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J L Platt

Publications and source records attributed to J L Platt.

At least 37 records · Page 2Linked to original sources
PubMed2001

Xenotransplantation and other means of organ replacement.

Exciting new technologies, such as cellular transplantation, organogenesis and xenotransplantation, are thought to be promising approaches for the treatment of human disease. The feasibility of applying these technologies, however, might be limited by biological and immunological hurdles. Here, we consider whether, and how, xenotransplantation and various other technologies might be applied in future efforts to replace or supplement the function of human organs and tissues.

Animals↗
PubMed2000

The role of anti-Galalpha1-3Gal antibodies in acute vascular rejection and accommodation of xenografts.

BACKGROUND: A major impediment to the transplanting of porcine organs into humans is the susceptibility of porcine organs to acute vascular rejection, which can destroy a vascularized xenograft over a period of hours to days. Acute vascular rejection of porcine-to-primate xenografts is thought to be triggered by binding of xenoreactive antibodies to the graft. We tested whether antibodies, binding to Galalpha1-3Gal epitopes in porcine tissue, initiate this phenomenon. METHODS AND RESULTS: Specific depletion of anti-Galalpha1-3Gal antibodies from the blood of baboons, using extracorporeal perfusion of separated plasma through columns of Sepharose beads covalently linked to the antigenic trisaccharide, Galalpha1-3Galbeta1-4GlcAc, averted the development of acute vascular rejection in porcine organs transgenic for human decay-accelerating factor and CD59. More importantly, after immunodepletion was stopped and Gala1-3Gal antibodies were allowed to return, these same organs continued to function and remained pathologically normal and thus seemed to achieve a state of accommodation. CONCLUSION: These results demonstrate that anti-Galalpha1-3Gal antibodies cause acute vascular rejection and suggest that depletion of these antibodies leads to accommodation of the donor cardiac xenograft and could supply an important model for additional study.

Acute Disease↗
PubMed2000

Natural anti-carbohydrate IgM in mice: dependence on age and strain.

Natural anti-carbohydrate antibodies in humans play a key role in natural immunity and in recognition of allogeneic and xenogeneic antigens. Presumably, natural anti-carbohydrate antibodies in mice have similar functions; but these antibodies have not been extensively characterized. An assay was developed and used to screen for anti-carbohydrate IgM in the serum of BDF-1 mice. Among the natural anti-carbohydrate IgM identified, anti-betaGlcNAc IgM were the most abundant. Anti-betaGlcNAc IgG was not detected. Levels of anti-betaGlcNAc IgM were very low in 3-week-old BDF-1 mice and increased until 5 to 7 months of age. Levels of serum anti-betaGlcNAc IgM similar to those in BDF-1 mice were found in the serum of some strains related to the BDF-1 strain (DBA and C57BL/6) and in BDF mice lacking the galactosyl transferase gene. However, in two strains unrelated to the BDF-1 strain (FVB and SJL), levels of anti-betaGlcNAc IgM were less than one-tenth of those found in BDF-1 mice. These results provide considerable insight into the effect of age on the production of natural anti-carbohydrate antibodies in mice and indicate that production of those antibodies is strongly dependent on the strain of mouse. These studies will help in future development of murine models for studying the biological and medical roles of natural anti-carbohydrate antibodies.

Acetylglucosamine↗
PubMed2000

Phenotypic and functional maturation of dendritic cells mediated by heparan sulfate.

Primary immune responses are thought to be induced by dendritic cells. To promote such responses, dendritic cells must be activated by exogenous agonists, such as LPS, or by products of activated leukocytes, such as TNF-alpha and IL-1. How dendritic cells might be activated in the absence of exogenous stimuli, or without the immediate presence of activated leukocytes, as might occur in immunity to tumor cells or transplants, is unknown. We postulated that heparan sulfate, an acidic, biologically active polysaccharide associated with cell membranes and extracellular matrices, which is rapidly released under conditions of inflammation and tissue damage, might provide such a stimulus. Incubation of immature murine dendritic cells with heparan sulfate induced phenotypic maturation evidenced by up-regulation of I-A, CD40, CD54 (ICAM-1), CD80 (B7-1), and CD86 (B7-2). Dendritic cells exposed to heparan sulfate exhibited a markedly lowered rate of Ag uptake and increased allostimulatory capacity. Stimulation of dendritic cells with heparan sulfate induced release of TNF-alpha, IL-1beta, and IL-6, although the maturation of dendritic cells was independent of these cytokines. These results suggest that soluble heparan sulfate chains, as products of the degradation of heparan sulfate proteoglycan, might induce maturation of dendritic cells without exogenous stimuli, thus contributing to the generation and maintenance of primary immune responses.

Animals↗
PubMed2000

Altered intragraft immune responses and improved renal function in MHC class II-deficient mouse kidney allografts.

BACKGROUND: During renal allograft rejection, expression of MHC class II antigens is up-regulated on the parenchymal cells of the kidney. This up-regulation of MHC class II proteins may stimulate the intragraft alloimmune response by promoting their recognition by recipient CD4+ T cells. In previous studies, absence of donor MHC class II antigens did not affect skin graft survival, but resulted in prolonged survival of cardiac allografts. METHODS: To further explore the role of MHC class II antigens in kidney graft rejection, we performed vascularized kidney transplants using donor kidneys from A(beta)b-deficient mice that lack MHC class II expression. RESULTS: At 4 weeks after transplant, GFR was substantially depressed in control allografts (2.18+/-0.46 ml/min/kg) compared to nonrejecting isografts (7.98+/-1.62 ml/min/kg; P<0.01), but significantly higher in class II- allografts (4.38+/-0.60 ml/min/kg; P<0.05). Despite the improvement in renal function, class II- allograft demonstrated histologic features of acute rejection, not unlike control allografts. However, morphometric analysis at 1 week after transplantation demonstrated significantly fewer CD4+ T cells infiltrating class II- allografts (12.8+/-1.2 cells/mm2) compared to controls (25.5+/-2.6 cells/mm2; P=0.0007). Finally, the intragraft profile of cytokines was altered in class II- allografts, with significantly reduced expression of Th2 cytokine mRNA compared to controls. CONCLUSIONS: These results support a role of MHC class II antigens in the kidney regulating immune cells within the graft. Further, effector pathways triggered by class II antigens promote renal injury during rejection.

Animals↗
PubMed2000

Endothelial cell activation by pore-forming structures: pivotal role for interleukin-1alpha.

BACKGROUND: Interaction of complement with endothelial cells (ECs) underlies the development of inflammation and coagulation in disease. Assembly of the membrane attack complex (MAC) of complement on EC membrane, like stimulation with cytokines, upregulates tissue factor and cyclooxygenase-2 but does so via the intermediary action of IL-1alpha. We asked whether the MAC activates porcine aortic and microvascular ECs in a global manner by this mechanism and whether this mechanism is used by membrane pore-forming structures. METHODS AND RESULTS: Exposure of ECs to complement caused upregulation of mRNAs for E-selectin, intracellular adhesion molecule-1, vascular cell adhesion molecule-1, Ikappa-Balpha, interleukin (IL)-1alpha, IL-1beta, IL-8, and plasminogen activator inhibitor-1 over a period of 6 hours. The expression of these genes was not a primary response to stimulation, however, because IL-1 receptor antagonist inhibited expression of these genes. Activation of ECs by complement depended on the autocrine action of IL-1alpha, because complement-mediated EC activation was inhibited by anti-IL-1alpha antibodies. Melittin and mastoparan, amphiphilic pore-forming peptides like the MAC, induced E-selectin through intermediary action of IL-1. CONCLUSIONS: These findings suggest that transmembrane pore-forming proteins, as a class of molecules, activate ECs through the autocrine effects of IL-1alpha.

Animals↗
PubMed2000

Expression of tissue factor mRNA in cardiac xenografts: clues to the pathogenesis of acute vascular rejection.

BACKGROUND: Acute vascular rejection destroys vascularized xenografts over a period of hours to days and is now considered the major hurdle to the clinical application of xenotransplantation. The hallmark of acute vascular rejection is diffuse intravascular coagulation; however, the pathogenesis of coagulation is a matter of controversy. One line of evidence points to activated endothelial cells and another to activated inflammatory cells as a source of tissue factor and thus as a primary cause of this lesion. The distinction between the two mechanisms inducing coagulation in the xenograft provides an opportunity for specific intervention. METHODS: To explore these mechanisms, we studied the expression of tissue factor mRNA by in situ reverse transcriptase-polymerase chain reaction in relation to the histopathologic manifestations of acute vascular rejection in guinea pig hearts transplanted into rats treated by cobra venom factor to avoid the hyperacute rejection. RESULTS: Three hours after transplantation and before the deposition of fibrin, tissue factor mRNA was expressed in the endothelial cells lining small and medium blood vessels and in smooth muscle cells of guinea pig cardiac xenografts. Sixteen hours after transplantation, while rat tissue factor mRNA was expressed only in occasional infiltrating cells, cardiac xenografts showed prominent deposits of fibrin in small vessels. Maximum expression of tissue factor on rat infiltrating cells was observed 48 hr after transplantation. CONCLUSIONS: These results suggest that in acute vascular rejection, coagulation is initiated on the donor vascular system, while the procoagulant characteristics of infiltrating cells may reflect a response to tissue injury rather than a cause.

Acute Disease↗
PubMed2000

Bile acids in xenogeneic ex-vivo liver perfusion: function of xenoperfused livers and compatibility with human bile salts and porcine livers.

BACKGROUND: In recent years, hepatic support systems using xenogeneic cells have been developed to support patients in fulminant hepatic failure. The extent to which xenogeneic hepatocytes metabolize and excrete human organic anions is unclear. In these studies we examined the ability of the ex vivo porcine liver to clear human bile acids during extracorporeal liver perfusion (ELP). METHODS: Four patients with fulminant hepatic failure underwent extracorporeal liver perfusion with 9 porcine livers. The venovenous circuit was designed as previously described (NEJM,1994,331:234) as were the immunologic features (Transplantation 1994,58:1162). Bile from the porcine liver and serum samples were collected hourly during perfusion. Three bile acids (glycocholic, glycodeoxycholic, taurodeoxycholic acid) were selected as markers for human bile and three (glycohyocholic, glycohyodeoxycholic, and glyco-3alpha-hydroxy-6-oxo-5beta-cholanoic acid) for markers of pig bile. Bile acids from both serum and bile were processed and analyzed through high performance liquid chromatography. The Students' t test was used for statistical analysis. RESULTS: The mean duration of perfusions was 4.1+/-1.5 hr. The mean total bile acid clearance from serum (243+/-44 micromol/h) was similar to the total bile acid biliary excretion (286+/-84 micromol/hr, P = 0.06). After 1 hr of perfusion, bile samples demonstrated a predominance of pig bile salts (65%). After 3 hr of perfusion, human bile acids made up 85% of total biliary bile acids. Pig bile acids appeared in patients' sera after 1 hr of perfusion, and after 3 hr, 35% of serum bile salts were pig-specific. CONCLUSIONS: Porcine livers perfused with human blood can clear the serum of potentially toxic human bile acids and excrete them into bile. Simultaneously, the percentage of pig-specific bile acids in patient serum increases during xenogeneic perfusion for unknown reasons. The relative hepatic uptake of bile acid from serum is similar to bile acid excretion in bile. Further development of systems using porcine livers or hepatocytes is warranted.

Animals↗
PubMed2000

Influence of human fulminant hepatic failure sera on endogenous retroviral expression in pig hepatocytes.

A porcine endogenous retrovirus (PERV) has been shown to infect human embryonic kidney 293 (HEK293) cells in vitro. The PERV proviral sequence exists in the genome of all porcine cells, including hepatocytes used in a bioartificial liver (BAL). We examined the possibility of PERV infection in HEK293 cells during exposure to supernatant from cultured pig hepatocytes. Pig hepatocytes were cultured in media supplemented with serum from patients in fulminant hepatic failure (FHF) to simulate conditions of an extracorporeal BAL. Pig hepatocytes were cultured in serum-free media for 24 hours and then exposed to fresh medium containing serum from a patient with FHF (22 patients tested). Twenty-four hours later, supernatant was collected and analyzed by polymerase chain reaction (PCR), with and without reverse transcriptase. Primers targeting the pol gene of PERV were used for PCR. Products of amplification were detected by an enzyme-linked immunosorbent assay-based technique using an internal capture probe also targeting the pol gene. Levels of PERV sequences were estimated by serial dilution. All positive samples were tested for infectivity in HEK293 cells. Porcine kidney 15 cell supernatant and fresh culture media were studied as positive and negative controls, respectively. Pig hepatocytes were also studied in the absence of FHF sera and in the presence of mitogenic stimulation with phytohemagglutinin (PHA) and phorbol 12-myristate-13-acetate (PMA). PERV DNA and PERV RNA were detected in all supernatants of cultured pig hepatocytes. The level of PERV RNA in the supernatant of pig hepatocytes was not altered by exposure to human FHF serum or stimulation with PHA and PMA. In addition, PERV RNA was undetectable in the supernatant of HEK293 cells for up to 50 days after exposure to pig hepatocyte supernatant (with or without FHF sera). These findings show that production of PERV by cultured pig hepatocytes was unaffected by exposure to growth factors and cytokines present in human FHF sera.

Animals↗
PubMed2000

Immunobiology of xenotransplantation.

The transplantation of organs between disparate species is hindered by severe immune responses of the recipient against the graft. These immune responses gives rise to hyperacute and acute vascular rejection and to cellular rejection. Research during the past decade has shed light on the elements of the immune system responsible for the rejection of xenografts and has provided novel and incisive therapies which might be applied to these problems.

Acute Disease↗