These results are in broad agreement with previous studies on human HL-60 cell differentiation , in which the authors described the presence of rolling cells (which were able to roll at velocities comparable with those achieved for untreated cells). Although the authors also showed the presence of cells exhibiting circular and/or spiral motion, no attempt was made to analyse the rolling behaviour of these cells. With the present study, we have shown that the ability of DMSO-treated cells to roll is markedly reduced as they undergo terminal differentiation. The results also suggest that DMSO can induce differentiation and that this is accompanied by a reduction in the ability of cells to roll.
In addition to the dynamic nature of HL-60 cell rolling, we observed striking differences in particle velocity. In the presence of S1P or DMSO, cells moved at relatively low speeds, whereas the rolling HL-60 cells exposed to LPS moved at higher average velocities. These differences may reflect alterations to surface protein expression as a result of S1P or DMSO exposure. For example, in HL-60 cells exposed to DMSO, we observed the transient increase in PSGL-1 expression that occurs in other cell types. As PSGL-1 is known to bind to P-selectin and endothelial cells have been shown to express P-selectin on their surface , we surmise that the concomitant increase in PSGL-1 expression facilitates HL-60 cell rolling. Indeed, it has been reported that HL-60 cells express P-selectin on their surface after exposure to DMSO or TNF-α [22, 34]. In contrast to PSGL-1, L-selectin expression is known to remain constant in HL-60 cells over the course of the exposure . HL-60 cells exposed to S1P, on the other hand, do not display a similar phenomenon.
Teams occasionally need to move APs from the field. This might be due to seasonal changes in the environment, the addition of new features or addressing new applications. Sites that have known problems with APs or users of a particular type of AP should move that type. Moving APs in periods of heavy usage, such as periods around holiday seasons or peak periods, could cause a performance problem. 827ec27edc