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Differential Effects of Two Fluorescent Probes on Macrophage Migration as Assessed by Manual and Automated Methods]

Fluorescent probes have been utilized to label leukocytes for both in vivo and in vitro studies of cell migration; however, the effects of such probes on migration have not been determined. The aim of this study was to examine the effects of two commonly used fluorescent probes on leukocyte chemotaxis. J774 macrophages were labeled with either calcein-acetoxymethyl ester (calcein-AM) or 2′,7′-bis-(2-carboxyethyl)-5-(and 6)-carboxyfluorescein, acetomethyl ester (BCECF-AM), then assayed for their ability to migrate to zymosan-activated serum (ZAS). Cell migration was quantified by two methods: visual counting of cells and measuring cell fluorescence. Using the cell counts, comparison of unlabeled and fluorescently labeled macrophages demonstrated that BCECF-AM decreased the number of cells responding to ZAS, while calcein-AM had essentially no effect. Neither probe significantly affected the number of cells migrating to medium alone. The inhibitory effects of BCECF-AM on cell migration increased with probe concentration (0.1-1.0 microM) and cell fluorescence. Cell viability was unaffected by either probe. In contrast to the results obtained by visual counting, measuring fluorescence of migrated cells did not reveal a significant difference between the chemotactic response of macrophages labeled with BCECF-AM and those labeled with calcein-AM. These experiments indicated that fluorescent probes can affect the chemotactic response and that inhibitory activity of these probes may not be detected when chemotaxis is quantified solely by automated methods.

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Glycoprotein-340 Binds Surfactant Protein-A (SP-A) and Stimulates Alveolar Macrophage Migration in an SP-A-Independent Manner

Glycoprotein-340 (gp-340) was first identified as a surfactant protein (SP)-D–binding molecule purified from lung lavage of patients with alveolar proteinosis (Holmskov, et al., J. Biol. Chem. 1997;272:13743). In purifying SP-A from proteinosis lavage, we isolated a protein that copurifies with SP-A and SP-D and that was later found by protein sequencing to be gp-340. We have shown that soluble gp-340 binds SP-A in a calcium-dependent manner independent of the lectin activity of SP-A. To examine the functional significance of this interaction, we tested the ability of soluble gp-340 to block SP-A binding to and stimulation of the chemotaxis of alveolar macrophages. We found that gp-340 does not affect the binding of SP-A to alveolar macrophages over a wide range of SP-A concentrations, nor does it inhibit the ability of SP-A to stimulate macrophage chemotaxis. We also found that gp-340 alone stimulates the random migration (chemokinesis) of alveolar macrophages in a manner independent of SP-A–stimulated chemotaxis. These results suggest that gp-340 is not a cell-surface receptor necessary for SP-A stimulation of chemotaxis, and show that gp-340 can directly affect macrophage function.

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A rapid, multiwell colorimetric assay for chemotaxis

This paper describes a colorimetric assay for the rapid quantification of chemotaxis in multiple samples. In this assay, cells that have migrated through polycarbonate membrane filters are collected onto the bottom wells of a chemotaxis chamber after centrifugation then the number of viable cells collected in the bottom well is quantified by measurement of the reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenol tetrazolium bromide (MTT). The degree of MTT reduction, which corresponds to the relative cell number, is measured automatically with an ELISA reader. The MTT method of quantitation is as sensitive as the standard manual method, is especially useful for large numbers of samples and requires no specialized laboratory equipment.

Shi Y, Kornovski BS, Savani R, Turley EA.

Manitoba Institute of Cell Biology, University of Manitoba, Winnipeg, Canada.

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