Relevance of maintenance triple-drug immunosuppression to bridle the amplification of rat cytomegalovirus infection after experimental lung transplantation.

Immunosuppressive therapy required to treat rejection after lung transplantation (LTx) contributes significantly to the pathogenesis of cytomegalovirus (CMV) infection and disease. In a weak allogeneic left LTx model in the rat (Fisher 344 [F344] to Wistar Kyoto [WKY] rats) we analyzed the influence of acute CMV infection on postoperative day (POD) 3, with application of standard triple-drug immunosuppression (TD-IS) (cyclosporin A, azathioprine, prednisolone) on late outcome after LTx. Native right lungs and syngeneic grafts (WKY to WKY) served as controls. Rats were sacrificed on POD 15, 30, 60, and 100. TD-IS completely prevented acute and chronic rejection in non-infected rats. Allografts of CMV-infected rats treated with TD-IS showed only mild perivascular infiltrations in 6/10 rats (POD 15 and 30), which persisted up to POD 100 in 4/10 rats. In the long-term course, mild isolated interstitial and alveolar changes were found in 40% of these animals. In conclusion, rat CMV infection partially neutralized the immunosuppressive effect of TD-IS. However, an amplification of CMV infection under TD-IS can be controlled and does not result in fatal outcome.

Increase of MLC sensitivity by elimination of a non-adherent responder cell subpopulation with anti-macrophage serum.

A specific rabbit anti-rat macrophage antiserum (SAM) was prepared with a cytotoxic reactivity pattern complementary to that of a specific anti-lymphocyte serum. This was used to characterise adherent and non-adherent spleen cell subpopulations in mixed lymphocyte cultures. Adherent SAM+ cells reacted as accessory cells whereas non-adherent SAM+ cells were suppressors. Selective elimination thus achieved resulted in a highly significant increase of MLC reactivity in certain strain combinations and in conversion from non-reactivity to reactivity in others.

Immune reactivity after high-dose irradiation.

Immune reactivity after total-body irradiation was investigated in rats using skin graft rejection as the indicator system. After sublethal irradiation with 10.5 Gy (approximately 50% lethality/6 weeks) the rejection of major histocompatibility complex allogeneic skin grafts was delayed significantly compared with nonirradiated control animals (28 versus 6.5 days). In contrast, skin grafts were rejected after 7.5 days in sublethally irradiated animals and 7 days in lethally irradiated animals if additional skin donor type alloantigens--namely, irradiated bone marrow cells--were given i.v. either simultaneously or with a delay of not more than 24 hr after the above conditioning regimen. These reactions were alloantigen-specific. They were observed in six different strain combinations with varying donors and recipients. Starting on day 2 after irradiation, i.v. injection of bone marrow gradually lost its effectivity and skin grafts were no longer rejected with uniform rapidity; skin donor marrow given on days 4 or 8 did not accelerate skin graft rejection at all. These data show that for approximately 1-2 days after high-dose total-body irradiation rats are still capable of starting a vigorous immune reaction against i.v.-injected alloantigens. The phenomenon of impaired rejection of skin grafted immediately after high-dose irradiation appears to result from the poor accessibility of skin graft alloantigens during the early postirradiation phase when vascularization of the grafted skin is insufficient.

Functional characterization of prethymic T cells committed to alloreactivity.

The results of previous experiments on MHC fully allogenic bone marrow transplantation (BMT) in nonthymectomizd recipients indicated that anti-MHC alloreactivity starts to become irreversibly committed at the prethymic level. This is a matter of some controversy. Since it is possible that conflicting results depend on the methods chosen, we reexamined our previous results by applying two new approaches. Adult thymectomized (ATX) Balb/c mice received a syngeneic fetal thymus either 3 weeks before or 3 weeks after lethal irradiation and reconstitution with C57BL/6 BM incubated in antiserum. Since monoclonal antibodies such as anti-Thy 1 are of limited value for investigations of the above type (Thy 1 antigen crosses the prethymic/thymic border), we used two highly selective, excessively cytotoxic xenoantisera for incubation of the donor BM--either a specific anti-T cell serum (SAT) that eliminated only mature T cells, or a specific antilymphocyte serum (SAL) that reacted additionally with a subset of prethymic T cells (PTC). In both experimental approaches the results were similar: Recipients of SAT-BM developed antihost reactivity, in contrast to recipients of SAL-BM. SAT-BM recipients became immunodeficient, whereas SAL-BM chimeras were immunocompetent. Late mortality was observed only following SAT treatment. Preliminary morphological findings in the lymphoid tissue of BM recipients agree fully with the functional observations. We conclude that the data confirm our previous results in nonthymectomized BM recipients--i.e., PTCs initiate antihost reactivity in MHC fully allogeneic BMT--and PTC commitment is thymus/thymus factor independent. These conclusions are discussed with regard to the problems of MHC allogeneic clinical BMT.

Comparison of gamma-interferon and alloantigen-induced T cell factors in the induction of MHC class II antigen expression and in the modulation of the immunogenicity of lymphocyte-free rat bone marrow.

In a rat model, we compared the effects of various soluble products released by T cells, such as the unspecifically acting gamma-interferon or the newly detected alloantigen-induced factors that specifically act on nonlymphoid, hemopoietic bone marrow cells. We found two types of reactivity patterns with regard to the induction of MHC class II antigen expression on these cells. The very same patterns could be demonstrated when we investigated the modulation of their stimulatory capacity, i.e., their immunogenicity in a T proliferation assay. These findings are discussed in relation to the increasing incidence of immunologically mediated graft rejections in clinical bone marrow transplantation following T cell purging.

Effect of post-transplant methotrexate, cyclosporin A and prednisolone on graft rejection after allogeneic bone marrow transplantation.

Methotrexate, cyclosporin A and prednisolone have been shown to improve graft survival rates in solid organ transplantation. However, little is known concerning their capacity to promote lasting engraftment of allogeneic bone marrow. Therefore, we tested these agents in LEW rats receiving MHC-mismatched marrow after pretreatment with a myeloablative dose of busulfan plus different doses of total body irradiation (TBI). To avoid mortality due to graft-versus-host reaction (GHVR), F1(CAP x LEW) marrow was transferred. Hematological parameters were determined twice weekly to monitor engraftment and rejection. The pretreatment was lethal but not sufficiently immunosuppressive to ensure lasting engraftment in all animals. Thus, post-transplant immunosuppressive protocols could be evaluated for their capacity to improve engraftment rates. Standard clinical doses of methotrexate (0.25 mg/kg i.p. day 1, 3, 6, 11, 18, 25), cyclosporin A (10 mg/kg orally day 0-28) and prednisolone (1 mg/kg i.p. day 0-28) were administered and proved to be of nearly equivalent toxicity in our system. All three agents failed to allow engraftment after busulfan alone. After additional conditioning with 1.5 Gy of TBI, methotrexate and cyclosporin A reduced the rejection rate from 100% to 59% and 70%, respectively. When 3 Gy of TBI were added to busulfan, cyclosporin A and prednisolone were able to reduce the rejection rate from 67% to 33% and 39%, respectively, whereas 0.12 and 0.25 mg/kg methotrexate completely prevented graft rejections. After cessation of cyclosporin A therapy, late secondary rejections were frequently observed. These results demonstrate that postgrafting immunosuppression with protocols conventionally used for the prophylaxis of GVHR is able to facilitate lasting engraftment of MHC-mismatched bone marrow.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of obliterative bronchiolitis after allogeneic rat lung transplantation: implication of acute rejection and the time point of treatment.

BACKGROUND: Chronic allograft failure represents the major cause of late morbidity and mortality after solid organ transplantation. Despite the pathological and clinical changes of this disease being well-described, the etiology and the causative factors are still under discussion. Several clinical, as well experimental studies, emphasize the significance of acute rejection. In rat model of left lung allo-transplantation (F344-to-WKY) the influence of acute rejection (AR) on the development of chronic rejection (CR) was studied. METHODS: In Group I (n = 25) no immunosuppression was used, while methylprednisolone (MP) (10 mg/kg) was applied in Group II (n = 20) in the early phase of AR on postoperative Days 9, 10, 11 and in Group III (n = 20) during AR on Day 14, Day 15, Day 16. The rats were sacrificed on Day 5, Day 15/20, Day 30, Day 60, Day 100 and following HE-staining the extend of AR as well CR was graded according to the working formulation of The International Society of Heart and Lung Transplantation. RESULTS: In Group I, AR was found at Day 15 and Day 30 which resolved spontaneously and resulted in CR on Day 60 and Day 100. In Group II, signs of AR were less evident on Day 20, while mild AR persisted on Day 30 and Day 60. On Day 100, normal lung structure was found in all rats. The recipients of Group III showed decreased signs of AR in the early course, however, severe CR was found on Day 60 and Day 100. Extensive airway inflammation with destruction of the subepithelial layer of the smaller airways resulted in severe early obliterative bronchiolitis. CONCLUSIONS: Untreated severe AR in the early course after lung transplantation results in CR in the F344-to-WKY model. Preventive treatment with MP during the early phase of AR clearly diminishes the degree of AR and the graft recovers completely without any evidence of CR. Late application of steroids during the zenith of AR is successful to control the extent of AR, however, it fails to prevent CR.

Short-course cyclosporin A therapy for definite allograft valve survival immunosuppression in allograft valve operations.

This study was designed to determine the effect of short-course cyclosporin A therapy (10 mg/kg daily for 14 days) on allograft valve survival across the histocompatibility barriers in the following rat models; (1) syngeneic Lewis to Lewis (herein referred to as autografts), (2) weakly allogeneic AS to Lewis (RT1 compatible, non-RT1-incompatible), and (3) strongly allogeneic CAP to Lewis (RT1 and non-RT1-incompatible). Cyclosporin A-treated and untreated recipient animals (Lewis) received allovital and antibiotic-treated viable allografts implanted into the infrarenal aorta. Second-set skin grafting was performed 3 weeks after heterotopic valve implantation to test for immunogenicity and presensitization. The animals (Lewis) were sacrificed serially on days 20, 50, 100, and 150 for immunofluorescence study using mouse monoclonal antibodies (OX6) directed at class II endothelial surface antigens. The allografts in weakly allogenic strains showed no humoral response under a short course of cyclosporin A. The cyclosporin A-untreated allovital grafts and the viable (antibiotic-treated) valves demonstrated fibrocalcification on the 100th and 150th postoperative days, respectively. In conclusion, it seems that a short course of nontoxic immunosuppression could arrest allograft rejection and thus prevent early degeneration of allografts. Furthermore, antibiotic-treated viable allografts seemed to be more durable than allovital grafts.

Irradiation of groups of mice and rats. Studies on the homogeneity of dose distribution in the irradiation field of a Co-60 source.

Data are presented on the dose distribution pattern in an irradiation field for the irradiation of groups of small rodents as a preconditioning regimen for experimental bone marrow transplantation. The consequences of this pattern are discussed.