Imaging infections with antibodies. A quantitative autoradiographic analysis.

Radiolabeled IgG has recently been demonstrated to effectively image infections. A potential but unproven mechanism for this localization is the specific binding of IgG to Fc receptors on the surface of inflammatory cells in infections. In an animal model of soft tissue infection, quantitative autoradiography was used to measure 125I-labeled IgG and albumin in tissues with a spatial resolution sufficient to associate these proteins with cellular morphology. Gamma camera images at 24 h localized the infection with target-to-background ratios of 2.2 +/- 0.5 for IgG and 2.3 +/- 1.0 for albumin (mean +/- SD). Using quantitative autoradiography at 1 h post-injection, significantly higher concentrations were found in infected thighs of 2-4% of initial plasma concentrations (CPo) as compared to 0.2-0.3% of CPo in noninfected thighs (P less than 0.05); at 24 h post-injection, higher concentrations (7-8% of CPo) were found in infected thighs. Radiolabeled proteins were not inflammatory cell associated and were localized primarily within the edematous interstitial spaces of the infection.

Endothelial communication. State of the art lecture.

By virtue of its location at the interface of flowing blood and vascular tissue, the endothelial cell monolayer is in a unique position for interactions with soluble and cellular elements of the blood on one side and with component cells of the vascular tissue on the other. This brief review outlines humoral and contact-mediated endothelial communication with other cells, particularly the resident cells of the vessel wall. Evidence for gap junctional communication channels between endothelium and vascular cells is summarized and discussed in relation to endothelial ion channel activity. Myoendothelial gap junctional communication is proposed as a mechanism involved in vasorelaxation, either independent of or in concert with secreted endothelium-derived relaxing factor(s).

Absolute quantitative autoradiography of low concentrations of [125I]-labeled proteins in arterial tissue.

We developed a method for absolute quantitative autoradiographic measurement of very low concentrations of [125I]-labeled proteins in arterial tissue using Kodak NTB-2 nuclear emulsion. A precise linear relationship between measured silver grain density and isotope concentration was obtained with uniformly labeled standard sources composed of epoxy-embedded gelatin containing glutaraldehyde-fixed [125I]-albumin. For up to 308-day exposures of 1 micron-thick tissue sections, background grain densities ranged from about two to eight grains/1000 micron 2, and the technique was sensitive to as little as about one grain/1000 micron 2 above background, which correspond to a radioactivity concentration of about 2 x 10(4) cpm/ml. A detailed statistical analysis of variability was performed and the sum of all sources of variation quantified. The half distance for spatial resolution was 1.7 micron. Both visual and automated techniques were employed for quantitative grain density analysis. The method was illustrated by measurement of in vivo transmural [125I]-low-density lipoprotein [( 125I]-LDL) concentration profiles in de-endothelialized rabbit thoracic aortic wall.

Endothelial cell perturbation and low-density lipoprotein. Quantitative autoradiography.

The focal entry and accumulation of LDL within the arterial wall of the normal animal may represent an early stage in the development of the atherosclerotic plaque. Concentrations of LDL 10 to 100 times normal medial concentrations might be difficult to clear from the arterial wall, permitting accumulation of lipid. Elevated LDL concentrations, in proximity to smooth muscle cells, appear to stimulate SMC proliferation. High LDL concentrations might also enhance mononuclear cell adhesion to endothelium. Since LDL has a high affinity for heparin and heparin for growth factors, LDL accumulation may be a mechanism for the concentration of such materials in the intima. The observation of markedly enhanced macromolecular permeability foci could be related to several potential mechanisms of initiation of atherosclerosis. This observation is of particular note when the focal occurrence of atherosclerosis is considered. Although atherosclerosis is seen as a generalized thickening of the intima, it is the focal narrowing of the lumen that is often responsible for the stenosis which produces symptoms such as angina or myocardial infarction.

Local variation in arterial wall permeability to low density lipoprotein in normal rabbit aorta.

Normal rabbits were injected intravenously with horseradish peroxidase (HRP) and 125I-labeled human low density lipoprotein (LDL), and the aortas were perfusion-fixed. Subsequent visualization of HRP in the aortas was produced by reaction of the tissue with diaminobenzidine and hydrogen peroxide. The luminal surface of the aortas showed many small punctate foci of brown reaction product to the HRP, which represented penetration of the HRP into the vessel wall. The foci were scattered over the luminal surface, and most of the focal areas were less than 1 mm in diameter. The concentration of LDL was up to 47 times greater in these focal areas than in surrounding noncolored regions not showing increased permeability to HRP. Small circumscribed foci of heightened permeability to LDL may predispose to the local accumulation of lipid and ultimately to the formation of atherosclerotic plaques.