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Biomedical subjects

A Naji

Publications and source records attributed to A Naji.

At least 37 records · Page 2Linked to original sources
PubMed1999

Tracking alloreactive cell division in vivo.

BACKGROUND: The study of alloimmune responses has been limited by a lack of assays that can track the behavior of alloreactive lymphocytes in vivo. Here we utilize an experimental system that allows the identification and study of alloreactive CD4+ lymphocytes responding to major histocompatibility antigens in vivo. METHODS: Responder mouse lymphocytes were labeled with a fluorescein-based dye, adoptively transferred into irradiated allogeneic stimulator mice, and recovered at serial time points for analysis by flow cytometry. RESULTS: Discrete generations of CD4+ responder lymphocytes proliferating specifically in response to allogeneic MHC class II were distinguished by fluorescein intensity. Successive division of alloreactive CD4+ lymphocytes was traced up to six generations after 60 hr. CONCLUSIONS: This experimental system provides information on the division kinetics of alloreactive CD4+ cells. Other applications include immunophenotyping of alloreactive lymphocyte subsets. Further study of systems such as this will allow the detailed characterization of how alloimmune responses are initiated and proceed in vivo.

Animals↗
PubMed1999

Origin, kinetics, and function of chimeric B lymphocytes in liver allografts.

BACKGROUND: Despite the well-recognized concordance of chimerism with spontaneous acceptance of rat liver allografts, the active role and the identity of chimeric cells mediating liver allograft tolerance are unknown. Because resting B cells are endowed with a tolerogenic antigen-presenting capacity, we assessed whether donor B cells propagated from the grafted liver may be responsible for liver allograft tolerance. METHODS: Dark Agouti or Lewis rats were grafted with Lewis or Dark Agouti livers as a tolerogenic or a rejection combination, respectively. We followed the kinetics of donor B cells in recipients by flow cytometry, and we examined the fate of liver allografts depleted of passenger B cells in either B cell-sufficient or -deficient recipients. B-cell depletion was achieved by treatment of animals with polyclonal goat anti-rat IgM antibody from birth. RESULTS: During the first 3 days after liver allografting, donor B cells rapidly migrated from graft-infiltrating cells and appeared in systemic circulation in both the tolerogenic and rejection combinations. However, systemic chimerism was detectable in the tolerogenic combination by day 14, whereas it was undetectable in the rejection combination by day 7. In graft-infiltrating cells, a significant expansion of chimeric IgM+ (newly formed) B cells was observed on day 5 in the tolerogenic, but not in the rejection, combination. However, depletion of B cells from liver grafts and the absence of antibodies failed to alter the outcome of liver allograft survival in the tolerogenic or immunogenic combination. CONCLUSION: Although intragraft chimeric B cells proliferated in tolerogenic liver allografts, their clonal expansion does not seem to be essential for the promotion of liver allograft tolerance.

Animals↗
PubMed1999

I-Ag7-mediated antigen presentation by B lymphocytes is critical in overcoming a checkpoint in T cell tolerance to islet beta cells of nonobese diabetic mice.

B cell-deficient nonobese diabetic (NOD) mice are protected from the development of spontaneous autoimmune diabetes, suggesting a requisite role for Ag presentation by B lymphocytes for the activation of a diabetogenic T cell repertoire. This study specifically examines the importance of B cell-mediated MHC class II Ag presentation as a regulator of peripheral T cell tolerance to islet beta cells. We describe the construction of NOD mice with an I-Ag7 deficiency confined to the B cell compartment. Analysis of these mice, termed NOD BCIID, revealed the presence of functionally competent non-B cell APCs (macrophages/dendritic cells) with normal I-Ag7 expression and capable of activating Ag-reactive T cells. In addition, the secondary lymphoid organs of these mice harbored phenotypically normal CD4+ and CD8+ T cell compartments. Interestingly, whereas control NOD mice harboring I-Ag7-sufficient B cells developed diabetes spontaneously, NOD BCIID mice were resistant to the development of autoimmune diabetes. Despite their diabetes resistance, histologic examination of pancreata from NOD BCIID mice revealed foci of noninvasive peri-insulitis that could be intentionally converted into a destructive process upon treatment with cyclophosphamide. We conclude that I-Ag7-mediated Ag presentation by B cells serves to overcome a checkpoint in T cell tolerance to islet beta cells after their initial targeting has occurred. Overall, this work indicates that the full expression of the autoimmune potential of anti-islet T cells in NOD mice is intimately regulated by B cell-mediated MHC class II Ag presentation.

Animals↗
PubMed1999

Contribution of the innate immune system to autoimmune diabetes: a role for the CR1/CR2 complement receptors.

B lymphocytes are required for diabetogenesis in nonobese diabetic (NOD) mice. The complement component of the innate immune system regulates B cell activation and tolerance through complement receptors CR1/CR2. Thus, it is important to assess the contribution of complement receptors to autoimmune diabetes in NOD mice. Examination of the lymphoid compartments of NOD mice revealed striking expansion of a splenic B cell subset with high cell surface expression of CR1/CR2. This subset of B cells exhibited an enhanced C3 binding ability. Importantly, long-term in vivo blockade of C3 binding to CR1/CR2 prevented the emergence of the CR1/CR2(hi) B cells and afforded resistance to autoimmune diabetes in NOD mice. These findings implicate complement as an important regulatory element in controlling the T cell-mediated attack on islet beta cells of NOD mice.

Animals↗
PubMed1999

Cardiac allograft tolerance induced by intra-arterial infusion of recombinant adenoviral CTLA4Ig.

BACKGROUND: Systemic administration of soluble recombinant fusion protein of cytotoxic T lymphocyte antigen 4 (CTLA4Ig) induces blockade of the CD28/B7 costimulatory pathway and promotes survival of allogeneic and xenogeneic grafts. We tested the efficacy of local expression of CTLA4Ig gene in the myocardium, induced by transduction with a recombinant adenovirus encoding the CTLA4Ig gene, on the survival of rat cardiac allografts. METHODS: The donor hearts were perfused ex vivo with recombinant adenovirus encoding CTLA4Ig cDNA (AdCTLA4Ig) via intra-aorta coronary artery before transplantation. The distribution and duration of CTLA4Ig transgene expression in the myocardium was assessed by reverse transcriptase polymerase chain reaction (RT-PCR) or in situ RT-PCR after transplantation. RESULTS: In situ RT-PCR demonstrated abundant expression of CTLA4Ig transgene in the endo-myocardium of AdCTLA4Ig-perfused cardiac grafts. Lewis and Brown Norway cardiac allografts transduced with AdCTLA4Ig survived indefinitely in nonimmunosuppressed Wistar Furth recipients. However, donor-strain skin grafts were rejected by long-term recipients of cardiac allografts, which also triggered the rejection of the primary heart grafts. CONCLUSIONS: A single ex vivo intra-aortic infusion of recombinant adenovirus encoding the CTLA4Ig gene induced efficient transduction of the endo-myocardium and promoted the permanent survival of cardiac allografts in nonimmunosuppressed hosts. Despite the beneficial effect of local immunosuppression on cardiac allograft survival, the strategy failed to promote a state of donor-specific peripheral tolerance.

Abatacept↗
PubMed1999

A direct method for the calculation of alloreactive CD4+ T cell precursor frequency.

BACKGROUND: Direct measurement of the precursor frequency of alloreactive CD4+ T cells has been impossible due to the lack of a specific means of determining the absolute number of daughter cells generated with each division in a repertoire of stimulated T cells. METHODS: Responder lymphocytes were fluorescently labeled and adoptively transferred into irradiated allogeneic stimulator mice or incubated in vitro with irradiated stimulator splenocytes. After a 65- to 70-hr stimulation period, responder cells were analyzed by flow cytometry. RESULTS: The precursor frequency of dividing CD4+ T cells was determined both in vivo and in vitro. The observed number of alloreactive daughter cells generated with each round of division was used to calculate the frequency of alloantigen-specific CD4+ T cells. CONCLUSIONS: A novel method for the direct calculation of the frequency of alloreactive CD4+ T cells is described. This technique allows the determination of changes in the frequency of alloreactive T cells that might underlie tolerance to alloantigens.

Animals↗
PubMed1999

Cutting edge: alloimmune responses against major and minor histocompatibility antigens: distinct division kinetics and requirement for CD28 costimulation.

Comparative study of alloimmune responses against major and minor histocompatibility Ags has been limited by the lack of suitable assays. Here, we use a bioassay that permits tracking of alloreactive CD4+ T cell populations as they proliferate in response to major or minor histocompatibility Ags in vivo. Division of alloreactive CD4+ T cells proceeded more rapidly in response to major histocompatibility Ags than minor Ags, although CD4+ T cells alloreactive to minor Ags had a similar capacity to divide successively up to eight times after stimulation. Allorecognition of minor histocompatibility Ags was highly dependent on CD28 costimulation, with the frequency of CD4+ T cells proliferating in response to minor Ags in the absence of CD28 costimulation reduced up to 20-fold. These findings highlight differences in signaling processes that lead to allorecognition of major and minor histocompatibility Ags and have implications on the design of interventions aimed at abrogating these responses.

Animals↗
PubMed1999

Prevention of autoimmune recurrence and rejection by adenovirus-mediated CTLA4Ig gene transfer to the pancreatic graft in BB rat.

Type 1 diabetes is the result of a selective destruction of pancreatic islets by autoreactive T-cells. Therefore, in the context of islet or pancreas transplantation, newly transplanted beta-cells are threatened by both recurrent autoimmune and alloimmune responses in recipients with type 1 diabetes. In the present study, using spontaneously diabetic BB rats, we demonstrate that whereas isolated islets are susceptible to autoimmune recurrence and rejection, pancreaticoduodenal grafts are resistant to these biological processes. This resistance is mediated by lymphohematopoietic cells transplanted with the graft, since inactivation of these passenger cells by irradiation uniformly rendered the pancreaticoduodenal grafts susceptible to recurrent autoimmunity. We further studied the impact of local immunomodulation on autoimmune recurrence and rejection by ex vivo adenovirus-mediated CTLA4Ig gene transfer to pancreaticoduodenal grafts. Syngeneic DR-BB pancreaticoduodenal grafts transduced with AdmCTLA4Ig were rescued from recurrent autoimmunity. In fully histoincompatible LEW-->BB transplants, in which rejection and recurrence should be able to act synergistically, AdmCTLA4Ig transduced LEW-pancreaticoduodenal allografts enjoyed markedly prolonged survival in diabetic BB recipients. In situ reverse transcription-polymerase chain reaction revealed that transferred CTLA4Ig gene was strongly expressed in both endocrine and exocrine tissues on day 3. These results indicate the potential utility of local CD28-B7 costimulatory blockade for prevention of alloimmune and autoimmune destruction of pancreatic grafts in type 1 diabetic hosts.

Abatacept↗
PubMed1998

Utility of adenoviral-mediated Fas ligand gene transfer to modulate islet allograft survival.

BACKGROUND: One of the best-defined mechanisms for the induction of apoptosis involves signaling via the cell surface molecule Fas, after binding of Fas ligand. Expression of Fas ligand is tightly regulated, being expressed primarily by T cells after activation, where it serves as a self-regulatory mechanism for immune responses. Fas ligand has also been found to be expressed constitutively at sites of immune privilege such as the testes and the anterior chamber of the eye. Recently, co-transplantation of Fas ligand-transfected myoblasts in association with islet cell allografts was shown to prolong islet allograft survival but only rarely led to indefinite graft survival. Graft rejection was associated with loss of Fas ligand on the myoblasts, suggesting that direct expression of the transgene on the islets might be more effective. METHODS: A replication-defective adenoviral construct containing murine Fas ligand (Ad/MFL) was prepared by homologous recombination. NIH 3T3 cells, rodent splenocytes, and murine islets were infected with Ad/MFL and examined in vitro for functional murine Fas ligand expression. Survival of Ad/MFL-infected islets was subsequently evaluated in vivo in both syngeneic and allogeneic islet transplantation models. RESULTS: Cell lines and islet allografts transfected with Ad/MFL expressed a functional Fas ligand, capable of inducing apoptosis (confirmed by three distinct assays for DNA fragmentation) in Fas+ targets, but not in Fas- controls. Furthermore, Ad/MFL was able to modify allogeneic immune responses in vitro, as addition of this virus, but not a control adenovirus, significantly reduced proliferation in a mixed lymphocyte reaction. Surprisingly, however, transplantation of islet allografts transfected with Ad/MFL resulted in long-term allograft survival in only 1 of 30 recipients. Moreover, adenoviral-mediated Fas ligand gene transfer was complicated by transient, dose-dependent islet dysfunction, perhaps contributing to the lack of long-term engraftment. CONCLUSION: These data suggest that adenoviral-mediated Fas ligand expression may impair normal islet function in vivo, and indicate that alternative strategies for Fas ligand transgene delivery may be required in this setting.

Adenoviridae↗
PubMed1998

Percutaneous thrombolysis and stent placement for the treatment of portal vein thrombosis after liver transplantation: long-term follow-up.

BACKGROUND: The durable use of percutaneous minimally invasive techniques for the treatment of portal venous thrombosis after liver transplant has not been widely described. This report illustrates two cases in which percutaneous thrombolysis, angioplasty, and endovascular stent placement were successfully used to treat portal vein thrombosis in patients with recent liver transplants. METHODS: Liver dysfunction was initially manifested by the elevation of liver enzymes or the development of marked ascites and confirmed in both cases by sonography and angiography. The occluded portal vein was accessed by either a transjugular transhepatic puncture or direct transhepatic catheterization. Intraportal thrombolytic infusion, angioplasty, and stent placement were accomplished without complication. RESULTS: At the most recent follow-up, portal vein patency had been maintained for 2.5 and 4.5 years. CONCLUSIONS: These results demonstrate the technical feasibility and long-term patency of angioplasty and endovascular stent placement for the treatment of portal vein thrombosis in liver transplant recipients.

Adult↗
PubMed1998

Organ transplantation in the twenty-first century.

Major advances in the understanding of the immunologic process responsible for organ or cellular transplant rejection, a dramatic improvement in available immunosuppressive drugs, development of more sophisticated surgical techniques, and important progress in posttransplant intensive care over the last 30 years have led to a remarkable improvement in success following organ transplantation. Whereas excellent short-term survival of most transplanted organs is readily achieved, graft loss because of chronic rejection and the worsening problem of organ donor shortage remain major concerns in the field of transplantation. Recent advances in immunosuppressive drugs, induction of immunologic tolerance, and gene therapy strategies may help to prolong organ allograft survival in the future. Revised criteria for organ donation and xenotransplantation may one day solve the problem of organ supply. Today, as we approach the next millennium, we are optimistic that the elusive goal of immunologic tolerance will be achieved and perhaps applied to animal tissue. Such will certainly be the challenge for the next century.

Forecasting↗
PubMed1997

Percutaneous management of a bladder-drained pancreas transplant pseudocyst by a transcystic approach.

BACKGROUND: We describe a 35-year-old male type 1 diabetic who underwent a cadaveric combined kidney-bladder-drained pancreas transplant with a duodenocystostomy for exocrine drainage who developed a large pelvic pseudocyst associated with a dilated pancreatic duct and an elevated serum amylase level. METHODS: Due to the risk of surgical revision and the possibility of creating a cutaneous fistula with conventional percutaneous drainage, a pseudocyst-to-bladder drainage was performed. After the procedure, the catheter was capped to allow drainage of the pancreatic secretions into the bladder. RESULTS: After drainage, the patient's serum amylase and lipase normalized along with resolution of the pseudocyst. The tube was removed after 19 weeks with no evidence of a recurrent pseudocyst and a normal serum amylase level. CONCLUSION: The percutaneous pseudocyst-cystostomy obviated the need for surgical revision of the exocrine gland drainage and thus eliminated the morbidity and the potential risk of graft loss associated with such surgery.

Adult↗
PubMed1997

Focal acute tubular necrosis in a renal allograft.

Nuclear imaging is used to evaluate renal allografts demonstrating delayed function after transplantation. Interpretation of the nuclear scan in the context of clinical data, provides helpful information in the management of the transplant recipient. The better quality of images obtained with technetium-99m mercaptoacetyltriglycine (Tc-99m MAG3) has made it the radiotracer of choice compared to technetium-99m diethylenetriamine pentaacetic acid (Tc-99m DTPA) for imaging of the renal allograft. Tc-99m MAG3 is cleared from the kidney by tubular secretion, whereas Tc-99m DTPA is cleared by glomerular filtration. In this report, we discuss a unique abnormality found on nuclear imaging of a renal allograft. Utilizing our understanding of the characteristic handling of various radiotracers by the kidney, we were able to demonstrate that the renal scan was consistent with an area of focal acute tubular necrosis in the newly transplanted kidney.

Adult↗