Acute rejection of experimental lung allografts: Characterization of intravascular mononuclear leukocytes

Conjunctival infiltrates and cytokines in an experimental immune-mediated blepharoconjunctivitis rat model

Purpose

To characterize the histopathological and immunological findings of a rat model of allergic blepharoconjunctivitis (BC) and demonstrate its potential utility for the assessment of BC therapies.

Methods

Sprague-Dawley (SD) rats were immunized with ovalbumin (OVA) and topically challenged with OVA (BC group) or PBS (control group), while a corticosteroid group was pre-treated with triamcinolone acetate 24 h before the challenge. Morphological features were evaluated and tissues were harvested for histological, flow cytometry and cytokine analysis.

Results

The BC group rats developed eyelid excoriations, redness, and conjunctival edema 24 h after the OVA challenge, while corticosteroid pre-treated and PBS-challenged rats were unaffected. The BC features were reduced despite repeated challenges for 5 days. Massive immune cell infiltration was observed in conjunctivae of BC rats, while no significant infiltration was seen in the other groups. Populations of T cells, mono-macrophages, neutrophils, and NK cells made up more than 77% of CD45⁺7AAD^- cells in the conjunctival tissues. T cell proportions were increased at 96 h compared to 24 h post-challenge, while macrophages decreased during the same time period. Eosinophils and intraepithelial neutrophils were detected in the BC rats, but not in the PBS and corticosteroid groups. BC eyes had significantly higher levels of IFN-γ and IL-2, while IL-4 and IL-6 levels were similar to controls.

Conclusion

A robust BC response was detected in this rat model which was suppressed by corticosteroid pre-treatment. Immune cell composition and cytokine profiles changed over time.

CD43Lo classical monocytes participate in the cellular immune response to isolated primary blast lung injury

BACKGROUND

Understanding of the cellular immune response to primary blast lung injury (PBLI) is limited, with only the neutrophil response well documented. Moreover, its impact on the immune response in distal organs remains poorly understood. In this study, a rodent model of isolated primary blast injury was used to investigate the acute cellular immune response to isolated PBLI in the circulation and lung, including the monocyte response, and investigate distal subacute immune effects in the spleen and liver 6 hours after injury.

METHODS

Rats were subjected to a shock wave (~135 kPa overpressure, 2 ms duration) inducing PBLI or sham procedure. Rat physiology was monitored, and at 1, 3, and 6 hours thereafter, blood, lung, and bronchoalveolar lavage fluid (BALF) were collected and analyzed by flow cytometry, enzyme-linked immunosorbent assay, and histologic examination. In addition, at 6 hours, spleen and liver were collected and analyzed by flow cytometry.

RESULTS

Lung histology confirmed pulmonary barotrauma and inflammation. This was associated with rises in CXCL-1, interleukin 6 (IL-6), tumor necrosis factor α and albumin protein in the BALF. Significant acute increases in blood and lung neutrophils and CD43Lo/His48Hi (classical) monocytes/macrophages were detected. No significant changes were seen in blood or lung "nonclassical" monocyte and in natural killler, B, or T cells. In the BALF, significant increases were seen in neutrophils, CD43Lo monocyte-macrophages and monocyte chemoattractant protein-1. Significant increases in CD43Lo and Hi monocyte-macrophages were detected in the spleen at 6 hours.

CONCLUSION

This study reveals a robust and selective response of CD43Lo/His48Hi (classical) monocytes, in addition to neutrophils, in blood and lung tissue following PBLI. An increase in monocyte-macrophages was also observed in the spleen at 6 hours. This profile of immune cells in the blood and BALF could present a new research tool for translational studies seeking to monitor, assess, or attenuate the immune response in blast-injured patients.

The Selective JAK1/3-Inhibitor R507 Mitigates Obliterative Airway Disease Both With Systemic Administration and Aerosol Inhalation

BACKGROUND

The efficacy of selective Janus kinase 1/3 inhibitor R507 to prevent obliterative airway disease was analyzed in preclinical airway transplantation models.

METHODS

Orthotopic trachea transplantations were performed between Lewis donors and Brown Norway rat recipients. Oral everolimus (4 mg/kg once per day) or oral respective inhaled R507 (60 mg/kg twice per day, each) was used for immunosuppression. Grafts were retrieved after 6 or 60 days. Toxicity and anti-inflammatory effects of R507 were analyzed on human airway epithelial cells.

RESULTS

In 6-day animals, oral and inhaled R507 more potently diminished mononuclear graft infiltration than everolimus and preserved ciliated pseudostratified columnar respiratory epithelium. Everolimus and R507 similarly suppressed systemic cellular and humoral immune activation. In untreated rats, marked obliterative airway disease developed over 60 days. Oral and inhaled R507 was significantly more effective in reducing airway obliteration and preserved the morphology of the airway epithelium. Luciferase-positive donors revealed that a substantial amount of smooth muscle cells within the obliterative tissue was of donor origin. Only everolimus but not R507, adversely altered kidney function and lipid profiles. The R507 aerosol did not show airway toxicity in vitro but effectively suppressed activation of inflammatory signaling pathways induced by IL-1β.

CONCLUSIONS

The Janus kinase 1/3 inhibitor R507 is a very well-tolerated immunosuppressant that similarly diminished obliterative airway disease with systemic or inhaled administration.

Non-neuronal neuropeptide Y and its receptors during acute rejection of rat pulmonary allografts

This study tested the hypothesis that neuropeptide Y (NPY) and NPY receptors 1 (Y1) and 2 (Y2) participate in lung allograft rejection. Inflammation in grafts may include interaction between blood leukocytes and graft endothelial cells and marked accumulation of intravascular blood leukocytes. Fewer leukocytes accumulate in lung than in kidney allografts. Lung transplantion was performed in the Dark Agouti to Lewis rat strain combination. Intravascular and intraalveolar leukocytes were isolated from the grafts, and we evaluated the mRNA expression of NPY, Y1, and Y2 by real-time RT-PCR as well as the peptide expression of NPY by radioimmunoassay and immunohistochemistry. NPY and Y1 were expressed by pulmonary intravascular and intraalveolar leukocytes. Y1 was up-regulated by pulmonary intravascular and intraalveolar leukocytes during allograft rejection while Y2 could not be detected. Higher NPY expression levels in intravascular leukocytes were observed in lung compared to kidney allografts, which were investigated previously. Our findings suggest that an increased leukocytic expression of NPY in lung compared to kidney allografts results in a reduced accumulation of leukocytes in allograft vessels.

A Single 9-Colour Flow Cytometric Method to Characterise Major Leukocyte Populations in the Rat: Validation in a Model of LPS-Induced Pulmonary Inflammation

The rat is a commonly used model for immunological investigation. Yet basic research and characterisation of leukocyte populations and sub-sets lags far behind murine research, with inconsistency on reported leukocyte markers and their overlap. These shortcomings limit the opportunity for more complex and advanced rat immunology research. In this study, we developed a robust 9-colour flow-cytometric protocol to elucidate the major blood and tissue rat leukocyte populations, and validated it in a model of LPS-induced pulmonary inflammation. Blood and tissues (lung, BALF, spleen, liver, bone marrow) from naïve Sprague-Dawley rats were collected and analysed by flow cytometry (FCM). Rats were exposed to aerosolised saline or LPS (1 mg/mL), at 3 and 24 hrs thereafter blood, lung and BALF were collected and analysed using FCM and ELISA. Neutrophils, two monocyte subsets, NK Cells, B Cells, CD4+, CD8+ T Cells and alveolar macrophages can be identified simultaneously across different tissues using a 9-colour panel. Neutrophils and monocytes can be distinguished based upon differential expression of CD43 and His48. Neutrophils and CD43Lo/His48Hi monocyte-macrophages are elevated in the lung at 3 and 24 hrs during LPS-induced pulmonary inflammation. This validated method for leukocyte enumeration will offer a platform for greater consistency in future rat immunology and inflammation research.

The ratio of circulating regulatory T cells (Tregs)/Th17 cells is associated with acute allograft rejection in liver transplantation

CD4⁺CD25⁺FoxP3⁺ regulatory T cells (Tregs) and Th17 cells are known to be involved in the alloreactive responses in organ transplantation, but little is known about the relationship between Tregs and Th17 cells in the context of liver alloresponse. Here, we investigated whether the circulating Tregs/Th17 ratio is associated with acute allograft rejection in liver transplantation. In present study, thirty-eight patients who received liver transplant were enrolled. The patients were divided into two groups: acute allograft rejection group (Gr-AR) (n = 16) and stable allograft liver function group (Gr-SF) (n = 22). The frequencies of circulating Tregs and circulating Th17 cells, as well as Tregs/Th17 ratio were determined using flow cytometry. The association between Tregs/Th17 ratio and acute allograft rejection was then analyzed. Our results showed that the frequency of circulating Tregs was significantly decreased, whereas the frequency of circulating Th17 cells was significantly increased in liver allograft recipients who developed acute rejection. Tregs/Th17 ratio had a negative correlation with liver damage indices and the score of rejection activity index (RAI) after liver transplantation. In addition, the percentages of CTLA-4⁺, HLA-DR⁺, Ki67⁺, and IL-10⁺ Tregs were higher in Gr-SF group than in Gr-AR group. Our results suggested that the ratio of circulating Tregs/Th17 cells is associated with acute allograft rejection, thus the ratio may serve as an alternative marker for the diagnosis of acute rejection.

Effect of the systemic administration of methylprednisolone on the lungs of brain-dead donor rats undergoing pulmonary transplantation

OBJECTIVE

Most lung transplants are obtained from brain-dead donors. The physiopathology of brain death involves hemodynamics, the sympathetic nervous system, and inflammatory mechanisms. Administering methylprednisolone 60 min after inducing brain death in rats has been shown to modulate pulmonary inflammatory activity. Our objective was to evaluate the effects of methylprednisolone on transplanted rat lungs from donors treated 60 min after brain death.

METHODS

Twelve Wistar rats were anesthetized, and brain death was induced. They were randomly divided into two groups (n=6), namely a control group, which was administered saline solution, and a methylprednisolone group, which received the drug 60 min after the induction of brain death. All of the animals were observed and ventilated for 2 h prior to being submitted to lung transplantation. We evaluated the hemodynamic and blood gas parameters, histological score, lung tissue levels of thiobarbituric acid-reactive substances, level of superoxide dismutase, level of tumor necrosis factor-alpha, and level of interleukin-1 beta.

RESULTS

After transplantation, a significant reduction in the levels of tumor necrosis factor-alpha and IL-1β was observed in the group that received methylprednisolone (p=0.0084 and p=0.0155, respectively). There were no significant differences in tumor necrosis factor-alpha and superoxide dismutase levels between the control and methylprednisolone groups (p=0.2644 and p=0.7461, respectively). There were no significant differences in the blood gas parameters, hemodynamics, and histological alterations between the groups.

CONCLUSION

The administration of methylprednisolone after brain death in donor rats reduces inflammatory activity in transplanted lungs but has no influence on parameters related to oxidative stress.

A relevant experimental model for human bronchiolitis obliterans syndrome

BACKGROUND

The long-term success of human lung transplantation is limited by the development of bronchiolitis obliterans syndrome. Acute rejection episodes and infections are important risk factors and seem to play major pathogenic roles. We established a relevant experimental model that mimics important aspects of human bronchiolitis obliterans syndrome.

METHODS

The Fischer 344-to-Lewis rat strain combination was used for orthotopic left lung transplantation. Isogeneic transplantations were performed in the Lewis rat. Recipients were treated with ciclosporin for 10 days. Lipopolysaccharide or vehicle was instilled into the airways 28 days after transplantation. Grafts were monitored by computed tomography, and recipients were euthanized on Days 28-90. The messenger RNA expression of selected chemokines and their receptors was measured on Days 28, 29, 33, 40 after transplantation. Graft histopathology on Day 90 was compared with lungs from patients who underwent re-transplantation due to end-stage allograft dysfunction.

RESULTS

Lung allografts treated with ciclosporin and vehicle only sporadically displayed tissue remodeling. In contrast, lipopolysaccharide treatment induced severe inflammation. In the long-term, severe vascular remodeling, lung fibrosis, and fibroproliferative remodeling of airways were found that closely resemble the histopathologic changes in grafts from human patients with bronchiolitis obliterans syndrome. Chronic damage was virtually absent from pulmonary isografts and native right lungs. Chemokine (C-C motif) ligand 5 and chemokine (C-X-C motif) ligand 9-11, and their receptors, were over-expressed in allografts.

CONCLUSIONS

Our experimental model mirrors key aspects of human bronchiolitis obliterans syndrome. It will be useful to elucidate its pathogenesis and to develop therapeutic approaches improving the long-term outcome of human lung transplantation.

CMV driven CD8(+) T-cell activation is associated with acute rejection in lung transplantation

Lung transplantation is the definitive treatment for terminal respiratory disease, but the associated mortality rate is high. Acute rejection of the transplanted lung is a key determinant of adverse prognosis. Furthermore, an epidemiological relationship has been established between the occurrence of acute lung rejection and cytomegalovirus infection. However, the reasons for this association remain unclear. Here, we performed a longitudinal characterization of CMV-specific T-cell responses and immune activation status in the peripheral blood and bronchoalveolar lavage fluid of forty-four lung transplant patients. Acute rejection was associated with high levels of cellular activation in the periphery, reflecting strong CMV-specific CD8(+) T-cell activity post-transplant. Peripheral and lung CMV-specific CD8(+) T-cell responses were very similar, and related to the presence of CMV in the transplanted organ. These findings support that activated CMV-specific CD8(+) T-cells in the lung may play a role in promoting acute rejection.

1,25-Dihydroxycholecalciferol with low-calcium diet reduces acute rejection in rat lung allotransplantation

OBJECTIVES

The effect of 1,25-dihydroxycholecalciferol (calcitriol, vitamin D3) with a low-calcium diet on the acute lung allograft rejection in a rat unilateral left lung transplantation model was evaluated.

METHODS

Three transplantation groups were studied (n = 5, male Brown-Norway to Fischer F344, 235 ± 15 g body weight): calcitriol and low-calcium diet, low-calcium diet and normal diet. Calcitriol (4 μg/kg/day) was injected intraperitoneally for 5 days, starting from the day of transplantation. In addition, two non-transplantation groups were compared: (n = 3, Brown-Norway) to measure the level of cytokines, and Fischer F344 receiving calcitriol and a low-calcium diet to measure the serum calcium level. The recipients of transplantation were killed on Day 5 post-transplant. The contralateral right main bronchus and the pulmonary artery were occluded for 5 min and blood was drawn for the blood gas analysis, and the grafts were assessed for histology (International Society for Heart and Lung Transplantation 1996/rank scale). Lung levels of interleukin (IL)-2, IL-6, IL-12 and tumour necrosis factor-α (TNF-α) were assessed within the calcitriol and low-calcium diet, low-calcium diet and Brown-Norway groups. The serum calcium level was assessed in the Fischer F344 group. An analysis of variance with Tukey's post hoc test was used to compare the arterial blood oxygen pressure and the lung cytokine expression between groups. A non-parametric Kruskal-Wallis test followed by the Siegel and Castellan post hoc test was used to assess the differences between the groups according to the lung graft rejection grading. Student's paired t-test was used to compare the serum calcium level.

RESULTS

The arterial PaO(2) was significantly higher in the calcitriol and the low-calcium diet groups when compared with low-calcium diet or normal diet groups (356 ± 72 mmHg; P < 0.05 vs other groups). The arterial and bronchial rejection observed in calcitriol and low-calcium diet group was significantly milder than in the low-calcium diet or normal diet groups (A1-2, B1-2; P < 0.05 vs other groups). IL-2 and IL-6 levels were significantly higher in low-calcium diet vs calcitriol and low-calcium diet and Brown-Norway groups. IL-12 and TNF-α did not differ among the groups. There was no significant difference in serum calcium level before and after the treatment in the Fischer F344 group.

CONCLUSIONS

Calcitriol with a low-calcium diet treatment improves lung function, reduces lung allograft acute rejection, decreases IL-2 and IL-6 allograft expression and does not change the serum calcium level significantly.

Prostaglandin E2 as an inhibitory modulator of fibrogenesis in human lung allografts

RATIONALE

Donor mesenchymal stromal/stem cell (MSC) expansion and fibrotic differentiation is associated with development of bronchiolitis obliterans syndrome (BOS) in human lung allografts. However, the regulators of fibrotic differentiation of these resident mesenchymal cells are not well understood.

OBJECTIVES

This study examines the role of endogenous and exogenous prostaglandin (PG)E2 as a modulator of fibrotic differentiation of human lung allograft-derived MSCs.

METHODS

Effect of PGE2 on proliferation, collagen secretion, and α-smooth muscle actin (α-SMA) expression was assessed in lung-resident MSCs (LR-MSCs) derived from patients with and without BOS. The response pathway involved was elucidated by use of specific agonists and antagonists.

MEASUREMENT AND MAIN RESULTS

PGE2 treatment of LR-MSCs derived from normal lung allografts significantly inhibited their proliferation, collagen secretion, and α-SMA expression. On the basis of pharmacologic and small-interfering RNA approaches, a PGE2/E prostanoid (EP)2/adenylate cyclase pathway was implicated in these suppressive effects. Stimulation of endogenous PGE2 secretion by IL-1β was associated with amelioration of their myofibroblast differentiation in vitro, whereas its inhibition by indomethacin augmented α-SMA expression. LR-MSCs from patients with BOS secreted significantly less PGE2 than non-BOS LR-MSCs. Furthermore, BOS LR-MSCs were found to be defective in their ability to induce cyclooxygenase-2, and therefore unable to up-regulate PGE2 synthesis in response to IL-1β. BOS LR-MSCs also demonstrated resistance to the inhibitory actions of PGE2 in association with a reduction in the EP2/EP1 ratio.

CONCLUSIONS

These data identify the PGE2 axis as an important autocrine-paracrine brake on fibrotic differentiation of LR-MSCs, a failure of which is associated with BOS.

Proliferation of CD8-positive T cells in blood vessels of rat renal allografts

It is still disputed in which anatomical compartments of allograft recipients T-cells proliferate. After experimental renal transplantation, host monocytes and lymphocytes accumulate in the lumina of graft blood vessels. In this study, we test the hypothesis that T lymphocytes proliferate in the vascular bed of the graft. Kidneys were transplanted in the Dark Agouti to Lewis rat strain combination, an established experimental model for acute rejection. Isogeneic transplantation was performed as a control. Cells in the S-phase of mitosis were detected in situ three days posttransplantation by pulse-labeling with BrdU and by immunohistochemical detection of the proliferating cell nuclear antigen (PCNA). More than 20% of all T-cells in the lumina of allograft blood vessels incorporated BrdU and approximately 30% of them expressed PCNA. In the blood vessels of isografts as well as in other organs of allograft recipients, only few BrdU(+) cells were detected. A majority of the BrdU(+) cells in graft blood vessels expressed CD8. In conclusion, we demonstrate that CD8(+) T lymphocytes proliferate in the lumina of the blood vessels of renal allografts during the onset of acute rejection.

Leukocyte accumulation in graft blood vessels during self-limiting acute rejection of rat kidneys

During self-limiting acute rejection preceding chronic vasculopathy, large amounts of leukocytes, predominantly monocytes, interact with the endothelium of renal allografts. We aim to characterize them and to identify targets for functional and interventional studies. Leukocytes were harvested by vascular perfusion from Fischer 344 to Lewis renal allografts or Lewis isografts, followed by flow cytometry, quantitative RT-PCR and genome-wide transcriptional profiling. Leukocyte accumulation peaked in allografts on day 9. The percentage of monocytes expressing MHC class II and CD161 was increased whereas CD4, CD11a, CD43, and CD71 expression remained unchanged. IFN-γ, IL-1β, IL-2, IL-10, TNF-α, and iNOS mRNA increased in allograft leukocytes but IL-4, IL-6, IL-12, TGF-β, and tissue factor did not. During acute rejection, 1783 genes were differentially expressed. In conclusion, graft blood leukocytes display a unique state of partial activation during self-limiting rejection. Numerous differentially expressed genes deserve further investigation as potential factors in deciding the fate of the allograft.

"To B or not to B?" B-cells and graft rejection

There is increasing evidence that various maturational stages of B-cells infiltrate various solid organ transplants undergoing acute rejection. The presence of immature CD20 and mature CD138 plasma cells associate with more aggressive and steroid-recalcitrant graft rejection and portend poor graft outcomes. Though associative, the causal role of B-cells in graft rejection remains to be better understood. This review discusses the possible roles of B-cells in graft rejection, whether involved as antigen presenting, as indirect effector, or antibody producing cells.