Lung allograft rejection in the rat. II. Specific immunological properties of lung grafts.

The immunological mechanism of lung allograft rejection was studied in inbred rats, in order to explain the rapid progress of the rejection response against RT1-incompatible lung grafts. Histological appearances of the graft and of the recipient's spleen were studied, migration patterns of graft and recipient lymphocytes were assessed, and titers of circulating alloantibodies were determined. Histologically, we discriminated four phases of the rejection response in lung grafts: sequentially the latent, vascular, alveolar, and destruction phases. Early in the vascular phase, recipient lymphocytes primarily infiltrated the bronchus-associated lymphoid tissue (BALT) of the graft, causing a local immune response. Concurrent with these local rejection phenomena in the graft, a strong systemic immune response developed in the recipient's spleen, presumably induced by the great number of lymphocytes that migrated from the graft's BALT into the recipient's lymphoid tissues. We conclude that BALT facilitates a fast and intensive interaction between lung graft and recipient that is likely to accelerate the induction of the rejection response both locally in the graft and systemically in the recipient's lymphoid organs.

Lung allograft rejection in the rat. III. Corresponding morphological rejection phases in various rat strain combinations.

Rejection of RT1-incompatible lung grafts has been found in the study reported in our accompanying article to result in four consecutive morphological rejection phases: the latent, the vascular, the alveolar, and the destruction phase. The most prominent signs of rejection, however, occur early in the vascular phase in the bronchus-associated lymphoid tissue (BALT) of these grafts. In this study we investigated whether these four phases and the early rejection signs in BALT are universal phenomena of lung allograft rejection. Therefore, various donor-recipient combinations of inbred rat strains, incompatible for the MHC or for minor loci, were compared with respect to histological rejection phenomena--both in the lung graft and in the recipient's spleen--and alloantibody formation. The four rejection phases appeared sequentially in grafts of all combinations. Duration of the phases depended on the degree of histoincompatibility of the graft. Again, BALT was involved early in the rejection process. During the vascular phase a strong immune response developed in the spleen, and in the alveolar phase antibodies circulated in the blood. We conclude that these morphological rejection phases are universal phenomena of the rejection process against lung allografts in rats. Corresponding phenomena have been described for other species, even in immunosuppressed recipients. Based on these data, a new concept of the universal rejection process of lung allografts is postulated.

Lung allograft rejection in the rat. I. Accelerated rejection caused by graft lymphocytes.

To find out to what extent rejection of lungs differs from that of other organs, functional rejection of lung allografts was studied in five combinations of inbred rat strains. Rejection could be monitored accurately by perfusion scintigraphy, and equally well by chest roentgenography. The rejection of lung grafts was found to proceed remarkably fast, when compared with heart grafts, in combinations with strong RT1-incompatibilities. This accelerated rejection pattern could be converted into rejection at a normal pace by pretreatment of the donor with 10 Gy roentgen irradiation one day before transplantation. Donor pretreatment depleted the lung graft's bronchus-associated lymphoid tissue (BALT) of lymphocytes. When grafts were depleted of all other passenger cells as well--by retransplantation from a cyclosporine-treated intermediate host--they showed an even more reduced immunogenicity, probably because of the loss of donor-type dendritic cells. These results indicate that lymphocytes from the BALT of lung grafts are capable of accelerating the rejection response.

The combi-effect--reduced rejection of the heart by combined transplantation with the lung or spleen.

The term combi-effect was introduced to describe the phenomenon of a reduction in rejection of heart grafts after combined transplantation with the lung. In this study in rats we investigated whether the combi-effect was an immunological process and whether it could also be induced by combined transplantation of the heart with the spleen or with a lymphocyte-depleted spleen. Heart and spleen grafts were transplanted into the abdomen; left lungs were transplanted into the thorax of recipient rats. To deplete spleens of their lymphocytes, prospective donor rats were irradiated. Cyclosporine was injected once, on day 2 after transplantation. All heart allografts transplanted alone and treated with cyclosporine were rejected acutely (median survival time [MST] of 14.5 days). In contrast, after combined transplantation of a donor lung or spleen with the heart, almost all heart grafts survived indefinitely. Transplantation of a syngeneic lung or third-party spleen had little effect on heart graft survival (MST of 22.5 days and 26.5 days, respectively). Without cyclosporine treatment, combined transplantation with a donor lung or spleen hardly prolonged heart graft survival. Transplantation of a lymphocyte-depleted spleen with the heart induced a combi-effect in cyclosporine-treated rats that was somewhat weaker: only two of six hearts survived indefinitely. We conclude that in the combi-effect an immunological mechanism reduces rejection of the heart. This mechanism is probably generated by the lymphoid tissue (bronchus-associated lymphoid tissue in lung and white pulp in spleen) in the combined transplant.

Factors determining prolongation of rat heart allograft survival by perioperative injection of donor spleen cells.

Previously, we have shown that a perioperative injection of donor mononuclear cells in combination with cyclosporine treatment on day 2 after transplantation prolongs heart allograft survival in rats. In this study we determined whether the efficacy of this treatment was influenced by the same factors that have been shown to affect the efficacy of preoperative administration of donor cells. The effect of the following factors were investigated: dosage and repetition of the donor cell injection, viability of the donor cells, immunosuppressive drugs other than cyclosporine, and the rat strain combination. We found that there was an optimal dosage of donor cells; dosages of 4 x 10(7) or 1 x 10(8) cells gave the best heart graft survival. Repetition of the donor cell injection was not useful. Reducing viability of the cells by irradiation did not abrogate the prolonged graft survival, whereas killing of the cells did. Methylprednisolone, azathioprine, or cyclophosphamide in combination with the perioperative donor cell injection did not prolong heart graft survival in comparison with treatment with the drug only. The efficacy of this treatment was also influenced by the rat strain combination. In some combinations, this treatment prolonged graft survival, whereas in others an effect was absent or undetectable. Importantly, this treatment never adversely affected graft survival. We conclude that the efficacy of this treatment is influenced by similar factors as found for preoperative treatment with donor cells. A major advantage of this treatment over preoperative blood transfusions is that it avoids sensitization.

Airway pathology in the transplanted rat lung.

Bronchiolitis obliterans has emerged as the most significant long-term complication of human heart-lung transplantation. Possible causes include rejection, infection, altered bronchial circulation, and denervation. We attempted to assess the role of some of these possibilities by reviewing the airway histology in nonimmunosuppressed orthotopic rat left lung allografts in three strain combinations: BN-to-LEW (major histocompatibility complex [MHC]-incompatible) n = 27; (LEW X BN)F1-to-LEW, n = 11; and F344-to-LEW (minor loci-incompatible) n = 18. Fifteen syngeneic transplants (LEW-to-LEW) served as controls. After assigning the lungs to a rejection phase (latent, vascular, alveolar, or destructive), the airway pathology was specifically examined. In the latent phase, only changes attributable to transplantation per se were identified. In the vascular phase in the BN-to-LEW rats and (LEW X BN)F1-to-LEW rats, the bronchioles were surrounded by dense cuffs of activated lymphocytes. The lymphocytic infiltrate then progressively involved the lamina propria and epithelium, where it became associated with focal epithelial cell necrosis. Eventually the epithelium became ulcerated (alveolar phase), and the submucosa and luminal surface became replaced by granulation tissue, which frequently protruded into the lumen in a bronchiolitis obliterans pattern. In the destructive phase the changes were similar to those in the alveolar phase, but were more severe. In the F344-to-LEW rats the airway changes were less prominent, although the remainder of the lungs was at comparable phases of rejection. These changes were not observed in the right (nontransplanted) lungs or the control (LEW-to-LEW) lungs. The findings in these animals suggest that the process of rejection affects the airways and may result in posttransplantation bronchiolitis obliterans.

Late airway changes caused by chronic rejection in rat lung allografts.

Airway disease after lung or heart-lung transplantation is one of late major complications, affecting the prognosis of the transplants. Little is known about the causes of airway changes. We performed rat lung transplantation and investigated the late airway changes of the long-term surviving lung grafts: allografts, BN to Lewis; isografts, BN to BN rat. All recipients were treated with CsA. We found airway changes, i.e., mucosal ulceration, granulation, submucosal fibrosis, which was located in the large airways, in four of five allografted lungs. The lung isografts showed no pathological abnormalities. Immunopathological studies disclosed the localized expression of MHC class II antigens on the bronchial epithelium of the large airways where recipient type dendritic cells accumulated in the submucosa and CD4 positive predominant lymphocytes infiltrated. These findings support the idea that the late airway changes in lung transplants are caused by immunologically mediated chronic rejection.

Expression of class II major histocompatibility complex antigens by bronchial epithelium in rat lung allografts.

Variations in expression of class II major histocompatibility complex antigens on bronchial epithelial cells and vascular endothelium were investigated in normal rat lungs and allografted lungs during acute rejection and after cyclosporine (CsA) treatment. BN (RT1n) left lungs were transplanted into LEW (RT1l) recipients. Lungs were excised during acute rejection in untreated rats on postoperative days 1 through 5, and after CsA treatment (25 mg/kg on days 2 and 3) on days 5 and 100. Cryostat sections were examined for class II antigen expression with an immunoperoxidase technique, using various monoclonal antibodies. In the normal lung, class II antigens were not expressed by epithelial or endothelial cells. In the allografts, induction of class II antigens closely correlated with the rejection process: on day 2, the ciliated bronchial epithelium was locally positive; it became uniformly positive with increasing cellular peribronchial infiltration on days 3 and 4. CsA treatment prevented class II antigen expression to a certain extent, leaving the bronchial epithelium weakly positive at 100 days. Endothelial cells were invariably negative for class II antigens in all allografted lungs. The class II antigens expressed on the bronchial epithelial cells were of graft origin, except for recipient-type class II molecules found on the ciliated surface in CsA-treated animals. We conclude that expression of class II antigens by bronchial epithelium is the result of a bronchus-directed rejection process, and hypothesize that such a rejection process may have caused bronchiolitis obliterans in several of the patients with combined heart-lung transplants. Important is the observation that class II molecules can be present on the membranes of cells that do not themselves produce these antigens.

Lung transplantation in the rat. A morphometric analysis of the gas exchange region.

Single-lung transplantation in the rat provides a model that allows investigators to study immunologic, cellular, and morphologic changes associated with allograft rejection. We performed morphometric analysis of transplanted and nontransplanted lungs removed from recipients having received isografts, allografts, or hilus-stripping up to six months previously, and having received cyclosporine on the first postoperative day, the second postoperative day, the first five days, or not at all. When CsA was not administered, there was extensive and rapid destruction of the alveolar septa with consolidation and rejection of the transplanted lung within one week. In contrast, the allografts from rats treated with CsA were not obviously changed compared with the control lung. To evaluate whether or not these CsA-treated allografts had even subtle injury to alveolar septal cells, a morphometric analysis using transmission electron microscopy was used. There were no significant changes between control (nontransplanted or hilus-stripped) lungs and isografted or allografted lungs for most parameters measured. Exceptions included type I epithelial cell volume, which increased in rats treated with CsA on postoperative day 1 only, and the tissue component of diffusing capacity, which decreased in rats treated with CsA on postoperative day 2 only. We conclude that CsA treatment of rats given lung allografts effectively blocks the development of injury in the gas exchange region. The effect is achieved when the CsA is given during the first five days following transplantation in rats, and may be influenced by the timetable of administration and cumulative dosage.

Morphologic activation of lymphocytes in blood during rejection of heart and lung grafts in rats.

We investigated morphologic activation of lymphocytes in blood in a standardized, infection-free rat model and compared lymphocyte activation during rejection of heart grafts and that of lung grafts with other parameters of rejection. For heart grafts the other parameters were histology and palpation, and for lung grafts they were histology, bronchoalveolar lavage, and chest roentgenography. During acute rejection of heart grafts, lymphocyte activation in blood increased when histology of the heart grafts showed already moderate-to-severe rejection with myocyte necrosis. Lymphocyte activation in blood detected acute heart rejection clearly later than histology but somewhat earlier than palpation. During acute rejection of lung grafts, lymphocyte activation in blood increased when histology of the lung grafts showed the (early) vascular phase of rejection, without apparent tissue damage. Lymphocyte activation in blood detected acute lung rejection only slightly later than histology, at approximately the same time as bronchoalveolar lavage and earlier than chest roentgenograms. Lymphocyte activation was higher during acute lung rejection than during acute heart rejection. During "chronic" rejection of long-surviving heart grafts and lung grafts, lymphocyte activation in blood did not increase consistently. The early and strong increase of morphologic activation of lymphocytes in blood during acute lung rejection may imply for clinical transplantation that monitoring of lymphocyte activation in blood is more useful for early detection of acute rejection after lung transplantation than after heart transplantation.

Inadequate antibody response against respiratory viral infection in long-surviving rat lung allografts.

Lung transplant recipients suffer from a high number of viral infections. It has been suggested that the defense against viral infections is impaired in lung transplants. Therefore, we investigated in rat lung transplants whether antibody responses against an intrapulmonary viral infection were impaired in 3 groups of rats with: (1) BN-to-LEW allogeneic lung transplants, (2) LEW-to-LEW syngeneic lung transplants, and (3) nontransplanted LEW lungs. All rats (including those with nontransplanted, normal lungs) were treated with cyclosporine on days 2 and 3 after operation; this treatment is adequate to induce permanent graft acceptance of the allografts. Six months after transplantation, viral infections with Sendai virus (parainfluenza type I) were induced intratracheally. At day 0, immediately before infection, and at days 4, 7, 21, and 56 after infection, 4 rats in each group were killed for histological evaluation of the lungs. The number of antibody-positive cells in the bronchus-associated lymphoid tissue (BALT) in the lungs and in the spleen, and presence of the virus in the lungs were determined by immunohistology. Serum antibody titers were followed for 56 days after infection. The allogeneically transplanted lungs failed to respond adequately against the virus: the number of antibody-positive cells in the BALT did not increase after infection, serum antibody titers were hardly detectable, and virus was present in the airways of the lungs up to day 21 after infection. In contrast, in the syngeneically and nontransplanted lungs, the number of antibody-forming cells in the BALT increased steeply until day 7, serum antibody titers rose until day 14, and virus could be detected only on day 4 after infection. This study shows that in rat lung allografts, both the local antibody production in the BALT and the systemic antibody response against a respiratory viral infection are inadequate. As a consequence, the virus is present longer in these allografted lungs and can exert its damaging effect over a longer period of time. These results may explain why lung transplants are so susceptible to viral infections.

Improved healing of small-caliber polytetrafluoroethylene vascular prostheses by increased hydrophilicity and by enlarged fibril length. An experimental study in rats.

This study was undertaken to test whether increasing the hydrophilicity of small-caliber polytetrafluoroethylene vascular prostheses by alcohol pretreatment or increasing their fibril length might improve their healing without affecting their patency. Polytetrafluoroethylene vascular prostheses (length 1 cm, inside diameter 1.2 mm) (1) with a fibril length of 30 microns (control group; n = 18), (2) pretreated with alcohol (n = 18), or (3) with a fibril length of 60 microns (n = 18) were implanted into the abdominal aorta of rats. The prostheses were evaluated by means of routine light and scanning electron microscopy during a 6-week period after implantation. All prostheses were patent at harvesting. On implantation, the control polytetrafluoroethylene vascular prostheses were only scarcely covered with platelets. At 6 weeks they had healed in a small area adjacent to the anastomoses only. In contrast, both the alcohol-pretreated polytetrafluoroethylene prostheses and the polytetrafluoroethylene prostheses with a fibril length of 60 microns were completely covered by a thin clot layer on implantation. At 6 weeks after implantation these prostheses had almost completely healed as a result of organization of the thin clot layer by ingrowth of both endothelial and smooth muscle cells. These results demonstrate that increasing hydrophilicity of polytetrafluoroethylene vascular prostheses by alcohol pretreatment or enlarging their fibril length improves their healing by induction of a thin luminal clot layer. This clot layer provides a suitable matrix for ingrowth of both endothelial and smooth muscle cells and does not lead to thromboembolic complications.

Low-dose and high-dose aprotinin improve hemostasis in coronary operations.

Prophylactic aprotinin therapy has become a popular method to reduce bleeding associated with cardiac operations. Today essentially two dose regimens are used, a high-dose regimen with administration throughout the complete operative procedure and a low-dose regimen with administration only during bypass. In unblinded studies both regimens were found to be equally effective. This double-blind placebo-controlled study in 115 patients undergoing elective coronary artery bypass grafting was done to confirm these results without potential investigator bias. Intraoperative hemoglobin loss was significantly reduced (p < 0.01) by 42% in the high-dose group and by 17% in the low-dose group compared with loss in control subjects. Blood loss 6 hours after operation was 377 ml in the low-dose and 266 ml in the high-dose group compared with 630 ml in the placebo group (p < 0.05 and p < 0.001, respectively). The average number of transfusions with packed red blood cells was reduced 31% in the low-dose group and 45% in the high-dose group, but the reductions were not significant. In a subgroup of patients, markers for coagulation and fibrinolysis were studied to investigate whether a different extent of activation existed. Fibrinolysis as measured by D-dimer levels was completely inhibited by the high-dose regimen, but was only partly suppressed in the low-dose group as compared with findings in the placebo group. Thrombin generation during cardiopulmonary bypass as reflected by F1 + 2 levels was lower in patients treated with aprotinin, but the difference was not significant. Concentrations of thrombin inactivated by antithrombin III were not different between the groups. The observation that low-dose aprotinin significantly improved hemostasis but did not inhibit hyperfibrinolysis supports our previous finding that low-dose aprotinin mainly protects platelet adhesive function. The better result obtained with high-dose aprotinin may indicate the contribution of hyperfibrinolysis to bleeding after cardiopulmonary bypass. Because high-dose aprotinin is administered outside the period of full heparinization and might therefore increase the risk of thromboembolic complications, we propose a modification of the low-dose schedule to increase aprotinin levels sufficient for plasmin inhibition before release of the aortic crossclamp.

Arterial wall regeneration in small-caliber vascular grafts in rats. Neoendothelial healing and prostacyclin production.

Clinically available synthetic graft materials frequently fail when used as a small-caliber arterial substitute. Therefore, we developed a new type of graft material, prepared from a mixture of polyurethane and poly-L-lactic acid, to be used as a scaffold for the regeneration of the arterial wall. In this study microporous, compliant, biodegradable polyurethane/poly-L-lactic acid grafts (n = 16) and polytetrafluoroethylene grafts (n = 16) were implanted in the rat abdominal aorta and evaluated 3, 6, and 12 weeks after implantation. First, we evaluated the extent of neoendothelial healing (n = 8) by means of light microscopy and scanning electron microscopy. Next, we studied the ability of the neoendothelial cells to produce prostacyclin (n = 8) by means of bioassay for prostacyclin and radioimmunoassay for its stable hydrolysis product, 6-oxo-prostaglandin F1 alpha. There were no significant differences between the two graft types in the amount of prostacyclin production per unit graft area covered with neoendothelium, and this amount was the same as for normal endothelium. However, the polytetrafluoroethylene grafts showed incomplete neoendothelial healing, even after 12 weeks of implantation, in contrast to the polyurethane/poly-L-lactic acid grafts. The better healing characteristics of the polyurethane/poly-L-lactic acid grafts ensured the fast development of a complete neoarterial wall, possessing strength, compliance, and thromboresistance equivalent to normal arterial wall tissue. These results demonstrate that arterial wall tissue regeneration in polyurethane/poly-L-lactic acid grafts may open new perspectives in the field of arterial reconstructive surgery.

Blood activation during neonatal extracorporeal life support.

Cardiopulmonary bypass for heart operations is associated with a whole body inflammatory reaction. The main factors involved in this reaction are the contact system and the complement system. The activation of the contact system is considered mainly responsible for impaired hemostasis because it affects platelet function. The activation of the complement system is considered the main cause for organ dysfunction, particularly of the lung, due to activation of leukocytes. This study in 10 neonates was undertaken to evaluate if there are effects of activation of the contact and the complement systems in neonatal extracorporeal life support comparable to those during cardiopulmonary bypass for cardiac operations. Two periods of blood activation during extracorporeal life support could be distinguished. The initial blood-material interaction at the onset of extracorporeal life support resulted in activation of both the contact and the complement systems. The contact activation was apparent by elevated factor XIIa-C1 esterase inhibitor complexes, decreased kallikrein inhibitory capacity, thrombin-antithrombin III formation, and moderate generation of fibrin(ogen) degradation products. The complement activation was characterized by elevated C3a, decreased leukocyte count, elastase release, and tumor necrosis factor-alpha production. This initial activation pattern subsided by 24 hours. A second activation period was observed 72 hours after the onset of extracorporeal life support, which was characterized only by increased clotting and fibrinolytic activity while no activation of the complement system was observed. We conclude that the initial activation pattern in extracorporeal life support is similar to that observed during cardiopulmonary bypass for cardiac operations. The contact activation that affects platelets might explain the continuous platelet consumption observed during extracorporeal life support. In this period, as in cardiopulmonary bypass, aprotinin given in the pump prime might be effective to prevent platelet consumption and impairment of hemostasis also in extracorporeal life support. The complement activation and leukocyte inflammatory reaction during the initial period are able to cause a capillary leak syndrome and might therefore explain the frequently observed temporary compromised lung function in extracorporeal life support. This reaction, as in cardiopulmonary bypass, might be reduced by the use of specific drugs or heparin coating also in extracorporeal life support. The cause of the second period of activation during extracorporeal life support requires further studies before adequate measures can be recommended.

Hemostatic function of aspirin-treated platelets vulnerable to cardiopulmonary bypass. Altered shear-induced pathway.

The impaired hemostasis of aspirin-treated patients is an annoying problem during and after cardiopulmonary bypass. The hemostatic function of platelets comprises two mechanisms: the shear-induced and the cyclooxygenase pathways. Because the latter is inhibited in aspirin-treated patients, the hemostatic function depends mainly on the former pathway. To investigate the effect of cardiopulmonary bypass on the shear-induced pathway, a double-blind study of preoperative aspirin treatment (325 mg) and placebo was conducted in 40 patients undergoing coronary artery bypass grafting. Postoperative blood loss was higher in the aspirin-treated patients than in the placebo-treated patients (p < 0.05). The shear-induced hemostasis was monitored by the in vitro bleeding test (Thrombostat), which mimics bleeding through an injured arteriole. The shear-induced pathway of aspirin-treated platelets was not affected before cardiopulmonary bypass, but it was impaired more during the operation (p < 0.01) and remained worse afterward (p < 0.05), compared with that of placebo-treated platelets. The inhibitory effects of aspirin on thromboxane production and on collagen-induced platelet aggregation remained throughout the operation. In aspirin-treated platelets, the aggregation capacity induced by adenosine diphosphate was inhibited before the operation (p < 0.05) and showed substantial recovery during the operation (p < 0.05). These results suggest that the shear-induced pathway of aspirin-treated platelets is more vulnerable to cardiopulmonary bypass than the pathway in normal platelets and causes severe impairment of hemostasis afterward.

Sequential studies of arterial wall regeneration in microporous, compliant, biodegradable small-caliber vascular grafts in rats.

Microporous, compliant, biodegradable vascular grafts prepared from a mixture of polyurethane (95% weight) and poly-L-lactic acid (5% weight) can function as a temporary scaffold for the regeneration of the arterial wall in small-caliber arteries. This study was undertaken to document the sequential events leading to this regeneration. Therefore, polyurethane/poly-L-lactic acid vascular grafts were implanted into the abdominal aorta of rats (N = 28) and were harvested at regular intervals from 1 hour up to 12 weeks after implantation. The implants were evaluated by means of light and electron microscopy. At each time of harvesting, the implants were patent and showed arterial pulsations. No stenosis or dilatation was observed. Endothelial cells grew from the adjacent aortic intima across the anastomoses, from day 6 onward, to form an almost complete neointima after 6 weeks of implantation. Smooth muscle cells also grew from the adjacent aortic media over the graft lattice through the platelet-fibrin coagulum from day 6 onward. The smooth muscle cells, predominantly longitudinally arranged at week 6, but also circularly arranged in some areas at week 12, formed a neomedia in which elastic laminae regenerated. Polymorphonuclear leukocytes and monocytes initially invaded the graft lattices. Fibroblasts, histiocytes, and capillaries grew from the perigraft tissue into the polyurethane/poly-L-lactic acid lattices from day 6 onward, which resulted in the formation of a neoadventitia. The polyurethane/poly-L-lactic acid lattices started to disintegrate from day 12 onward. The regenerative processes in the disintegrating polyurethane/poly-L-lactic acid grafts resulted in the formation of neoarteries, which were of sufficient strength, compliance, and thromboresistance to function as small-caliber arterial substitutes.

Rapid endothelialization of vascular prostheses by seeding autologous venous tissue fragments.

A method was developed to obtain rapid endothelialization of a fabric vascular prosthesis by seeding autologous venous tissue fragments into its wall. In an animal study, complete endothelialization was observed in the entire inner surface of the prosthesis within 2 weeks after implantation. A piece of peripheral vein was minced with scissors and then stirred into saline to create a tissue suspension. This suspension was enmeshed into the wall of a highly porous fabric vascular prosthesis by repeated pressurized injections with a syringe. The prostheses (7 mm inside diameter and 5.7 cm in length), seeded with tissue fragments, were implanted into the descending thoracic aorta of 25 dogs, and they were removed from 1 hour to 2 months after implantation. Twenty-five prostheses, preclotted with fresh blood, were used as control prostheses. In the seeded graft, a thin fibrin layer covered the inner surface just after implantation, but countless numbers of endothelial cells migrated from the fragments and came up to the luminal surface like multiple "mushrooms" under the fibrin layer. Smooth muscle cells made multiple layers underneath the endothelial cell layer. The healing proceeded equally at every part. By this active migration and proliferation, the inner surface was completely healed within 2 weeks.

Aprotinin protects platelets against the initial effect of cardiopulmonary bypass.

Remarkable improvement in hemostasis after cardiopulmonary bypass has been achieved by treatment with the proteinase inhibitor aprotinin, but the mechanism is still unclear. The present study is designed to elucidate the importance of platelet adhesive (glycoprotein Ib) or aggregatory (glycoprotein IIbIIIa) receptors on this hemostatic function in cardiopulmonary bypass and its improvement by aprotinin treatment. To determine whether the first pass of blood through the circuit or a continuous proteolytic attack is the main cause of platelet damage, we gave two different dose regimens of aprotinin treatment to patients undergoing coronary artery bypass grafting. Part I of the study consisted of a double-blind trial on 60 patients. Patients received placebo or aprotinin infusion (total 6.10(6) KIU) before and during bypass. A consecutive group of 22 matching patients received one single bolus of aprotinin in the pump prime (2.10(6) KIU). Blood samples were collected before and during operation to assess the effect of bypass and aprotinin on platelets and the activation of the various proteases in relation to hemostasis expressed in blood loss and blood requirements. The adhesive platelet membrane Ib glycoproteins were decreased by 50% in the untreated patients within 5 minutes of cardiopulmonary bypass and remained low during bypass, whereas glycoprotein Ib did not decrease in either group of aprotinin-treated patients. The platelet membrane IIbIIIa glycoproteins did not significantly change during bypass in either group, but fibrinogen binding to these receptors improved significantly in the 6.10(6) KIU aprotinin-treated group at the end of bypass as compared with initial values. The high continuous dose of 6.10(6) KIU aprotinin inhibited the clotting and kallikrein/kinin system throughout the operation; the pump prime dose of 2.10(6) KIU inhibited these systems only initially. Although the fibrinolytic activity was effectively inhibited in both aprotinin groups, fibrinolytic activity became apparent only at the end phase of bypass in the placebo group. However, improved hemostasis was observed intraoperatively from the start of bypass and resulted in a 40% lower blood loss intraoperatively and postoperatively and consequently a 40% lower total blood requirement in the aprotinin-treated patients than in the untreated patients. Our results therefore demonstrate that the improved hemostasis during and after bypass in patients treated with aprotinin has specifically to be attributed to a preserved adhesive capacity of platelets that was affected in the first pass of blood through the cardiopulmonary bypass circuit.

Reimplantation response in isografted rat lungs. Analysis of causal factors.

The function of transplanted lungs may be critically impaired in the early postoperative period by the reimplantation response. Several factors of the transplantation procedure, such as disruption of hilar structures (hilar stripping), stenotic anastomoses, and graft ischemia, are considered to cause this reimplantation response. In this study the individual contributions of these factors have been analyzed in rats, after isogeneic transplantation or hilar stripping of left lungs. Marck's technique for orthotopic transplantation of the left lung in rats was refined so that an 85% postoperative survival rate was achieved. Transplanted and hilar-stripped lungs were investigated by lung perfusion scintigraphy and chest roentgenography at regular intervals up to 168 days after operation. Macroscopic and histologic morphology was examined at corresponding intervals. Our results show that perfusion and ventilation of lung grafts are independently affected by distinct factors of the transplantation procedure. Hilar stripping did decrease graft perfusion transiently. Permanent decrease of perfusion was found to be caused by stenosis of the anastomosed pulmonary artery. Hilar stripping also impaired ventilation, by causing interstitial and alveolar edema. After transplantation, edema and consequent impairment of ventilation were aggravated by graft ischemia, proportionally to its duration. Our improved technique for transplantation of left lungs in rats provides a new opportunity for investigating the immunologic problems of lung transplantation.