1. Lipoxin A4 (LXA4) and lipoxin B4 (LXB4) have been evaluated for their capacities to modulate neutrophil (PMN) migration and endothelial cell adherence using compounds prepared by total chemical synthesis. 2. Increased PMN migration was seen with concentrations of LXA4 from 10(-9) mol/l to 10(-7) mol/l. LXA4 was 100-fold less potent than leukotriene B4 (LTB4) and it elicited only one-half of the maximal response of LTB4. 3. The (5S,6S,15S)-isomer of LXA4 induced only a weak migratory response and LXB4 was inactive, suggesting that the activity of LXA4 was stereospecific. 4. Modified chequerboard analysis indicated that LXA4 was a chemokinetic agent. 5. Preincubation of PMN with increasing concentrations of LXA4 induced a very similar dose- and time-dependent inhibition of the subsequent response to 10(-7) mol/l LTB4 or 10(-7) mol/l N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP). The inhibition was observed at 10(-10) mol/l LXA4; the concentration which produced 50% inhibition was 10(-8) mol/l and 100% inhibition of PMN locomotion occurred at 10(-6) mol/l LXA4. 6. The (5S,6S,15S)-isomers of LXA4 and LXB4 were 5- and 100-fold less potent than LXA4, respectively, in suppressing LTB4- or FMLP-induced PMN migration. 7. Preincubation of PMN with LXA4 led to a suppression of calcium mobilization, as assessed by Quin2-AM fluorescence, when the cells were subsequently stimulated under optimal conditions by LTB4 or FMLP. 8. These results suggest that the inhibitory activity of lipoxins may be related to the capacity of these molecules to regulate calcium ion mobilization.

No abstract

Cultured human umbilical vein endothelial cell (EC) monolayers stimulated with 10 ng/ml tumor necrosis factor demonstrate a time-dependent increase in the expression of the vascular cell adhesion molecule-1 (VCAM-1) with maintained maximal expression at 24 h following EC activation. A monoclonal antibody (mAb) directed against VCAM-1 (1G11) significantly inhibited the adhesion of eosinophils, but not neutrophils, to EC, which had been activated by tumor necrosis factor-alpha for 24 h, but only when eosinophils had been pretreated with an mAb directed against the common beta chain of the CD11/CD18 complex. In the absence of pretreatment with anti-CD18, mAb 1G11 had no significant effect on eosinophil adhesion. These results suggest that eosinophils bind to VCAM-1. However, the functional capacity in this model of the eosinophil receptor for VCAM-1 is likely to be minor compared with the activity of the CD11/CD18 leukocyte adhesion molecules.

The adhesion of lymphocytes to vascular endothelium is the first step in their passage from the blood into inflammatory tissues. By modulating endothelial cell (EC) adhesiveness for lymphocytes, cytokines may regulate lymphocyte accumulation and hence the nature and progression of inflammatory responses. IL-1, TNF, IFN-gamma, and IL-4 each increase EC adhesiveness for T cells when used alone in adhesion assays in vitro. As cytokines are more likely to act in combination at sites of inflammation in vivo, we have studied the stimulating effect of different combinations of cytokines on EC adhesiveness for T cells and polymorphonuclear leukocytes (PMN). Acting alone IL-1, TNF, IFN-gamma, and IL-4 each significantly enhanced EC adhesiveness for T cells (p less than 0.005), whereas only IL-1 (p less than 0.005) and TNF (p less than 0.005) but not IFN-gamma or IL-4 significantly enhanced adhesiveness for PMN. When EC were stimulated with optimal concentrations of TNF in combination with IL-4 or IFN-gamma, there was a significant further increase in adhesiveness for T cells (p less than 0.003), but not PMN, over that seen with TNF alone. The additive effect of TNF and IL-4 was more marked than that of TNF and IFN-gamma. Although approximately equal proportions of T cells and PMN bound to TNF-stimulated EC, nearly double the proportion of T cells compared with PMN bound EC preincubated with TNF and IL-4 together. A similar interaction with IL-4 or IFN-gamma was exhibited by lymphotoxin. mAb-inhibition studies indicated that the extra increase in binding caused by stimulating EC with TNF and IL-4 in combination was mediated by VCAM-1 whereas that caused by stimulating with TNF and IFN-gamma in combination was substantially mediated through leukocyte function-associated Ag-1- and VCAM-1-independent mechanisms. These observations suggest that whereas IL-1 and TNF alone are unselective in terms of leukocyte adhesion to EC, the combination of TNF (or LT) with IL-4 or IFN-gamma may be of key importance in determining the recruitment of a lymphocyte-predominant infiltrate in immune mediated inflammation, and in initiating the transition from acute to chronic inflammation.

We have compared the adhesion of 51Cr-labeled eosinophils and neutrophils to cultured human umbilical vein endothelial cell (EC) monolayers that have been stimulated with IL-1, TNF, or LPS. Each agent stimulated the adhesion to EC of both eosinophils and neutrophils in a similar dose- and time-dependent manner. F(ab')2 fragments of mAb 1.2B6 (anti-endothelial leukocyte adhesion molecule (ELAM)-1) and mAb 6.5B5 (anti-intercellular adhesion molecule (ICAM)-1) each inhibited partially, and to a similar extent, eosinophil and neutrophil adhesion to EC monolayers prestimulated with TNF (10 ng/ml) for 6 h. Greater inhibition of both eosinophil and neutrophil adhesion was achieved by combining the effects of mAb 1.2B6 with either mAb 6.5B5 or mAb TS1/18 (anti-CD18). These observations indicate that both ELAM-1 and ICAM-1 are involved in the adhesion of eosinophils and neutrophils to EC stimulated with TNF. In order to determine whether these molecules are expressed in vivo during allergen-induced late phase allergic responses in the skin, human skin biopsies were examined at 6 h after Ag or saline challenge with the use of an alkaline phosphatase-staining technique. Both ELAM-1 and ICAM-1 were expressed with greater intensities in Ag-challenged biopsies, suggesting that these molecules may be involved in granulocyte recruitment in vivo. The similarities we have established between mechanisms of eosinophil and neutrophil adhesion to cytokine-stimulated EC suggests that factors other than differential leukocyte-EC adhesion may be responsible for the selective accumulation of eosinophils at sites of allergic inflammation.