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A CD4+ T-cell subset inhibits antigen-specific T-cell responses and prevents colitis
CURRENT LITERATURE have been performed or are under way in an attempt to understand the relative merits of the different techniques. Standardization of CD34+ cell counting will be a valuable aid to laboratorians attempting to optimize procedures for handling these cells. This study performed at a single site compares one inhoase flow cytometric assay with a commercial microvolumetric assay (Stellar, BMI Corp., Mt View, CA). The microvolumetric assay was linear (r 2 ~ 0.98) over a wide range (5 to 1500 cells/pL). The coefficient of variation (CV) using peripheral blood samples ranged from 50% at concentrations < 1 0 cells/I.tL to 15% for samples at concentrations from 20 to 100 cells/i.tL. Smaller CVs were found for apheresis harvests which contained higher concentrations of cells. The microvolumetric method was simple to perform and had an assay turnaround time of 40 minutes, requiring less than 10 minutes of technical time. Readers interested in the possible use of microvolumetric fluorimetry for CD34 analysis will find this study most interesting. The device is not compared with traditional flow cytometry in a multinational sendaround study.
Evolution of a strain of CJD that induces BSE-liko plaques. Manuelidis L, Fritch VV, You-Gen X. Science 277:94-98, 1997. The rapid advances in knowledge concerning prion disease continue to address mechanisms of disease and the relationship between the bovine spongiform variety and the new variant of Creutzfeld-Jacob disease (nv-CJD). This study identifies a rodent variety of prion that may be useful in the study of spongiform encephalopathies. The disease was easily passed to susceptible rats who demonstrated activation of microglial cells. These cells, which share features of blood lymphocytes, are considered integral to the transmission of disease from blood to brain. Of note, the microglial cell activation occurred before the development of characteristic plaquelike lesions associated with bovine spongiform encephalopathy. Of even greater interest was the finding in these animals that the early stage of infection was associated with activation of splenic macrophages. Apolipoprotein J (ApoJ) staining was used as a marker for inflammation-associated cellular activation. ApoJ-positive macrophages were abundant in the spleen during early experimental infection. The observed changes in splenic macrophages were not associated with the accumulation of PrP fibril plaques. This was consistent with the notion that plaque formation is a late sign of disease and not reliable for early diagnosis. The authors make the hypothesis that future therapies may be directed against macrophage function in an attempt to interrupt the transmission of disease from blood macrophages to brain microglial cell.
The same prion strain causes nvCJD and BSE. Nature 389:448-450, 1997. Human BSE (News and Views). Almond ,I, Pattison J. Nature 389:437-438, 1997. These two articles provide insight regarding bovine spongiform encephalopathy (BSE) and the risk of the new human variant of Creutzfeld-Jacob disease (nv-CJD). One line of evidence emerges from a research group in Ediburgh that examined the incubation period of disease after the innoculation of different spongiform encephalopathies in a mouse strain
149 model. The characteristic incubation in mice following the innoculation of material from cows with bovine encepbalopathy differed from the incubation time following the innoculation of material from sheep, mink, or deer infected with a spongiform encephalopathy. The BSE incubation phenotype (as measured in the indicator mouse model) was maintained even after the bovine prion disease was spread to other species (eg, pig, goat, and sheep). As reported in this issue of Nature, the incubation time in mice for BSE was the same as for human nv-CJD. The second line of evidence that nv-CJD and BSE are the same disease comes from the study by Hill et al who examined the so-called "glycoform profiles" of the prions. These investigators subjected the prion protein to a protease and then examined the fragment size and the ratio of di-, mono-, and nonglycosylated forms of the enzymatically digested PrP protein. The profile of glycoform digestion may be characteristic of different prion strains and may serve as a "fingerprint" of the disease. In this issue, the authors report that nv-CJD in humans carries the same glycoform profile as BSE in cattle. In contrast, the glycoform profile for nv-CJD differed from that seen in sporadic CJD or in iatrogenic CJD produced from the injection of pituitary growth hormone. Thus far, 21 cases of nv-CJD have been identified in the United Kingdom and are suspected to have resulted from transmission via infected cattle. All of the patients examined thus far (and 40% of the population in the United Kingdom) are homozygous for methionine at position 129 in the prion protein. The data provided in this issue of Nature support the notion that nv-CJD is the human equivalent of BSE. Unfortunately (or, perhaps, fortunately) the data do not allow us to predict how many cases will ultimately emerge.
A CD4+ T-cell subset inhibits antigen-specific T-cell responses and prevents colitis. Groux H, O'Gara A, Bigler M, et al. Nature 389:737-742, 1997. Much work has focused on the search for T-suppressor clones that might be capable of active downregulation of immune responsiveness. Recent attention has been directed toward subsets of T cells, Thl and Th2 cells, which display different characteristic patterns of cytokine expression. This article describes work performed to identify a new subset of CD4+ cells that may participate in active immunosuppression. T-cell clones were prepared by chronic stimulation of mouse T cells with ovalbumin presented by splenic antigen-presenting cells in a media rich in IL-10. The resulting clones expressed IL-10 at high levels but IL-2 and IL-4 at low levels. The cells responded poorly to direct antigenic stimulation, In the absence of IL-10 at the time of antigenic stimulation, clones did not appear. The authors designate them " T r l " clones. Similar clones were produced from human peripheral blood by stimulating T cells with allogeneic monocytes in the presence of IL-10. Stimulation without IL-10 resulted in typical Th 1-type CD4+ cells. Important characteristics of Trl clones are the release of large quantities of the immunosuppressive cytokine IL- 10 and the low expression of the T-cell stimulatory cytokines IL-2 and IL-4. Using a mixed lymphocyte reaction generated in a novel transwell split-compartment reaction chamber, the authors showed that antigen-specific stimulation of Trl clones in the upper portion of the reaction well induced active immunosuppression of the mixed lymphocyte response to alloantigen in the lower portion of the reaction well.
150 The authors hypothesized that chronic stimulation of CD4 + T cells in the presence of IL-10 generates a subset of T cells that inhibit antigen-specific immune responses, Although more studies are needed on immunoregulatory subsets of T cells, the potential to exploit this subset of CD4+ T cells for diagnostic and therapeutic purposes in the field Of transplantation tolerance and autoimmunity is clear.
~clopidine and thrombotic thrombocytopenic 0urpura. Kupfer Y, TesslerS. N Engl J Med 337:1245, 1997. This brief report of cases of thrombotic thrombocytopenic purpura (TTP) apparently resulting from the use Of ticl0pidine should be of interest to practitioners in transfusion medicine who are called on to treat this serious disease. Ticlopidine is increasingly used by cardiologists in the treatment of ischemic heart disease. The drug is an antiplatelet agent that interferes with ADP-induced second-messenger signals for platelet activation. It is usually combined with aspirin and often with other agents (fibrinolytic activators or glycoprotein inhibitors). Ticlopidine has a slow onset and offset of action. The two primary case reports described in this letter to the editor were fatal, and the reference citations listed lead the reader to additional reports of ticlopidine-associated TTP. It is indeed interesting that an antiplatelet agent used in conjunction with aspirin should become associated with TTR Many clinicians might argue that a drug such as ticlopidine would be appropriate for use in the treatment of TTP. One might speculate that the drug has an effect on second-messenger systems within endothelial cells, presumably inhibiting the release of naturally occurring antithrombotic agents. In this sense, there may be an analogy to the inhibition of prostaglandin synthesis pathways (aspirin) and its dual effect on the generation of not only thromboxane A2 but also prostacycline. Decades ago, the introduction of ristocetin as an antibiotic had unexpected consequences on platelet function which have been applied in the exploration of Willebrand's syndromes. Likewise, the ultimate effects concerning the association between ticlopidine and TTP remain unknown. The answer to this mystery may be of greater value than the use of the drug as an antiplatelet agent.
CURRENT LITERATURE
P. falciparum rosetting mediated by a parasite-variant erythrocyte membrane protein and complement receptor 1. Rowe JA, Moulds JM, Newbold CI, Miller LH. Nature 388:292-295, 1997. Definition of the millennia-long relationship between human red blood cells and malaria will reveal basic secrets to evolution and the interaction of genetics and the environment in the development of disease. The mechanism for attachment of Plasmodiumfalciparum has been the subject of intense investigation ever since the role of the Duffy antigen and P knowlesci was first discovered. Interaction of the parasite with the red blood cell is far more complex than once thought. The red blood cell is not a passive structure in this relationship but. rather, is co-opted by the parasite to express on the erythrocyte surface proteins that are encoded by genes of the parasite. One of these proteins is the parasite-derived variant erthrocyte membrane protein (PfEMP1). PfEMP1 seems to mediate the binding of infected red blood cells to vascular endothelium and may be a pivotal protein in the invasion of infected cells into the liver and other organs. In this study, the process of erythrocyte rosetting was investigated. Rosetting as a process in which uninfected red blood cells form rosettes around infected cells. Rosetting is associated with severe cases of Pfalciparum infection observed in Africa. The authors found that rosetting was mediated by PfEMP1 expression on the infected cells. This was demonstrated in several ways, including expression of the protein in COS cells using a gene construct derived from the parasite var gene sequences which code for PfEMP1. Having identified the protein ligand, the investigators turned their attention toward the red blood cell receptor. A variety of rare cells known to be null for blood groups were screened. A Knops-null red blood cell had decreased rosetting. Because the complement receptor type 1 (CR1) structure is expressed on Knops, the authors focused on CR1. Using red blood cells known to be CRl-deficient, they showed that PfEMP1 binds to CR1, and that soluble CR1 can inhibit rosetting. Of particular interest, individuals of the Sl(a-) phenotype expressed a polymorphism of CR1 that bound PfEMP1 less avidly. It was postulated that P falciparum may have exerted a selective evolutionary pressure in favor of Sl(a-) individuals. This interesting article demonstrates the power of molecular methods in unraveling the mechanisms by which malaria has remained one of the leading causes of death throughout the world.
Evolution of a strain of CJD that induces BSE-liko plaques. Manuelidis L, Fritch VV, You-Gen X. Science 277:94-98, 1997. The rapid advances in knowledge concerning prion disease continue to address mechanisms of disease and the relationship between the bovine spongiform variety and the new variant of Creutzfeld-Jacob disease (nv-CJD). This study identifies a rodent variety of prion that may be useful in the study of spongiform encephalopathies. The disease was easily passed to susceptible rats who demonstrated activation of microglial cells. These cells, which share features of blood lymphocytes, are considered integral to the transmission of disease from blood to brain. Of note, the microglial cell activation occurred before the development of characteristic plaquelike lesions associated with bovine spongiform encephalopathy. Of even greater interest was the finding in these animals that the early stage of infection was associated with activation of splenic macrophages. Apolipoprotein J (ApoJ) staining was used as a marker for inflammation-associated cellular activation. ApoJ-positive macrophages were abundant in the spleen during early experimental infection. The observed changes in splenic macrophages were not associated with the accumulation of PrP fibril plaques. This was consistent with the notion that plaque formation is a late sign of disease and not reliable for early diagnosis. The authors make the hypothesis that future therapies may be directed against macrophage function in an attempt to interrupt the transmission of disease from blood macrophages to brain microglial cell.
The same prion strain causes nvCJD and BSE. Nature 389:448-450, 1997. Human BSE (News and Views). Almond ,I, Pattison J. Nature 389:437-438, 1997. These two articles provide insight regarding bovine spongiform encephalopathy (BSE) and the risk of the new human variant of Creutzfeld-Jacob disease (nv-CJD). One line of evidence emerges from a research group in Ediburgh that examined the incubation period of disease after the innoculation of different spongiform encephalopathies in a mouse strain
149 model. The characteristic incubation in mice following the innoculation of material from cows with bovine encepbalopathy differed from the incubation time following the innoculation of material from sheep, mink, or deer infected with a spongiform encephalopathy. The BSE incubation phenotype (as measured in the indicator mouse model) was maintained even after the bovine prion disease was spread to other species (eg, pig, goat, and sheep). As reported in this issue of Nature, the incubation time in mice for BSE was the same as for human nv-CJD. The second line of evidence that nv-CJD and BSE are the same disease comes from the study by Hill et al who examined the so-called "glycoform profiles" of the prions. These investigators subjected the prion protein to a protease and then examined the fragment size and the ratio of di-, mono-, and nonglycosylated forms of the enzymatically digested PrP protein. The profile of glycoform digestion may be characteristic of different prion strains and may serve as a "fingerprint" of the disease. In this issue, the authors report that nv-CJD in humans carries the same glycoform profile as BSE in cattle. In contrast, the glycoform profile for nv-CJD differed from that seen in sporadic CJD or in iatrogenic CJD produced from the injection of pituitary growth hormone. Thus far, 21 cases of nv-CJD have been identified in the United Kingdom and are suspected to have resulted from transmission via infected cattle. All of the patients examined thus far (and 40% of the population in the United Kingdom) are homozygous for methionine at position 129 in the prion protein. The data provided in this issue of Nature support the notion that nv-CJD is the human equivalent of BSE. Unfortunately (or, perhaps, fortunately) the data do not allow us to predict how many cases will ultimately emerge.
A CD4+ T-cell subset inhibits antigen-specific T-cell responses and prevents colitis. Groux H, O'Gara A, Bigler M, et al. Nature 389:737-742, 1997. Much work has focused on the search for T-suppressor clones that might be capable of active downregulation of immune responsiveness. Recent attention has been directed toward subsets of T cells, Thl and Th2 cells, which display different characteristic patterns of cytokine expression. This article describes work performed to identify a new subset of CD4+ cells that may participate in active immunosuppression. T-cell clones were prepared by chronic stimulation of mouse T cells with ovalbumin presented by splenic antigen-presenting cells in a media rich in IL-10. The resulting clones expressed IL-10 at high levels but IL-2 and IL-4 at low levels. The cells responded poorly to direct antigenic stimulation, In the absence of IL-10 at the time of antigenic stimulation, clones did not appear. The authors designate them " T r l " clones. Similar clones were produced from human peripheral blood by stimulating T cells with allogeneic monocytes in the presence of IL-10. Stimulation without IL-10 resulted in typical Th 1-type CD4+ cells. Important characteristics of Trl clones are the release of large quantities of the immunosuppressive cytokine IL- 10 and the low expression of the T-cell stimulatory cytokines IL-2 and IL-4. Using a mixed lymphocyte reaction generated in a novel transwell split-compartment reaction chamber, the authors showed that antigen-specific stimulation of Trl clones in the upper portion of the reaction well induced active immunosuppression of the mixed lymphocyte response to alloantigen in the lower portion of the reaction well.
150 The authors hypothesized that chronic stimulation of CD4 + T cells in the presence of IL-10 generates a subset of T cells that inhibit antigen-specific immune responses, Although more studies are needed on immunoregulatory subsets of T cells, the potential to exploit this subset of CD4+ T cells for diagnostic and therapeutic purposes in the field Of transplantation tolerance and autoimmunity is clear.
~clopidine and thrombotic thrombocytopenic 0urpura. Kupfer Y, TesslerS. N Engl J Med 337:1245, 1997. This brief report of cases of thrombotic thrombocytopenic purpura (TTP) apparently resulting from the use Of ticl0pidine should be of interest to practitioners in transfusion medicine who are called on to treat this serious disease. Ticlopidine is increasingly used by cardiologists in the treatment of ischemic heart disease. The drug is an antiplatelet agent that interferes with ADP-induced second-messenger signals for platelet activation. It is usually combined with aspirin and often with other agents (fibrinolytic activators or glycoprotein inhibitors). Ticlopidine has a slow onset and offset of action. The two primary case reports described in this letter to the editor were fatal, and the reference citations listed lead the reader to additional reports of ticlopidine-associated TTP. It is indeed interesting that an antiplatelet agent used in conjunction with aspirin should become associated with TTR Many clinicians might argue that a drug such as ticlopidine would be appropriate for use in the treatment of TTP. One might speculate that the drug has an effect on second-messenger systems within endothelial cells, presumably inhibiting the release of naturally occurring antithrombotic agents. In this sense, there may be an analogy to the inhibition of prostaglandin synthesis pathways (aspirin) and its dual effect on the generation of not only thromboxane A2 but also prostacycline. Decades ago, the introduction of ristocetin as an antibiotic had unexpected consequences on platelet function which have been applied in the exploration of Willebrand's syndromes. Likewise, the ultimate effects concerning the association between ticlopidine and TTP remain unknown. The answer to this mystery may be of greater value than the use of the drug as an antiplatelet agent.
CURRENT LITERATURE
P. falciparum rosetting mediated by a parasite-variant erythrocyte membrane protein and complement receptor 1. Rowe JA, Moulds JM, Newbold CI, Miller LH. Nature 388:292-295, 1997. Definition of the millennia-long relationship between human red blood cells and malaria will reveal basic secrets to evolution and the interaction of genetics and the environment in the development of disease. The mechanism for attachment of Plasmodiumfalciparum has been the subject of intense investigation ever since the role of the Duffy antigen and P knowlesci was first discovered. Interaction of the parasite with the red blood cell is far more complex than once thought. The red blood cell is not a passive structure in this relationship but. rather, is co-opted by the parasite to express on the erythrocyte surface proteins that are encoded by genes of the parasite. One of these proteins is the parasite-derived variant erthrocyte membrane protein (PfEMP1). PfEMP1 seems to mediate the binding of infected red blood cells to vascular endothelium and may be a pivotal protein in the invasion of infected cells into the liver and other organs. In this study, the process of erythrocyte rosetting was investigated. Rosetting as a process in which uninfected red blood cells form rosettes around infected cells. Rosetting is associated with severe cases of Pfalciparum infection observed in Africa. The authors found that rosetting was mediated by PfEMP1 expression on the infected cells. This was demonstrated in several ways, including expression of the protein in COS cells using a gene construct derived from the parasite var gene sequences which code for PfEMP1. Having identified the protein ligand, the investigators turned their attention toward the red blood cell receptor. A variety of rare cells known to be null for blood groups were screened. A Knops-null red blood cell had decreased rosetting. Because the complement receptor type 1 (CR1) structure is expressed on Knops, the authors focused on CR1. Using red blood cells known to be CRl-deficient, they showed that PfEMP1 binds to CR1, and that soluble CR1 can inhibit rosetting. Of particular interest, individuals of the Sl(a-) phenotype expressed a polymorphism of CR1 that bound PfEMP1 less avidly. It was postulated that P falciparum may have exerted a selective evolutionary pressure in favor of Sl(a-) individuals. This interesting article demonstrates the power of molecular methods in unraveling the mechanisms by which malaria has remained one of the leading causes of death throughout the world.