Regulation of ICAM‐3 and other adhesion molecule expressions on eosinophils
in vitro. Effects of dexamethasone

Background: ICAM‐3 has been recently identified as the third leukocyte‐function associated‐1 (LFA‐1) ligand. ICAM‐3 is expressed in eosinophils, but its regulation has not been studied. The objective of this study was to investigate the differential expression of ICAM‐3 and other adhesion molecules (AM) on the surface of eosinophils. We also evaluated the effects of dexamethasone on AM expression. Methods: Normodense eosinophils were isolated from peripheral blood and incubated with calcium ionophore A23187 (calcimycin) with and without dexamethasone. Expression of AM was assessed by flow cytometry and expressed as fluorescence mean intensity (FMI). Results: Peripheral blood eosinophils constitutively expressed low levels of ICAM‐1 and ICAM‐2 (<10 FMI), moderate levels (10–50 FMI) of CD29 and L‐selectin, and high levels (>50 FMI) of ICAM‐3, LFA‐1, and Mac‐1. Calcium ionophore (1 μM) significantly increased Mac‐1 and ICAM‐1 expression at 6 and 24 h. L‐selectin expression decreased at 6 and 24 h, but ICAM‐2, ICAM‐3, LFA‐1, and CD29 expression did not show any significant change after calcium ionophore stimulation. Dexamethasone decreased ICAM‐3 and increased L‐selectin basal expression, and it caused a dose‐related inhibition of calcium ionophore‐induced ICAM‐1 expression. Conclusions: These findings suggest that some AM, such as ICAM‐1, Mac‐1, and L‐selectin, may be involved in adhesion during eosinophil activation and that glucocorticoids may prevent airway inflammation by regulating the expression of AM in eosinophils. The role of ICAM‐3, a leukocyte AM highly expressed in resting eosinophils, remains to be clarified.