Biomedical subjects
Publications and source records attributed to N Young.
This article summarizes the current medical literature regarding the effects of viral infections upon the hematopoietic system. The article discusses the effect of viral infections upon peripheral blood counts, cellular immune system, and the bone marrow. In addition, a few selected syndromes, including human parvovirus, EBV, and HTLV infections, are discussed.
B19 parvovirus, the cause of fifth disease and transient aplastic crisis, has been successfully propagated in suspension cultures of human erythroid bone marrow cells obtained from patients with sickle cell disease and stimulated by erythropoietin. B19 inoculation in vitro resulted in a marked decline in identifiable erythroid cells over seven to nine days of incubation. Characteristic giant early erythroid cells were seen on Wright's-Giemsa stain of infected cultures. By in situ hybridization, 30% to 40% of erythroblasts were infected at 48 hours; a similar proportion of cells showed B19 capsid protein by immunofluorescence. B19 DNA was present in erythroblasts but not in the leukocyte fraction of bone marrow. B19 replication, as determined by Southern analysis, and B19 encapsidation, as determined by sensitivity of isolated cell fractions to DNase I, were restricted to the nuclei. B19 DNA was detectable in the nuclei from infected cultures beginning at 18 hours and in the supernatant at 32 hours; B19 genome copy number was estimated at about 25,000 to 30,000/infected cell at 48 hours. Recovery of virus depended on the multiplicity of infection (moi); at low moi, approximately 200x input virus was recovered from total cultures and 50x from the culture supernatants. Virus released into the supernatant was as infectious or more infectious than virus obtained from sera of infected patients. Human erythroid bone marrow culture represents a safe in vitro system for the elucidation of the cellular and molecular biology of the pathogenic B19 parvovirus.
The B19 parvovirus is responsible for at least three human diseases. The virus was successfully propagated in suspension cultures of human erythroid bone marrow from patients with hemolytic anemias; release of newly synthesized virus into the supernatants of infected cultures was observed. This culture system allowed study at a molecular level of events associated with the B19 life cycle. The B19 parvovirus replicated through high molecular weight intermediate forms, linked through a terminal hairpin structure. B19 replication in vitro was highly dependent on the erythropoietic content of cultures and on addition of the hormone erythropoietin.
Human parvovirus (HPV) infection has recently been implicated as the cause of aplastic crisis in patients with hemolytic anemias such as congenital spherocytosis and sickle cell anemia. The virus causes a transient red cell aplasia which, in patients with a shortened red cell life span, is manifested as a rapid worsening of the anemia and an absence of peripheral reticulocytosis. Recovery is associated with the presence of giant pronormoblasts in the bone marrow, and several days later, a brisk peripheral reticulocytosis. In normal subjects, HPV causes erythema infectiosum (fifth disease) but is not associated with symptomatic anemia, probably because of the duration of the normal red blood cell life span. A case of HPV infection producing severe anemia in an immunocompromised patient without an underlying hemolytic anemia is presented here. Infection in this patient, a 3-year-old boy with acute lymphoblastic leukemia in remission, may have been prolonged by immunosuppression, leading over a 4-week period to a severe anemia. The immunosuppressed appear to be another group of patients at risk of developing symptomatic anemia when infected by HPV.
Explore the source record for details and available documents.
We have analyzed natural killer (NK) cells in 43 patients with severe aplastic anemia, using cytotoxicity assays and microfluorometry with monoclonal antibodies, prior to and after treatment with antithymocyte globulin (ATG). Before treatment, natural killer cell activity (NKa) in both peripheral blood and bone marrow was markedly decreased in 76% of patients as compared with normal controls. Although we have measured low NKa in patients receiving large numbers of blood transfusions (means = 150 U of RBCs), six aplastic patients had low NKa in the absence of transfusions, and the average number of transfusions in the total population was low (means = 24). Purification of larger granular lymphocytes (LGLs) from peripheral blood of aplastic anemia patients failed to recover significant NKa. Most of these large granular lymphocytes showed few azurophilic granules. NKa was appropriately enhanced in these patients samples by exposure of mononuclear cells to either interleukin 2 (IL-2) or interferon (IFN). Analysis of peripheral blood phenotypic markers showed that cells bearing Leu 7 antigen were in the normal range in aplastic anemia (means = 12% +/- 2%; normal = 16% +/- 2%), but there was a deficiency of Leu 11+ cells (means = 8% +/- 2%; normal = 15% +/- 2%). The number of Leu 11+ cells was well correlated with NKa. In 13 of 22 patients treated with ATG, NKa returned to the normal range, and recovery of NKa was correlated to hematopoietic recovery. Our results suggest that deficient NKa is an intrinsic feature of aplastic anemia, and that the circulating cells in this disease are of the pre-NK cell stage.
We studied the relationship between paroxysmal nocturnal hemoglobinuria (PNH) and bone marrow failure using in vitro hematopoietic colony culture assays. Most of 17 patients with PNH showed decreased colony formation, by erythroid burst-forming cells (BFU-E) and granulocyte-macrophage colony-forming cells (CFU-C) in methylcellulose, disproportionate to their degree of bone marrow biopsy cellularity. Only a minority of the hematopoietic progenitors were sensitive to complement-mediated lysis in vitro. In contrast, normoblasts from maturing erythroid bursts removed from culture and exposed to acidified serum were sensitive to complement-mediated lysis. The size of bursts and the sensitivity of their progeny correlated strongly, suggesting that the PNH defect was acquired in culture as a function of the generational age of erythroid precursor cells. In addition, BFU-E of PNH patients were very sensitive to 3H-thymidine suicide, in comparison with normal individuals and patients with other hemolytic anemias, indicating that a large proportion of primitive erythroid progenitors in PNH bone marrow were in cell cycle. All of these results imply that acquisition of the PNH defect during erythropoiesis may lead to intramedullary destruction of developing erythroid cells. The increased demand that results on the progenitor pool may lead to stem cell depletion and bone marrow failure.
Five patients with chronic non-A, non-B hepatitis were entered into a pilot therapeutic study of the antiviral agent acyclovir [9-(2-hydroxyethoxymethyl)guanine]. Each patient received acyclovir by slow intravenous infusion in a dosage of 5 mg/kg every 8 hr for 10 days. During therapy, serum aminotransferase levels decreased by more than 50% in two patients, remained unchanged in two patients, and rose (by 32%) in the final patient. The two patients whose serum aminotransferase levels decreased during acyclovir treatment subsequently received a second course of drug using a higher dose (10 mg/kg every 8 hr for 10 days). Serum aminotransferase levels rose in both patients (by 54% and 121%) during the second course of therapy. Acyclovir was well tolerated in these patients, and there were no symptoms or signs attributable to drug toxicity during or after treatment. During a subsequent 12-month follow-up period, none of the five patients has manifested either a clinical or serum biochemical improvement in their chronic liver disease. Spontaneous fluctuations in serum aminotransferase levels unrelated to acyclovir therapy were noted in three of the five patients. These findings suggest that a short course of acyclovir does not have any appreciable long-term beneficial effect on the course of chronic non-A, non-B hepatitis.
The ease with which HbF production can be increased in subjects with SS disease was a totally unexpected phenomena on the basis of previous models of HbF synthesis. The fact that these drugs induce rapid increases in F cell production and increase HbF per F cell and HbS in non-F cells, may be important clues as to the mechanism of the action of these drugs. It is far from clear whether either one of these agents will be eventually used as therapy for subjects with SS disease. The more recent problems with cytotoxicity illustrated by HU, and the potential carcinogenic effect of 5-aza limit our ability to perform large controlled clinical trials at this time. The observation that HbF production is increased by two agents which perturb DNA replication may be important clues in understanding not only the origins of differential gamma versus beta globin gene expression but also the mechanism by which HbF is restricted to expression in only certain cells during normal erythroid maturation.
Protein kinase C is synergistically activated by the presence of calcium, certain phospholipids and a diacylglycerol. The physiological activation of the enzyme appears to be determined by the availability of the diacylglycerol which is itself a product of (poly) phosphoinositol turnover. It is shown here that the diacylglycerol activation effect is stereospecific, with only the 1,2-sn-diglycerides being active. This demonstrates for the first time a stereospecific effector role for a membrane-bound lipid. Furthermore, this work strengthens the link forged between the highly potent and specific tumor promoters (such as the phorbol esters) and the diglycerides as activators of protein kinase C.
Explore the source record for details and available documents.
A bichromatic method is described for the determination of salicylate using a micro centrifugal analyzer. Salicylate was quantitated based on its reaction with ferric ion to produce a violet-colored complex. The method provides sample blanking and allows for rapid determination of salicylate levels in serum.
Lymphocyte subsets have been measured in the blood of 28 patients with aplastic anaemia. The mean helper/inducer:suppressor/cytotoxic T lymphocyte ratio (1.24 +/- 0.74) was significantly decreased in the total population in comparison to mean ratios in a normal population (1.78 +/- 0.57) and in patients with other haematological diseases (1.82 +/- 0.92). A reversed ratio (less than or equal to 1) was present in a large proportion (53%) of aplastic patients, due both to an absolute deficiency of helper/inducer lymphocytes and an increase in suppressor/cytotoxic lymphocytes. Increased HLA-DR expression, evidence of lymphocyte activation, was present in seven of 12 patients evaluated and was confined to the suppressor/cytotoxic lymphocyte population. In the bone marrow, the percentage of lymphocytes was increased two-fold compared to normal bone marrow but the ratio of T cell subsets was not abnormal. Two of four patients evaluated after haematopoietic recovery following ATG treatment showed a return to normal of the T4/T8 ratio; in two others a low T4/T8 ratio persisted despite recovery. These results indicate that lymphocyte subset imbalance and lymphocyte activation are present in many patients with aplastic anaemia, either as a contributing factor or as a result of bone marrow failure.
The human parvovirus (HPV), the cause of transient aplastic crisis of hereditary hemolytic anemia, has been shown to be cytotoxic for erythroid progenitor cells and its presence in these cells demonstrated by morphologic techniques. A relatively pure population of progenitors, isolated by removal of immature erythroid bursts from primary culture, was the target of the virus infection. Infected cells failed to proliferate in secondary culture. Using a monoclonal antibody to HPV, specific fluorescence was demonstrated in a minority of cells 24-48 h after infection with virus. Infected cells examined by electron microscopy showed marked toxic ultrastructural alterations and parvovirus-like particles in crystalline arrays in the nucleus.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Educational imagery is a classroom teaching methodology that allows students to mentally isolate themselves and to use their natural abilities to daydream or fantasize in ways that accomplish educational objectives. Educational imagery is used to facilitate decision making, clarify values, memorize, incorporate behavioral outcomes of teaching, and reinforce cognitive concepts. The technique can help allied health students prepare for the clinical setting. The behavioral components, ethical concerns, and decision making that will occur in the clinical setting can be rehearsed in the classroom before the actual experience by guiding students' imagination. This article describes the nature of imagery and its sources, describes how to implement the strategy in the classroom, and gives examples of educational imagery strategies for the allied health disciplines.