Utility of radioisotopic filtration markers in chronic renal insufficiency: simultaneous comparison of 125I-iothalamate, 169Yb-DTPA, 99mTc-DTPA, and inulin. The Modification of Diet in Renal Disease Study

Assessment of glomerular filtration rate (GFR) with inulin is cumbersome and time-consuming. Radioisotopic filtration markers have been studied as filtration markers because they can be used without continuous intravenous (IV) infusion and because analysis is relatively simple. Although the clearances of 99mTc-diethylenetriamine-pentaacetic acid (DTPA), 169Yb-DTPA, and 125I-iothalamate have each been compared with inulin, rarely has the comparability of radioisotopic filtration markers been directly evaluated in the same subject. To this purpose, we determined the renal clearance of inulin administered by continuous infusion and the above radioisotopic filtration markers administered as bolus injections, simultaneously in four subjects with normal renal function and 16 subjects with renal insufficiency. Subjects were studied twice in order to assess within-study and between-study variability. Unlabeled iothalamate was infused during the second half of each study to assess its effect on clearances. We found that renal clearance of 125I-iothalamate and 169Yb-DTPA significantly exceeded clearance of inulin in patients with renal insufficiency, but only by several mL.min-1.1.73m-2. Overestimation of inulin clearance by radioisotopic filtration markers was found in all normal subjects. No differences between markers were found in the coefficient of variation of clearances either between periods on a given study day (within-day variability) or between the two study days (between-day variability). The true test variability between days did not correlate with within-test variability. We conclude that the renal clearance of 99mTc-DTPA, 169Yb-DTPA, or 125I-iothalamate administered as a single IV or subcutaneous injection can be used to accurately measure GFR in subjects with renal insufficiency; use of the single injection technique may overestimate GFR in normal subjects.     

An antigen-independent contact mechanism as an early step in T cell- proliferative responses to dendritic cells

Dendritic cells bearing antigen efficiently aggregate and stimulate antigen-specific T cells. We describe an experimental model in which an initial, apparently antigen-independent binding step is followed by ligation of the TCR. The model is the polyclonal response to mAb to the CD3 portion of the TCR complex. Epidermal and thymic dendritic cells utilize low levels of Fc receptors to present the anti-CD3 mAb and induce mitogenesis. Within 3 h of coculture, most of the dendritic cells have formed clusters with the resting T lymphocytes, and these clusters are the site for subsequent DNA synthesis and cell growth. However, the binding of dendritic cells to T cells proceeds as efficiently in the absence of anti-CD3 as in its presence, and anti-FcR mAb does not block. CD3 and Fc receptors are essential for the subsequent mitogenesis response in dendritic-T cell clusters. Because an exogenous ligand for the TCR does not seem to be required for the extensive polyclonal clustering of resting lymphocytes to dendritic cells, we suggest that an antigen-independent mechanism mediates the initial interaction. This clustering seems essential for T cell growth since we do not detect, in two-chamber experiments, soluble lymphocyte-activating factors that originate from dendritic-T cell aggregates and that activate anti-CD3-coated T cells.     

Correlations among time and frequency domain measures of heart period variability two weeks after acute myocardial infarction.

Seven hundred fifteen participants from a multicenter natural history study of acute myocardial infarction were studied (1) to determine the correlations among time and frequency domain measures of heart period variability, (2) to determine the correlations between the measures of heart period variability and previously established post-infarction risk predictors, and (3) to determine the predictive value of time domain measures of heart period variability for death during follow-up after acute myocardial infarction. Twenty-four hour electrocardiographic recordings obtained 11 +/- 3 days after acute myocardial infarction were analyzed and 11 measures of heart period variability were computed. Each of 4 bands in the heart period power spectrum had 1 or 2 corresponding variables in the time domain that correlated with it so strongly (r greater than or equal to 0.90) that the variables were essentially equivalent: ultra low frequency power with SDNN* and SDANN index,* very low frequency power and low-frequency power with SDNN index,* and high-frequency power with r-MSSD* and pNN50.* As expected from theoretical considerations, SDNN and the square root of total power were almost perfectly correlated. Correlations between the time and frequency domain measures of heart period variability and previously identified postinfarction risk predictors, e.g., left ventricular ejection fraction and ventricular arrhythmias, are remarkably weak. Time domain measures of heart period variability, especially those that measure ultra low or low-frequency power, are strongly and independently associated with death during follow-up. * Defined in Table II.     

Statins—Treatment Option for Central Nervous System Autoimmune Disease?

Statins, inhibitors of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase, are well-established agents to lower cholesterol levels and prevent cardiovascular morbidity. Independent of their lipid-lowering properties, statins have been shown to exert pleiotropic immunomodulatory effects in various animal models of human autoimmune disease. In experimental autoimmune encephalomyelitis, a murine model for multiple sclerosis, statins prevented disease onset and even reversed paralysis when treatment was initiated after experimental autoimmune encephalomyelitis was fully established. Furthermore, well-tolerated oral statins were recently shown to exert synergistic benefit in experimental autoimmune encephalomyelitis in combination with existing agents for multiple sclerosis therapy. Based primarily on these encouraging results, statins are now being tested in clinical trials as a mono-therapy for multiple sclerosis, as well as in combination with approved disease-modifying therapies.     

The anatomy of peripheral lymphoid organs with emphasis on accessory cells: Light-microscopic immunocytochemical studies of mouse spleen,lymph node,and peyer's patch

Antigen, lymphocytes, and accessory cells interact within peripheral lymphoid organs to generate immunity. Two cell types have been studied for accessory function in culture: mononuclear phagocytes and nonphagocytic Ia-rich dendritic cells. The monoclonal antibodies which have been used to study isolated murine macrophages (MØ) and dendritic cells (DC) include α-macrophage (F4/80, M1/70), α-dendritic cell (33D1), α-Fc receptor (2.4G2), and α-Ia (B21-2) reagents. In this paper, the antibodies have been used to stain accessory cells in cryostat sections of mouse spleen, lymph node, and Peyer's patch. Each organ is known to contain subregions that are rich in either macrophages, B cells, or T cells. We found that the accessory cells in each subregion had a different phenotype. (1) Macrophage-rich regions: Macrophages that lined the site of antigen delivery (marginal zone of spleen, around afferent lymphatics of node, and below the epithelium of Peyer's patch) were stained with M1/70 but not with F4/80. F4/80 was abundant on macrophages in other sites: spleen red pulp, node medulla, and around Peyer's patch efferent lymphatics. (2) B-lymphocyte-rich follicles: Follicular dendritic cells, which retain immune complexes extracellularly, are concentrated on the outer aspect of the germinal center. This region stained strongly with α-Fc receptor antibody 2.4G-2, but not with M1/70, F4/80, or 33D1. (3) T areas: The interdigitating cells of T areas have been linked to isolated dendritic cells. Irregular Ia-rich cells were distributed uniformly in the T areas of each organ. However, staining with 33D1 was not detected and was restricted to foci of nonphagocytic cells at the spleen red/white pulp junction. F4/80, M1/70 or 2.4G2 also did not stain the T area, except for the region close to splenic central arteries. Therefore the principal surface markers and location of the candidate accessory cells in murine lymphoid organs are M1/70⁺ macrophages at the site of antigen entry; F4/80⁺ macrophages around regions of lymphocyte efflux; germinal center dendritic cells, which may be rich in 2.4G2; and Ia-rich interdigiting cells in the T area.     

SIGN-R1, a novel C-type lectin expressed by marginal zone macrophages in spleen,mediates uptake of the polysaccharide dextran

The marginal zone macrophages of the spleen are implicated in the clearance of polysaccharides, but underlying mechanisms need to be pinpointed. SIGN-R1 is one of five recently identified mouse genes that are homologous to human DC-SIGN and encode a single, external, C-terminal C-type lectin domain. We find that a polyclonal antibody to a specific SIGN-R1 peptide reacts primarily and strongly with a subset of macrophages in the marginal zone of spleen and lymph node medulla. In both sites, SIGN-R1 exists primarily in an aggregated form, resistant to dissociation into monomers upon boiling in SDS under reducing conditions. Upon transfection into three different cell lines, high-mol.-wt forms bearing SIGN-R1 are expressed, as well as reactivity with ER-TR9, a mAb previously described to react selectively with marginal zone macrophages. SIGN-R1-expressing macrophages preferentially sequester dextrans following i.v. injection. Likewise, when phagocytic cells are enriched from spleen and tested in culture, dextran is selectively endocytosed by a subset of very large SIGN-R1(+) cells representing approximately 5% of total released macrophages. Uptake of FITC-dextran by these macrophages in vivo and in vitro is blocked by ER-TR9 and polyclonal anti-SIGN-R1 antibodies. Following transfection with SIGN-R1, cell lines become competent to endocytose dextrans. The dextran localizes primarily to compartments lacking transferrin receptor and the LAMP-1 CD107a panlysosomal antigen. Therefore, SIGN-R1 mediates the uptake of dextran polysaccharides, and it is predominantly expressed in the macrophages of the splenic marginal zone and lymph node medulla.