Role of the eosinophil in chronic vascular rejection of renal allografts

Solving the Conundrum of Eosinophils in Alloimmunity

Eosinophils are bone-marrow-derived granulocytes known for their ability to facilitate clearance of parasitic infections and their association with asthma and other inflammatory diseases. The purpose of this review is to discuss the currently available human observational and animal experimental data linking eosinophils to the immunologic response in solid organ transplantation. First, we present observational human studies that demonstrate a link between transplantation and eosinophils yet were unable to define the exact role of this cell population. Next, we describe published experimental models and demonstrate a defined mechanistic role of eosinophils in downregulating the alloimmune response to murine lung transplants. The overall summary of this data suggests that further studies are needed to define the role of eosinophils in multiple solid organ allografts and points to the possibility of manipulating this cell population to improve graft survival.

Large Multinucleated Variant Endothelial Cells (MVECs) in Allograft Kidney Microvasculature: A Biopsy Series

There are few published studies examining cytomorphologic alterations in endothelial cells in human tissue. One fascinating but largely unexplored endothelial morphologic variant is large multinucleated variant endothelial cells (MVECs). To our knowledge, there are no published reports of MVECs identified in the kidney. Here, we present a case series of 4 kidney biopsies from allograft kidneys whose microvasculature contained MVECs. Electron microscopy confirmed the endothelial identity in all cases. A broad immunohistochemical panel used in 1 case was also confirmatory of an endothelial cell origin. All cases occurred in the setting of chronic, active, antibody-mediated rejection, and alternative etiologies, such as viral infections, were excluded. Two patients were positive for concurrent donor-specific antibodies, and 3 of the 4 cases occurred in second kidney allografts. We speculate that MVECs are a rare or often overlooked finding often confused for megakaryocytes and may be associated with chronic endothelial cell injury in the setting of chronic antibody-mediated rejection.

Deciphering the role of eosinophils in solid organ transplantation

Eosinophils are rare granulocytes that belong to the innate arm of the immune system. This cell population is traditionally defined as a destructive and cytotoxic mediator in asthma and helminth infection. Limited data in transplantation have suggested that eosinophils play a similar role in potentiating deleterious organ inflammation and immunologic rejection. Contrary to this long-held notion, recent data have uncovered the possibility that eosinophils play an alternative role in immune homeostasis, defense against a wide range of pathogens, as well as downregulation of deleterious inflammation. Specifically, translational data from small animal models of lung transplantation have demonstrated a critical role for eosinophils in the downregulation of alloimmunity. These findings shed new light on the unique immunologic features of the lung allograft and demonstrate that environmental polarization may alter the phenotype and function of leukocyte populations previously thought to be static in nature. In this review, we provide an update on eosinophils in the homeostasis of the lung as well as other solid organs.

Early Eosinophilic Antibody-mediated Rejection in a Renal Allograft Recipient

Although the predominant component of acute allograft rejection is the T-cells, the milieu is not devoid of other inflammatory cells including plasma cells, eosinophils, and histiocytes. Apart from the CD8 T cell and CD4 T cell-FasL cytotoxicity, experimental models had proven a pivotal role of Th-2 cells in acute rejection, and these have been associated with marked tissue eosinophilia. Herein, we present a unique case of severe eosinophilic acute antibody-mediated rejection in a 22 years old deceased donor renal allograft recipient, within 4 days of transplantation without peripheral eosinophilia. The pathology was successfully dealt with the prevailing modalities of therapy, including steroids, plasmapheresis, intravenous immunoglobulin, and bortezomib. Concurrently, we have briefly reviewed the literature about the role of eosinophils in graft rejection and its prognostication.

A Player and Coordinator: The Versatile Roles of Eosinophils in the Immune System

Eosinophils have traditionally been associated with allergic diseases and parasite infection. Research advances in the recent decades have brought evolutionary changes in our understanding of eosinophil biology and its roles in immunity. It is currently recognized that eosinophils play multiple roles in both innate and adaptive immunity. As effector cells in innate immunity, eosinophils exert a pro-inflammatory and destructive role in the Th2 immune response associated with allergic inflammation or parasite infection. Eosinophils can also be recruited by danger signals released by pathogen infections or tissue injury, inducing host defense against parasitic, fungal, bacterial or viral infection or promoting tissue repair and remodeling. Eosinophils also serve as nonprofessional antigen-presenting cells in response to allergen challenge or helminth infection, and, meanwhile, are known to function as a versatile coordinator that actively regulates or interacts with various immune cells including T lymphocytes and dendritic cells. More roles of eosinophils implicated in immunity have been proposed including in immune homeostasis, allograft rejection, and anti-tumor immunity. Eosinophil interactions with structural cells are also implicated in the mechanisms in allergic inflammation and in Helicobacter pylori gastritis. These multifaceted roles of eosinophils as both players and coordinators in immune system are discussed in this review.

Allo-reactivity of mesenchymal stem cells in rhesus macaques is dose and haplotype dependent and limits durable cell engraftment in vivo

The emerging paradigm that MSCs are immune privileged has fostered the use of “off-the-shelf” allogeneic MSC-based therapies in human clinical trials. However, this approach ignores studies in experimental animals wherein transplantation of MSCs across MHC boundaries elicits measurable allo-immune responses. To determine if MSCs are hypo-immunogeneic, we characterized the immune response in rhesus macaques following intracranial administration of allogeneic vs. autologous MSCs. This analysis revealed unambiguous evidence of productive allo-recognition based on expansion of NK, B and T cell subsets in peripheral blood and detection of allo-specific antibodies in animals administered allogeneic but not autologous MSCs. Moreover, the degree of MHC class I and II mismatch between the MSC donor and recipient significantly influenced the magnitude and nature of the allo-immune response. Consistent with these findings, real-time PCR analysis of brain tissue from female recipients administered varying doses of male, allogeneic MSCs revealed a significant inverse correlation between MSC engraftment levels and cell dose. Changes in post-transplant neutrophil and lymphocyte counts also correlated with dose and were predictive of overall MSC engraftment levels. However, secondary antigen challenge failed to elicit a measurable immune response in allogeneic recipients. Finally, extensive behavior testing of animals revealed no main effect of cell dose on motor skills, social development, or temperament. Collectively, these data indicate that allogeneic MSCs are weakly immunogenic when transplanted across MHC boundaries in rhesus macaques and this negatively impacts durable engraftment levels. Therefore the use of unrelated donor MSCs should be carefully evaluated in human patients.

Sclerosing peritonitis, a rare complication after intestinal transplant. Report of one case successfully treated with adjustment of immunosuppression

Sclerosing peritonitis is a complication described in different clinical situations, such as patients that underwent prolonged peritoneal dialysis or renal transplantation with previous history of peritoneal dialysis. The origin of this entity is unclear so far and it is believed that several mechanisms may contribute to its development. The hallmark of sclerosing peritonitis is the continuous accumulation of fibrocollagenous deposits in the intestinal wall and mesenteries causing progressive adhesion of the intestinal loops and mesenteric retraction resulting in intestinal obstruction. Also, it has been described as a rare complication after intestinal transplant that might lead to graft failure. In this report, we describe a case of sclerosing peritonitis after intestinal transplantation that was successfully treated with modifications in the immunosuppressive regime allowing restitution of gastrointestinal transit and intestinal autonomy.

TGF-β1 Expression in Renal Allograft Rejection and Cyclosporine A Toxicity

BACKGROUND

To assess short- and long-term influence of the TGF-beta1 on renal allografts.

METHODS

Expression of TGF-beta1 and TNF-alpha, and the proportion of macrophages and eosinophils in interstitium were evaluated in 64 cases including five cases with nonrejected kidneys (NRK), 18 cases with acute rejection (AR), 26 cases with chronic allograft nephropathy (CAN), and 15 cases with acute cyclosporine A (CsA) toxicity. Follow-up biopsies of all cases with AR and CsA toxicity were evaluated for development of interstitial fibrosis (IF) and graft atherosclerosis (GAS). Additionally, influence of tubular-TGF-beta1 expression on graft function during 6 months after the diagnostic biopsy was evaluated.

RESULTS

A significant differences was seen between rejected kidneys and acute CsA toxicity in regards of tubular TGF-beta1 expression that patients with CsA toxicity exhibited significantly higher grade of tubular TGF-beta1 expression than patients with AR (P<0.05) and CAN (P<0.05). A significant difference was found between the grades of tubular TGF-beta1 expression in regards to graft function of cases with AR and CsA toxicity (P<0.05). Higher grade tubular TGF-beta1 expression showed better graft function during 6 months. Besides the degree of renal TGF-beta1 expression was positively correlated with development of diffuse IF and GAS (P<0.05) that the risk of the IF and GAS was higher in cases with grade 2 renal TGF-beta1 expression.

CONCLUSIONS

Despite the short-term posttransplantation tubule-repairing effects of TGF-beta1, the overall effects of TGF-beta1 in the kidney seem to be negative that increased expression of TGF-beta1 promotes IF and vasculopathy associated with CAN.

Neointimal Inflammation and Adventitial Angiogenesis Correlate With Severity of Cardiac Allograft Vasculopathy in Pediatric Recipients

BACKGROUND

Chronic inflammation and angiogenesis have been implicated in the pathogenesis of both cardiac allograft vasculopathy (CAV) and age-related vasculopathy. Because concurrent atherosclerosis does not complicate assessment of CAV in children, we sought to characterize the spectrum of coronary lesions in this population and determine whether inflammatory infiltrates and angiogenesis correlate with severity of CAV.

METHODS

In 18 pediatric heart specimens CAV was graded 1 to 4 (none to severe). Each case was assigned to either: Group I, no inflammation; Group II, perivascular inflammation; or Group III, perivascular and neointimal inflammation. Inflammatory infiltrates were immunophenotyped using anti-CD3, anti-CD20 and HAM 56. Angiogenesis was assessed by determining microvascular density (MVD) in 5 high-power fields (HPFs) per section.

RESULTS

CAV was evident in 94% of cases, and inflammation in 61%. Cases with neointimal inflammation had significantly more severe CAV compared with cases without inflammation (2.7 +/- 0.16 vs 1.9 +/- 0.2, p = 0.002). MVD was significantly higher in both inflammation groups (Groups II and III) compared with Group I (4.1 +/- 0.5 per HPF and 5.9 +/- 0.5 vs 3.1 +/- 0.7, p = 0.018 and p = 0.002) and correlated with the degree of CAV (p = 0.007). The perivascular infiltrates (Group II, n = 5) contained lymphocytes, macrophages and plasma cells, and 67% of neointimal infiltrates (Group III, n = 6) also contained eosinophils.

CONCLUSIONS

CAV in children is more common than previously reported. Our data indicate that CAV is often associated with inflammation and that adventitial angiogenesis correlated with the severity of CAV.

Abundance of interstitial eosinophils in renal allografts is associated with vascular rejection

BACKGROUND

The authors investigated the possible relevance of significant interstitial graft eosinophilic infiltrate (SIGEI) to the pathologic diagnosis of renal transplants.

METHODS

The authors performed a clinical and pathologic review of 29 consecutive patients with renal allograft failure and nephrectomy. As a result of their size, such specimens are more conducive than biopsies to the investigation of large blood vessels. SIGEI was diagnosed when eosinophils represented 10% or more of the interstitial inflammatory infiltrate. Vascular rejection was graded according to the Banff criteria. Risk for allergic interstitial nephritis and immunosuppression at the time of the nephrectomy-high dose, minimal, or none-was determined from the clinical history.

RESULTS

SIGEI was observed in 13 of the 29 patients and was absent in 16. Vascular (Banff type II) rejection was present in 11 of 13 cases with SIGEI and in 9 of 16 cases without SIGEI. The relation between SIGEI and Banff type II rejection was statistically significant: in 14 patients on high-dose immunosuppression, vascular rejection was present in all 5 cases with SIGEI, whereas in the 9 grafts without SIGEI, only 3 had vascular rejection (P=0.04). The authors did not find an association between SIGEI and risk for iatrogenic interstitial nephritis: SIGEI was seen in only 4 of 15 patients with high or moderate iatrogenic risk.

CONCLUSIONS

In this series of allograft nephrectomies, SIGEI was significantly associated with vascular rejection (Banff type II) but not with risk of allergic iatrogenic nephritis, suggesting that the presence of SIGEI may be a helpful criterion in the pathologic diagnosis of renal allografts.

FTY720, an immunosuppressant that alters lymphocyte trafficking, abrogates chronic rejection in combination with cyclosporine A

BACKGROUND

Chronic rejection remains the leading cause of failure after transplantation (Tx). FTY720, a new immunosuppressant altering lymphocyte trafficking, is effective against acute rejection, but its activity against chronic rejection is not known.

METHODS

A valid model of chronic rejection was produced. Heart transplantation (HTx) was performed using fully mismatched RA (RT1p) and PVG (RT1c) rats. Administration of donor-specific blood transfusion 12 days before HTx prolongs graft survival, but features of chronic rejection including intimal hyperplasia and vascular obliteration (VO) develop with time only in allogeneic Tx. This is therefore a valid model of chronic rejection. VO was assessed on post-Tx day 90 in six groups differing according to the maintenance immunosuppressive regimen administered. group 1, donor-specific blood transfusion only and no other treatment; group 2, FTY720 (0.3 mg/kg/day orally) for 90 days; group 3, cyclosporine A (CsA) (1 mg/kg/day orally) for 90 days; group 4, combined administration of FTY720 and CsA for 90 days; group 5, transient administration of combined FTY720 and CsA for 7 days; and group 6, syngeneic HTx (RA to RA). Graft infiltrate, endothelial immunoglobulin (Ig) G deposition, and complement binding were also examined on post-Tx day 90.

RESULTS

In control group 1, severe VO was observed, compared with syngeneic HTx (group 6). Monotherapy with FTY720 (group 2) or with CsA (group 3) significantly but partially reduced VO. On the contrary, combined administration of FTY720 and CsA (group 4) abrogated VO. A 1-week treatment with combined FTY720 and CsA (group 5) reduced VO but only partially. In group 1, arteriosclerosis was accompanied by graft infiltrate, endothelial IgG deposition, and complement binding. In groups 2, 3, and 5, graft infiltrating scores were partially decreased compared with group 1 but remained higher than in syngeneic controls; endothelial IgG deposition and complement binding were still present. In group 4, continuous administration of combined FTY720 and CsA reduced graft infiltrate to the level of syngeneic control and abrogated both endothelial IgG deposition and complement binding.

CONCLUSIONS

Maintenance treatment with either FTY720 or CsA monotherapy partially prevents chronic rejection; short-term treatment with combined FTY720 and CsA reduces chronic rejection only partially; and continuous treatment with combined FTY720 and CsA abrogates chronic rejection, and this is accompanied by dramatic reduction of graft infiltrating cells, endothelial IgG deposition, and complement binding. Prevention of chronic rejection by maintenance treatment with FTY720 and CsA represents indirect evidence that normal lymphocyte trafficking and function are mandatory for development of chronic rejection.

Non-classical pathways of cell-mediated allograft rejection: new challenges for tolerance induction?

Allograft rejection results from separate pathways primarily controlled by CD4+ T cells. Refinement of transplantation models together with investigations on rejection occurring despite co-stimulation blockade revealed unexpected pathways involving CD8+ T cells, NK cells and Th2 cytokines. In this minireview, we discuss these non-classical pathways of allograft rejection and their relevance for the induction of tolerance in the clinics.

Proliferative effects of eosinophil lysates on cultured human airway smooth muscle cells

BACKGROUND

The hypertrophy/hyperplasia of airway smooth muscle (ASM) cells is one of the characteristic features of bronchial asthma. This structural change leads to the thickening of airway walls resulting in the amplification of airway narrowing. However, the pathogenesis of this structural change has not yet been determined. Eosinophils, which play a pathogenic role in asthma, have been demonstrated to have proliferative effects on fibroblasts and vascular smooth muscle cells.

OBJECTIVE

We attempted to investigate the potential of eosinophils to induce the proliferation of ASM cells.

METHODS

We examined the effect of lysates of eosinophils purified from peripheral blood of healthy donors on cultured human ASM cell proliferation.

RESULTS

Eosinophil lysates significantly induced ASM cell proliferation in time- and dose-dependent manners, reaching a maximum on day 6 at 50% of eosinophil lysates (6.0 +/- 0.7 x 104 [mean +/- SD] /well, n = 5 vs. 4.5 +/- 1.1 x 104/well, n = 5; P < 0.05). This proliferative activity was heat-sensitive and recovered in the soluble fraction of the eosinophil lysates. Furthermore, the molecular weight of the mitogenic activity in the soluble fraction was identified as lower than 10 kDa. The inhibitory activity to ASM cell proliferation was also found in the insoluble fraction of the lysates.

CONCLUSION

These results indicate that circulating eosinophils store mitogenic activity for ASM cells, suggesting that eosinophils might contribute to the development of the hyperplasia of ASM cells in asthmatics through the release of the stored mitogenic activity upon stimulation at the site of inflammation.

Critical role for IL-4 in the development of transplant arteriosclerosis in the absence of CD40-CD154 costimulation

Blockade of the CD40-CD154 pathway can inhibit CD4(+) T cell activation but is unable to prevent immune responses mediated by CD8(+) T cells. However, even in the absence of CD8(+) T cells, inhibition of the CD40-CD154 pathway is insufficient to prevent the development of transplant arteriosclerosis. This study investigated the mechanisms of transplant arteriosclerosis in the absence of the CD40 pathway. C57BL/6 CD40(-/-) (H2(b)) recipients were transplanted with MHC-mismatched BALB/c (H2(d)) aortas. Transplant arteriosclerosis was evident in both CD40(-/-) and CD40(+/-) mice (intimal proliferation was 59 +/- 5% for CD40(-/-) mice vs 58 +/- 4% for CD40(+/-) mice) in the presence or absence of CD8(+) T cells (intimal proliferation was 46 +/- 7% for CD40(-/-) anti-CD8-treated mice vs 50 +/- 10% for CD40(+/-) anti-CD8-treated mice), confirming that CD8(+) T cells are not essential effector cells for the development of this disease. In CD40(-/-) recipients depleted of CD8(+) T cells, the number of eosinophils infiltrating the graft was markedly increased (109 +/- 24 eosinophils/grid for CD40(-/-) anti-CD8-treated mice vs 28 +/- 7 for CD40(+/-) anti-CD8-treated mice). The increased presence of eosinophils correlated with augmented intragraft production of IL-4. To test the hypothesis that IL-4 was responsible for the intimal proliferation, CD8 T cell-depleted CD40(-/-) recipients were treated with anti-IL-4 mAb. This resulted in significantly reduced eosinophil infiltration into the graft (12 +/- 5 eosinophils/grid for CD40(-/-) anti-CD8(+), anti-IL-4-treated mice vs 109 +/- 24 for CD40(-/-) anti-CD8-treated mice), intragraft eotaxin, CCR3 mRNA production, and the level of intimal proliferation (18 +/- 5% for CD40(-/-) anti-CD8(+)-, anti-IL-4-treated mice vs 46 +/- 7% for CD40(-/-) anti-CD8-treated mice). In conclusion, elevated intragraft IL-4 production results in an eosinophil infiltrate and is an important mechanism for CD8(+) T cell-independent transplant arteriosclerosis in the absence of CD40-CD154 costimulation.

Eosinophilic infiltrates in a pulmonary allograft: a case and review of the literature

An unusual case of peribronchial eosinophilic infiltrates associated with peripheral blood eosinophilia in a lung transplant patient is described. The role that eosinophils play in lung allograft rejection is reviewed. Tissue eosinophils have been associated with acute pulmonary allograft rejection. Although, eosinophils in bronchoalveolar lavage fluid (BAL) have been observed in allograft rejection, this relationship is less well defined. The role of eosinophils in the pathophysiology of allograft rejection is unclear.

A role for eosinophils in transplant rejection

Eosinophils release inflammatory mediators and cationic proteins that are instrumental in the pathogenesis of allergic diseases such as bronchial asthma. Here, we review experimental observations indicating that eosinophils are also involved in the rejection of allografts. We propose that their role as effectors of transplant damage becomes crucial when classical pathways of rejection are inhibited and T helper 2 (Th2) cells dominate the alloimmune response.

IL-5 Mediates Eosinophilic Rejection of MHC Class II-Disparate Skin Allografts in Mice

CD4 T cells play a crucial role in the acute rejection of MHC class II-disparate skin allografts, mainly by Fas/Fas ligand-mediated cytotoxicity. Because recent observations indicate that eosinophils may be found within allografts rejected by CD4 T cells, we evaluated the role played by IL-5, the main eosinophil growth factor, and by eosinophils in the rejection of MHC class II-disparate skin grafts. C57BL/6 mice rapidly rejected MHC class II-disparate bm12 skin grafts. Rejected skins contained a dense, aggressive eosinophil infiltrate. Lymphocytes isolated from lymph nodes draining rejected bm12 skin were primed for IL-5 secretion, and IL-5 mRNA was present within rejected grafts. The IL-5/eosinophil pathway played an effector role in allograft destruction, because the rejection of bm12 skin was significantly delayed in IL-5-deficient mice as compared with wild-type animals. The role of the IL-5/eosinophil pathway was further investigated in MHC class II-disparate donor-recipient strains unable to establish Fas/Fas ligand interactions. Fas ligand-deficient gld/gld mice rejected bm12 skins, and bm12 mice rejected Fas-deficient lpr/lpr C57BL/6 skins. Neutralization of IL-5 prevented acute rejection in both combinations. We conclude that MHC class II-disparate skin allografts trigger an IL-5-dependent infiltration of eosinophils that is sufficient to result in acute graft destruction.

Critical roles for IL-4, IL-5, and eosinophils in chronic skin allograft rejection

C57BL/6 mice injected with the 145-2C11 anti-CD3 mAb and grafted with MHC class II disparate bm12 skin develop a chronic rejection characterized by interstitial dermal fibrosis, a marked eosinophil infiltrate, and an obliterative intimal vasculopathy. Because these changes occur in the absence of alloreactive antibodies, we examined the contribution of cytokines in their pathogenesis. Chronically rejected grafts showed a marked accumulation of both IL-4 and IL-5 mRNA. Mixed lymphocyte reaction experiments established that mice undergoing chronic rejection were primed for IL-4, IL-5, and IL-10 secretion. In vivo administration of anti-IL-4 mAb completely prevented allograft vasculopathy as well as graft eosinophil infiltration and dermal fibrosis. Injection of anti-IL-5 mAb or the use of IL-5-deficient mice as recipients also resulted in the lack of eosinophil infiltration or dermal fibrosis, but these mice did develop allograft vasculopathy. Administration of anti-IL-10 mAb did not influence any histologic parameter of chronic rejection. Thus, in this model, IL-4- and IL-5-mediated tissue allograft eosinophil infiltration is associated with interstitial fibrosis. IL-4, but not eosinophils, is also required for the development of obliterative graft arteriolopathy.

Chronic rejection of major histocompatibility complex class II-disparate skin grafts after anti-CD3 therapy: a model of antibody-independent transplant vasculopathy

BACKGROUND

Chronic rejection remains a leading cause of allograft loss. Histologically, it is characterized by arterial intimal thickening and parenchymal fibrosis. The immune mechanisms triggering chronic rejection are still uncompletely understood.

METHODS

We performed major histocompatibility complex (MHC) class H-incompatible skin grafts from C-H2bm12 (bm12, H2bm12) into C57BL/6 (C57BL/6, H2b) recipients immunosuppressed with a short course of anti-CD3 monoclonal antibodies to prevent acute rejection.

RESULTS

More than 80% of grafts survived for prolonged periods, but eventually all displayed macroscopic and microscopic evidence of chronic rejection. At histology, there was a progressive arterial intimal thickening as well as intense dermal fibrosis. This was accompanied by an inflammatory infiltrate consisting of lymphocytes and macrophages, but also of a considerable number of eosinophils. Mice with chronic rejection were unable to generate anti-donor MHC class II cytotoxic T lymphocyte activity at either 20 or 60 days after transplant. Furthermore, transplantation of bm12 skins on C57BL/6-congenic, Ig knock-out mice was associated with the development of a chronic rejection that was identical to that occurring in wild-type C57BL/6 animals, indicating that alloantibodies are not necessary in this model.

CONCLUSIONS

(1) Skin grafts may undergo chronic rejection with the characteristic lesions of vasculopathy and fibrosis; (2) chronic rejection of MHC class II-disparate skins may occur in the absence of direct cytotoxic T lymphocyte activity or alloantibodies.

Eosinophils in acute cellular rejection in liver allografts

Eosinophils have a role in various allergic and inflammatory disease processes and participate in the process of acute rejection in solid organ allografts. Initial studies described the diagnostic value of eosinophils in kidney allograft rejection. Graft eosinophilia is a sensitive and specific marker of acute rejection in liver allografts and has been incorporated as one of the diagnostic criteria of acute rejection by the Royal Free Hospital scoring system. Blood eosinophilia also has been investigated and is a useful diagnostic marker of acute rejection in liver and kidney allografts, although studies differ in defining the day of onset of eosinophilia in relation to rejection. Eosinophils probably act through the chemokines interleukin-5 and RANTES (regulated on activation, normal T cells expressed and secreted) in the pathogenesis of acute rejection. Basic cytotoxic proteins, such as eosinophil cationic protein and major basic protein, are released by the eosinophils, and their effector role in acute rejection has been studied through the use of specific monoclonal antibodies. Successful treatment of acute rejection with corticosteroids has been associated with a decrease in graft and blood eosinophil counts. Eosinophils also act as prognostic markers of acute rejection, as shown by studies reporting that patients with elevated eosinophil counts and steroid-resistant rejection showed a worse prognosis. Further research into the effector mechanisms of eosinophils in acute rejection needs to be performed. The ability of eosinophils to distinguish those diseases with different responses to standard immunosuppression and other diseases in the context of acute rejection also needs to be studied.

Eotaxin and capping protein in experimental vasculopathy

Ischemia-induced tissue activation may contribute to the pathogenesis of graft vasculopathy, but the mediators implicated have only partially been characterized. To gain further insight into the molecular mechanisms involved, syngeneic rat aortic transplants with cold-storage-induced vasculopathy were studied for differentially expressed mRNA transcripts. Vessel segments were exposed to either 1 or 18 hours of cold ischemia, followed by transplantation into syngeneic recipients. After 3 days or 4 weeks, the grafts were removed and total mRNA was isolated and used for differential display to identify modulation of transcript expression related to prolonged storage. Using 15 sets of random primers, 17 polymerase chain reaction products were up-regulated and 2 were downregulated in grafts exposed to 18 hours of ischemia. Sequencing of these amplicons showed that 6 had a high degree of homology to known sequences whereas 13 had no homology to any of the genes in the database. Two of the differentially displayed amplicons (capping protein and eotaxin) were cloned, re-amplified, and used as probes for Northern blot analysis to confirm their differential expression. Immunohistochemistry using monoclonal antibodies against capping protein-alpha and eotaxin confirmed that both proteins are expressed in the media of normal aortas and that there was an increased expression in vessels exposed to prolonged ischemia albeit that the increase at the protein level seemed less compared with changes in transcript expression. Northern blots with RNA from aortic allografts exposed to prolonged ischemic storage also showed increased levels of capping protein and eotaxin mRNA whereas there was a decrease in the relative amount of these transcripts in vessels exposed to balloon denudation, suggesting that the increase after prolonged ischemic exposure is not the result of a nonspecific response to injury. Based on the biological characteristics of capping protein and eotaxin it is conceivable that they play a pathogenetic role in ischemia-induced vessel wall remodeling. It remains to be established whether these genes or their products serve as target molecules for therapeutic interventions to prevent or treat cold-storage-induced graft vasculopathy.

Activation of eosinophils in the airways of lung transplantation patients

Eosinophils are important inflammatory cells involved in liver and renal allograft rejection. The role of these cells is less well defined in lung allograft rejection. Eosinophils may be activated in lung rejection and release cytotoxic eosinophil cationic protein (ECP). Other states of disease in lung transplant recipients, such as cytomegalovirus (CMV) and bacterial infection, may also be associated with activated eosinophils. We postulated that ECP may be detectable and elevated in the airway lavage samples obtained from lung transplant patients and may contribute to disease pathogenesis.

METHODS

Fifty BAL samples were collected from 38 lung transplant patients. Their most recent pulmonary function test results within 1 week of collection were noted. The samples were analyzed for the concentration of ECP, WBC count and differential cell count, and total protein level. The results were analyzed to identify the presence of disease or abnormal lung function associated with a positive ECP test. Student's t test was used and a p value of <0.05 was considered significant.

RESULTS

We found that ECP levels were elevated in 36% (n=14) of the patients. Those patients with a positive test result were more likely to have acute rejection, CMV disease, or the presence of a cultured pathogen in BAL compared to patients with a negative test result (p<0.01).

CONCLUSIONS

The presence of BAL ECP is associated with disease in lung transplant patients. Since ECP is directly cytotoxic, it may contribute to disease pathogenesis.