the expression of growth-associated tubulin isotypes. However, unlike a CL, db-cAMP does not increase the velocity at which tubulin is delivered to the tips of growing axons by slow component b (SCb). db-cAMP also fails to increase intrinsic axon growth capacity enough to raise the rate of regeneration of peripheral branches in the sciatic nerve or enable central branches to elongate long distances in an environment free of all CNS inhibitors of elongation (i.e., a peripheral nerve graft transplanted into the spinal cord at the site of dorsal column transection). Thus, the increase in cAMP induced by a CL induces some, but not all, of the changes that may be necessary to increase intrinsic axon growth capacity.

In vitro physical stimulation of tissue-engineered and native cartilage.

Because of the limited availability of donor cartilage for resurfacing defects in articular surfaces, there is tremendous interest in the in vitro bioengineering of cartilage replacements for clinical applications. However, attaining mechanical properties in engineered cartilaginous constructs that approach those of native cartilage has not been previously achieved when constructs are cultured under free-swelling conditions. One approach toward stimulating the development of constructs that are mechanically more robust is to expose them to physical environments that are similar, in certain ways, to those encountered by native cartilage. This is a strategy motivated by observations in numerous short-term experiments that certain mechanical signals are potent stimulators of cartilage metabolism. On the other hand, excess mechanical loading can have a deleterious effect on cartilage. Culture conditions that include a physical stimulation component are made possible by the use of specialized bioreactors. This chapter addresses some of the issues involved in using bioreactors as integral components of cartilage tissue engineering and in studying the physical regulation of cartilage. We first consider the generation of cartilaginous constructs in vitro. Next we describe the rationale and design of bioreactors that can impart either mechanical deformation or fluid-induced mechanical signals.

Leech responses to tissue transplantation.

The aim of the present work is to describe histologically, histochemically and immunocytochemically, the sequence of events that lead to first and second set rejection of allo- or xenograft in leeches. Graft responses of leeches are comparable and are described following specific steps: inflammatory phase, rejection phase and granulation tissue formation (including re-epithelialisation, angiogenesis and fibroplasia).The responses to first and second graft in first set graft rejection as well as to the first transplant in second set graft experiments are identical and in the time span of a week all grafts are destroyed and disappear. In the second set graft rejection experiments the responses against the second transplant are markedly accelerated. The second graft shows massive structural alterations and it is rapidly rejected, within 3-4 days.Our results permit to highlight that in leeches there is a specific responsiveness of immune system similar to those described in highly divergent phyla.

Human endothelial progenitor cell-seeded hybrid graft: proliferative and antithrombogenic potentials in vitro and fabrication processing.

In this article, we show that human endothelial progenitor cells (EPCs) in circulating peripheral blood may be a novel cell source for a cell-incorporated engineered vascular graft. Cultures of human peripheral blood mononuclear cells collected by the density gradient technique developed highly proliferative EPC colonies, which expanded with culture time. The production rates of antiplatelet substances such as endothelial-type nitric oxide synthase and 6-keto-prostaglandin-F(1)-alpha were approximately one-third and approximately one-half of those of mature endothelial cells (ECs), respectively. On the other hand, the tissue-type plasminogen activator production rate of EPCs was almost the same as that of ECs. EPCs were seeded and cultured on a small-diameter compliant graft (inner diameter, 1.5 mm) made of microporous segmented polyurethane film coated with a photo-reactive gelatin layer, and subsequently subjected to hydrodynamic shear stress by ex vivo circulation. EPCs fully covering the graft elongated and aligned themselves with the direction of the flow, resulting in the production of an integrated EPC-engineered graft. These results indicate that EPCs, which have high proliferative potential and high antithrombogenic potential, comparable to those of ECs, are a suitable cell source for cardiovascular tissue engineering.

Emerging design principles in biomaterials and scaffolds for tissue engineering.

Biomaterials and scaffolds play an essential role in tissue engineering by guiding new tissue growth in vivo and in vitro. While adaptation of existing surgical materials has fulfilled some needs in the field, new applications demand better control of bulk properties such as degradation and of surface properties that control cell interactions. Advances in molecular cell biology are driving the incorporation of new biological moieties into materials, and a set of design principles based on quantitative analysis of key cellular processes involved in regeneration is emerging. At the same time, new materials-processing methodologies are emerging to allow fabrication of these fragile materials into devices appropriate for delivery.

Role of CD4+ and CD8+ T cells in early and late acute rejection of small bowel allograft.

BACKGROUND/PURPOSE: Results of small bowel transplantation remain unsatisfactory because of severe immune rejection. The current study aims to elucidate the role of activation of CD4+ and CD8+ T cells in early and late acute rejection of small bowel allograft and, hence, provide the immunologic basis for developing new therapeutic strategies. METHODS: We used an MHC fully mismatched (DA to Lewis) heterotopic rat small bowel transplant model and a unique FK506-based immunosuppressive regimen, which suppresses early acute rejection but does not prevent late acute rejection. Flow cytometric analysis was used to quantitate the number of activated CD4+ and CD8+ T cells in graft and host mesenteric lymph nodes. RESULTS: The survival (mean +/- SD) of intestinal allograft was significantly prolonged, from 6.6 +/- 0.84 days for the untreated group to 40.7 +/- 14.1 days for the FK506-treated group. Activation of CD4+ cells was suppressed significantly in the FK506-treated group on postoperative day 7 compared with the untreated group (29.4% +/- 3.55% v 52.83% +/- 11.9%; P <.01). Activation of CD8+ cells was similarly suppressed (31.5 +/- 10.34% v 48.53 +/- 14.34%; P <.05). Interestingly, at late acute rejection, activated CD4+ and CD8+ T cells remained at almost the same low levels as those on postoperative day 7 in the FK506-treated group. The spleen to body weight ratio was significantly increased in the untreated group (0.53 +/- 0.07), and slightly increased in the FK treated group (0.27 +/- 0.07, on postoperative day 7; 0.24 +/- 0.07 at late acute rejection) compared with the syngeneic group (0.18 +/- 0.02). CONCLUSION: The activation of CD4+ and CD8+ T cells was suppressed effectively by early potent immunosuppressive treatment resulting in prolonged survival of intestinal allograft. At late acute rejection, the CD4+ and CD8+ T cells remained at low-level activation status, in contrast to the surge of CD4+ and CD8+ activation during early acute rejection. This suggests that persistent T cell activation even at low level is sufficient to cause the late acute rejection eventually. A therapeutic strategy targeting these cells is needed for long-term engraftment.