Self-regulation of E x B flow shear via plasma turbulence.

The momentum balance has been applied to the ExB flow in the edge region of a reversed field pinch (RFP) configuration. All terms, including those involving fluctuations, have been measured in stationary condition in the edge region of the Extrap-T2R RFP experiment. It is found that the component of the Reynolds stress driven by electrostatic fluctuations is the term playing the major role in driving the shear of the ExB flow to a value marginal for turbulent suppression, so that the results are in favor of a turbulence self-regulating mechanism underlying the momentum balance at the edge. Balancing the sheared flow driving and damping terms, the plasma viscosity is found anomalous and consistent with the diffusivity due to electrostatic turbulence.

Vortex-induced diffusivity in reversed field pinch plasmas.

Coherent structures identified in two reversed field pinch experiments are interpreted as a dynamic balance of dipolar and monopolar vortices growing and evolving under the effect of the ExB flow shear. For the first time their contribution to the anomalous transport has been estimated in fusion related plasmas, showing that they can account for up to 50% of the total plasma diffusivity. The experimental findings indicate that the diffusion coefficient associated with the coherent structures depends on the relative population of the two types of vortices and is minimum when the two populations are equal. An interpretative model is proposed to explain this feature.

Feedback stabilization of multiple resistive wall modes.

Active feedback stabilization of multiple independent resistive wall modes is experimentally demonstrated in a reversed-field pinch plasma. A reproducible simultaneous suppression of several nonresonant resistive wall modes is achieved. Coupling of different modes due to the limited number of the feedback coils is observed in agreement with theory. The feedback stabilization of nonresonant RWMs also has an effect on tearing modes that are resonant in the central plasma, leading to a significant prolongation of the discharge pulse.

Prolonged antigen persistence within nonterminal late endocytic compartments of antigen-specific B lymphocytes.

Although Ag-specific B lymphocytes can process Ag and express peptide-class II complexes as little as 1 h after Ag exposure, it requires 3-5 days for the immune system to develop a population of Ag-specific effector CD4 T lymphocytes to interact with these complexes. Presently, it is unclear how B cells maintain the expression of cell surface antigenic peptide-class II complexes until effector CD4 T lymphocytes become available. Therefore, we investigated B cell receptor (BCR)-mediated Ag processing and presentation by normal B lymphocytes to determine whether these cells have a mechanism to prolong the cell surface expression of peptide-class II complexes derived from the processing of cognate AG: Interestingly, after transit of early endocytic compartments, internalized Ag-BCR complexes are delivered to nonterminal late endosomes where they persist for a prolonged period of time. In contrast, Ags internalized via fluid phase endocytosis are rapidly delivered to terminal lysosomes and degraded. Moreover, persisting Ag-BCR complexes within nonterminal late endosomes exhibit a higher degree of colocalization with the class II chaperone HLA-DM/H2-M than with the HLA-DM/H2-M regulator HLA-DO/H2-O. Finally, B cells harboring persistent Ag-BCR complexes exhibit prolonged cell surface expression of antigenic peptide-class II complexes. These results demonstrate that B lymphocytes possess a mechanism for prolonging the intracellular persistence of Ag-BCR complexes within nonterminal late endosomes and suggest that this intracellular Ag persistence allows for the prolonged cell surface expression of peptide-class II complexes derived from the processing of specific AG:

Involvement of MIIC-like late endosomes in B cell receptor-mediated antigen processing in murine B cells.

Currently, the involvement of classical vs novel endocytic compartments in the phenomenon of B cell receptor (BCR)-mediated Ag processing is a matter of considerable debate. In murine B cells, class II vesicles (CIIV) represent a novel endocytic compartment involved in BCR-mediated Ag processing and class II peptide loading. Alternatively, in human B cells, the MHC class II-enriched compartment (MIIC) represents a lysosome (L)-like endocytic compartment that appears to be involved in this process. Presently, the relationship between CIIV, MIIC, and classical endosomes and L remains to be determined. Using density gradient centrifugation, a subcellular compartment morphologically and immunologically similar to human MIIC has been identified, isolated, and characterized in murine B cells. These MIIC-like vesicles represent a population of class II-positive late endosomes (LE) and are distinct from CIIV. MIIC-like LE are uniquely marked by the thiol protease cathepsin B, and along with mature L, appear to be the major repository of DM molecules in these cells. Importantly, both MIIC-like LE and CIIV isolated from Ag-pulsed B cells contain BCR-internalized Ag as well as antigenic peptide-class II complexes.

Delivery of B cell receptor-internalized antigen to endosomes and class II vesicles.

B cell receptor (BCR)-mediated antigen processing is a mechanism that allows class II-restricted presentation of specific antigen by B cells at relatively low antigen concentrations. Although BCR-mediated antigen processing and class II peptide loading may occur within one or more endocytic compartments, the functions of these compartments and their relationships to endosomes and lysosomes remain uncertain. In murine B cells, at least one population of class II- containing endocytic vesicles (i.e., CIIV) has been identified and demonstrated to be distinct both physically and functionally from endosomes and lysosomes. We now demonstrate the delivery of BCR-internalized antigen to CIIV within the time frame during which BCR-mediated antigen processing and formation of peptide-class II complexes occurs. Only a fraction of the BCR-internalized antigen was delivered to CIIV, with the majority of internalized antigen being delivered to lysosomes that are largely class II negative. The extensive colocalization of BCR-internalized antigen and newly synthesized class II molecules in CIIV suggests that CIIV may represent a specialized subcellular compartment for BCR-mediated antigen processing. Additionally, we have identified a putative CIIV-marker protein, immunologically related to the Igalpha subunit of the BCR, which further illustrates the unique nature of these endocytic vesicles.

HLA-DM is localized to conventional and unconventional MHC class II-containing endocytic compartments.

HLA-DM molecules remove invariant (Ii) chain peptides from newly synthesized MHC class II complexes. Their localization may thus delineate compartments, e.g., MIIC, specialized for loading peptides onto class II molecules. In murine A20 B cells, however, DM is not restricted to specialized endosomal class II-containing vesicles (CIIV). Although DM was found in CIIV, it was also found throughout the endocytic pathway, principally in lysosomes devoid of class II molecules. In human lymphoblasts, HLA-DM was found in structures indistinguishable from late endosomes or lysosomes, although in these cells the lysosomes contained MHC class II molecules. Thus, the distribution of HLA-DM does not necessarily identify specialized class II compartments. Many "MIIC" may represent conventional lysosomes that accumulate MHC class II and HLA-DM in a number of cell types.

Transient accumulation of new class II MHC molecules in a novel endocytic compartment in B lymphocytes.

Endocytosis of antigen by antigen-presenting cells results in the production of peptides that bind to newly synthesized class II molecules of the major histocompatibility complex. A new population of class II-enriched vesicles has been discovered in B lymphocytes that accumulate internalized antigen but are distinct from endosomes and lysosomes. These vesicles also transiently accumulate newly synthesized class II and class II-peptide complexes and appear to be a compartment specialized for the transport and loading of class II molecules.

The invariant chain is required for intracellular transport and function of major histocompatibility complex class II molecules.

The major histocompatibility complex (MHC) class II-associated invariant chain (Ii) is thought to act as a chaperone that assists class II during folding, assembly, and transport. To define more precisely the role of Ii chain in regulating class II function, we have investigated in detail the biosynthesis, transport, and intracellular distribution of class II molecules in splenocytes from mice bearing a deletion of the Ii gene. As observed previously, the absence of Ii chain caused significant reduction in both class II-restricted antigen presentation and expression of class II molecules at the cell surface because of the intracellular accumulation of alpha and beta chains. Whereas much of the newly synthesized MHC molecules enter a high molecular weight aggregate characteristic of misfolded proteins, most of the alpha and beta chains form dimers and acquire epitopes characteristic of properly folded complexes. Although the complexes do not bind endogenously processed peptides, class II molecules that reach the surface are competent to bind peptides added to the medium, further demonstrating that at least some of the complexes fold properly. Similar to misfolded proteins, however, the alpha and beta chains are poorly terminally glycosylated, suggesting that they fail to reach the Golgi complex. As demonstrated by double label confocal and electron microscope immunocytochemistry, class II molecules were found in a subcompartment of the endoplasmic reticulum and in a population of small nonlysosomal vesicles possibly corresponding to the intermediate compartment or cis-Golgi network. Thus, although alpha and beta chains can fold and form dimers on their own, the absence of Ii chain causes them to be recognized as "misfolded" and retained in the same compartments as bona fide misfolded proteins.

Cytoplasmic domain heterogeneity and functions of IgG Fc receptors in B lymphocytes.

B lymphocytes and macrophages express closely related immunoglobulin G (IgG) Fc receptors (Fc gamma RII) that differ only in the structures of their cytoplasmic domains. Because of cell type-specific alternative messenger RNA splicing, B-cell Fc gamma RII contains an insertion of 47 amino acids that participates in determining receptor function in these cells. Transfection of an Fc gamma RII-negative B-cell line with complementary DNA's encoding the two splice products and various receptor mutants indicated that the insertion was responsible for preventing both Fc gamma RII-mediated endocytosis and Fc gamma RII-mediated antigen presentation. The insertion was not required for Fc gamma RII to modulate surface immunoglobulin-triggered B-cell activation. Instead, regulation of activation involved a region of the cytoplasmic domain common to both the lymphocyte and macrophage receptor isoforms. In contrast, the insertion did contribute to the formation of caps in response to receptor cross-linking, consistent with suggestions that the lymphocyte but not macrophage form of the receptor can associate with the detergent-insoluble cytoskeleton.

Endocytosis of antigen, anti-idiotype, and anti-immunoglobulin antibodies and receptor re-expression by murine B cells.

The endocytosis of Ag mediated by membrane-associated Ig (mIg) molecules has been spectrophotometrically monitored using a cell line (2C3) specific for the hapten phthalate (Xmp) and employing conjugates of Xmp and horseradish peroxidase (HRP) as the labeled ligand. Approximately 50% of both Xmp-HRP, or the larger ligand, Xmp-keyhole limpet hemocyanin-HRP, are internalized rapidly, reaching an initial plateau by 30 min. The rate of endocytosis of anti-idiotype-HRP is similar to the rates that were observed for the hapten-bearing ligands, while a slower rate of endocytosis of anti-Ig-HRP was observed. The percent of ligand bound that is internalized and the rate of endocytosis appear to be largely independent of the size and amount of ligand bound per cell. However, mIg-mediated endocytosis is markedly reduced when mIg-ligand complexes are more extensively cross-linked by the binding of a second antibody. In addition to the initial rapid phase of endocytosis, there is a prolonged phase during which more of the bound ligand is internalized, and up to 90% of the internalized ligand is degraded. Re-expression of Ag-binding receptors by the 2C3 cells is independent of new protein synthesis and is accomplished in part by the translocation of a presynthesized pool of mIg molecules from the cytoplasm to the plasma membrane of the cell. The kinetics of endocytosis of HRP-labeled anti-Ig antibodies by BALB/c splenic B-lymphocytes and other B-lymphocyte cell lines is very similar to the endocytosis of Ag and anti-idiotype observed with the 2C3 cell line. Light and electron microscopy are also performed to visually confirm that the HRP-labeled ligands are being internalized and to determine the percentage of cells involved in this process. Finally it was determined that the transmembrane and cytoplasmic domains of the mIg molecules are required for endocytosis since the secreted form of the molecule (which lacks these domains) fails to mediate the internalization of bound ligand.

Time and financial analysis of an academic general internal medicine unit.

A detailed time and financial analysis of an academic general internal medicine unit was used to examine financial, educational, and research issues. The residents' outpatient service possessed the greatest patient visit and revenue capacity, but revenue recovery was limited by low productivity and collection rate. Outpatient revenue production could be improved but would still be less than current inpatient revenues. Full financial self-sufficiency would require improvements in several aspects of revenue production and would severely limit faculty time for teaching, personal study, and research. Indirect financial contributions to the medical center through hospitalizations and referrals dwarfed direct revenues. Several strategies for academic general internal medicine units to achieve financial and academic survival are possible, each with its own set of trade-offs. Because local circumstances differ, strategies and outcomes are likely to vary among units.

Lack of effect of vitamin E therapy on the anemia of patients receiving hemodialysis.

We conducted a prospective, randomized, double-blind therapeutic trial of vitamin E as an erythropoietic agent in a group of patients with chronic renal failure who were undergoing chronic hemodialysis. Sixteen patients received 400 IU of vitamin E (d-alpha-tocopheryl acetate) by mouth twice daily and 19 patients received a placebo twice daily for 20 wk. The serum vitamin E concentration increased from 1.3 to 2.6 mg/dl in the treated group and decreased from 1.3 to 1.1 in the placebo group. For the treated group the initial hematocrit was 24.8 +/- 3.0 (mean +/- SD) and the final hematocrit was 25.8 +/- 3.8. For the placebo group the initial hematocrit was 24.9 +/- 3.0 and the final hematocrit was 23.5 +/- 2.7. The treated group received a total of 40 blood transfusions, and the placebo group received a total of 35 blood transfusions. Thus, vitamin E had no effect on the anemia or transfusion requirements of patients undergoing chronic hemodialysis for chronic renal failure.

Cost-effectiveness of thyroid function tests.

The cost-effectiveness of thyroid function tests (serum thyroxine concentration, triiodothyronine [T3]-resin uptake, free thyroxine index, serum T3, and serum thyrotropin concentration) was assessed in 135 ambulatory patients suspected of hypothyroidism or hyperthyroidism who did not have a history of thyroid disease requiring medication or thyroid surgery within the preceding two years. Of patients with five or more signs and symptoms compatible with thyroid dysfunction, 50.0% had biochemical abnormalities substantiating hypothyroidism or hyperthyroidism, while only 1.5% of patients with fewer than two signs and symptoms had either disease. The cost of thyroid function tests was twice as much per patient evaluated by residents as for those evaluated by faculty physicians. These results suggest that interventions to reduce the number and type of tests in patients without multiple signs and symptoms of thyroid disease could improve the cost-effective use of these tests.

Status of vitamin E as an erythropoietic factor.

There is now convincing evidence that vitamin E is a specific erythropoietic factor for nonhuman primates and swine. There is no evidence, however, that vitamin E is normally required as an erythropoietic factor for humans and many species of animals. We propose that the lack of a requirement for vitamin E in erythropoiesis in humans is due to a metabolic adaptation that circumvents the need for the role that the vitamin otherwise would serve. There is reason to believe that this metabolic adaptation is deranged in patients with protein-calorie malnutrition. These patients respond with reticulocytosis and a limited increase in hemoglobin concentration when vitamin E is given before their metabolic derangement is reversed by correcting their other nutritional deficiencies. Given this information, we may predict that other acquired or congenital abnormalities of metabolism could impair the adaptation that circumvents the role of vitamin E in erythropoiesis. Therefore, vitamin E should be viewed as a potential erythropoietic factor for humans, and it should receive further carefully controlled therapeutic trials in patients with anemia of obscure etiology, particularly in those with erythroid hyperplasia and unexplained ineffective erythropoiesis.