Albumin stimulation of eosinophil migration involves PI3-kinases and is associated with diminished eosinophil CD49d and CD49f expression.

BACKGROUND

Albumin is known to induce chemokinesis and facilitate chemotaxis of human granulocytes in the Boyden chamber assay, but its mechanisms of action remain obscure. We have previously found that IL-2 inhibits albumin-stimulated eosinophil migration. The aim of this study was to identify the mechanisms behind the effects of albumin and IL-2 on the migration of human eosinophils.

METHODS

Purified eosinophils were preincubated with inhibitors of signal transduction molecules before incubation with or without albumin and IL-2. The migration assay was performed in a 48-well microchemotaxis chamber. The effect of albumin and IL-2 on cell size and on the surface expression of adhesion molecules was studied with flow cytometry.

RESULTS

Albumin-stimulated migration was inhibited by the PI3-kinase inhibitors wortmannin and LY-294002, but not by the PKC inhibitor RO-31-8220. IL-2 had no effect after preincubation with wortmannin or LY-294002. In contrast, the inhibitory effect of IL-2 remained after preincubation with RO-31-8220. Albumin increased the cell size as measured by forward scatter, and the expression of CD49d and CD49f decreased after incubation with albumin. IL-2 affected neither the expression of adhesion molecules nor the forward scatter.

CONCLUSIONS

The stimulation of eosinophil migration by albumin is mediated by PI3-kinase, and the increase in cell size caused by albumin indicates activation of the cells. Decreased expression of CD49d and CD49f by albumin may diminish the adhesiveness of the cells, which in turn may facilitate migration. These are novel findings that indicate an active role for albumin in eosinophil migration.