The effect of inhalation of platelet-activating factor on the pulmonary clearance of 99mTc-DTPA aerosol

Potential role of IL-8, platelet-activating factor and TNF-alpha in the sequestration of neutrophils in the lung: effects on neutrophil deformability, adhesion receptor expression, and chemotaxis

The microvasculature of the normal lung contains a pool of sequestered neutrophils, which is markedly enhanced in acute lung inflammation. Lung neutrophil sequestration is determined by the cells' deformability and adhesivity to capillary endothelium, and is a pre-requisite for emigration into the airspaces. We assessed the effect of several pro-inflammatory mediators associated with acute lung inflammation on these factors. Platelet-activating factor, IL-8 and formyl-Met-Leu-Phe (fMLP) induced a marked, but transient reduction in neutrophil deformability. Also, increased surface expression of the beta(2)-integrin and CD11b, and shedding of L-selectin (CD62L) was observed for these stimuli. TNF-alpha in contrast caused a small decrease in cell deformability only after 30 min, and shedding of L-selectin, but no change in CD11b levels. However, TNF-alpha-pretreatment markedly enhanced the fMLP response for cell deformability, CD11b expression and CD62L loss. Moreover, all pre-treatments were found to induce chemokinesis, and all except fMLP, enhanced fMLP-directed chemotaxis. We were able to demonstrate, using specific TNF-alpha receptor antagonists, that the TNF-alpha-induced changes in chemotaxis were mediated through the 55-kDa receptor. Also, inhibitors of the mitogen activated protein (MAP) kinase signaling pathway showed that the p38 MAP kinase pathway was involved for fMLP-directed chemotaxis of TNF-pretreated neutrophils, although activation of the extracellular signal-regulated kinase (ERK) pathway was also seen. These data demonstrate the differential role of pro-inflammatory mediators in controlling neutrophil sequestration and migration, which may orchestrate the severity of the inflammatory response in such respiratory diseases as chronic obstructive pulmonary disease and asthma.

Structure, biologic properties, and expression of surfactant protein D (SP-D)

Surfactant protein D (SP-D) is a member of the family of collagenous host defense lectins, designated collectins. There is increasing evidence that SP-D, like SP-A, is an important component of the innate immune response to microbial challenge, and that it may participate in other aspects of immune and inflammatory regulation within the lung. SP-D binds to glycoconjugates and/or lipid moieties expressed by a wide variety of microorganisms and certain other organic particles, in vitro. Although binding may facilitate microbial clearance through aggregation or other direct effects on the organism, SP-D also has the capacity to modulate leukocyte function, and in some circumstances, to enhance their killing of microorganisms.

Surfactant protein A and surfactant protein D in health and disease

Surfactant protein (SP) A and SP-D are collagenous glycoproteins with multiple functions in the lung. Both of these proteins are calcium-dependent lectins and are structurally similar to mannose-binding protein and bovine conglutinin. Both form polyvalent multimeric structures for interactions with pathogens, cells, or other molecules. SP-A is an integral part of the surfactant system, binds phospholipids avidly, and is found in lamellar bodies and tubular myelin. Initially, most research interest focused on its role in surfactant homeostasis. Recently, more attention has been placed on the role of SP-A as a host defense molecule and its interactions with pathogens and phagocytic cells. SP-D is much less involved with the surfactant system. SP-D appears to be primarily a host defense molecule that binds surfactant phospholipids poorly and is not found in lamellar inclusion bodies or tubular myelin. Both SP-A and SP-D bind a wide spectrum of pathogens including viruses, bacteria, fungi, and pneumocystis. In addition, both molecules have been measured in the systemic circulation by immunologic methods and may be useful biomarkers of disease. The current challenges are characterization of the three-dimensional crystal structure of SP-A and SP-D, molecular cloning of their receptors, and determination of their precise physiological functions in vivo.

Scintigraphical evaluation of alveolar clearance in horses

This study proposed a standardized method for measuring alveolar epithelium membrane permeability in the horse. The normal rate of clearance (%.min-1) from lung into blood of nebulized 99mTc-DTPA has been established for healthy horses (Group A) compared with values obtained with horses suffering from chronic obstructive pulmonary disease (COPD; Group B). The 99mTc-DTPA clearance was measured in the caudoventral (R1) and in the half caudal (R2) parts of the left lung during different time intervals. The two regions aimed to define the influence of the airways on measured clearance (R2 contained proportionally more conducting airways than R1). It was concluded that a comparison of groups of subjects may be performed in R2 and on data collected during a 20 min period. The normal clearance rate in R2 was 1.80 +/- 0.46%.min-1 (T1/2R2 = 40.99 +/- 12.45 min) in Group A. In Group B, a significantly faster 99mTc-DTPA transfer rate was found (4.17 +/- 0.83%.min-1 or T1/2R2 = 17.17 +/- 3.38min). Bronchoalveolar lavage (BAL) suggested that the increased permeability measured in Group B could be the result of lung inflammatory responses. Our results have demonstrated the ability of the 99mTc-DTPA clearance test to detect alveolar epithelial damage in horses. Furthermore, we were able to show that a regional analysis of the alveolar-capillary barrier integrity may be performed satisfactorily in the equine patient.

Appropriate background correction for DTPA aerosol clearance

Measurement of the clearance rate of inhaled aerosols of 99mTc-diethylenetriamine pentaacetic acid (DTPA) from distal airway to pulmonary capillary is a sensitive technique for the detection of lung injury. As the solute diffuses across the blood-gas barrier, the concentration in circulating blood increases, giving rise to a background signal superimposed on the signal from residual DTPA in the airway. Background subtraction is conventionally based on the thigh, but this tissue has the disadvantage in that its composition, in terms of the relative volumes of its extracellular extravascular and intravascular compartments (a ratio of approximately 4:1), is quite different from that of the lung (<1:6). With comparison to the thigh, we examined alternative regions for background, liver, and cranium, which have extravascular-to-intravascular compartment ratios much closer to these for the lung, to determine the most appropriate background for correction of the pulmonary signal. From 1 min after intravenous injection of 99mTc-DTPA, the time-activity curves recorded by a gamma camera over the liver and lung in a group of otherwise normal cigarette smokers decreased up to 30 min after injection, with time courses that could essentially be superimposed on each other; the curve recorded over the thigh with a separate scintillation probe continued to increase. The curve recorded over the cranium had a time course similar to that for the liver and lung. Following aerosol inhalation, the lung clearance rates over the initial 7 min when background subtraction was used, based on the liver, cranium, and thigh were, respectively, 4.9 +/- 2.9, 4.7 +/- 2. 6, and 5.4 +/- 3.4 (SD) %/min, compared with 4.1 +/- 2.2%/min without subtraction. The corresponding values based on 30 min of data were 3.3 +/- 1.4, 3.4 +/- 1.4, 4.2 +/- 2.3, and 2.8 +/- 1. 0%/min. When the liver was used for background, the lung clearance curves were clearly multiexponential, whereas thigh correction tended to give curves that were monoexponential or even convex upward on semilogarithmic axes. With an appropriate region for background, the true shape of a lung curve can be identified, which permits the study of an intervention on the clearance while it is in progress. The intravenous DTPA, required for calibrating the background regions, can be given before inhalation of the tracer.

Airway and alveolar permeability and surface liquid thickness: theory

The thickness of airway surface liquid (ASL) can be calculated as the ratio of the permeability coefficient of an absorbed inert tracer to the percentage rate in which it decreases in content in the airway lumen. The percentage clearance of radiolabeled diethylenetriaminepentaacetic acid (DTPA) from human airways or lungs has been measured many times, with a mean value of 1.04 +/- 0.25 (SD) %/min. Rates of clearance from animal lungs of most species give values of the same order, although they are lower in the sheep and higher in the dog. Permeability coefficients have not been measured simultaneously with percentage clearances and not at all for human tissues. Values for mannitol and sucrose, of which the former gives a permeability coefficient approximately 25% greater than that for sucrose and DTPA in airway tubes and isolated mucosal sheets from experimental animals, give a mean approximately 7.1 x 10(-7) cm/s. This corresponds to thickness of ASl of approximately 20-150 microns for various species. The assumptions underlying this estimate are discussed. It is concluded that ASL thickness in vivo may be considerably greater than in vitro measurements involving rapid freezing of the airway wall. Estimates of alveolar permeability suggest that either it is very considerably lower than that of the airway epithelium, that methods to measure alveolar permeability mainly reflect airway permeability, or both.