We examined the effect of dibutyryl cAMP (dbcAMP) on the expression of LFA-1 (CD11a/CD18), Mac-1 (CD11b/CD18), and VLA-4 (CD49/CD29) and on eosinophilic differentiation of a human leukemia cell line, EoL-1. Dibutyryl cAMP induced eosinophilic differentiation of EoL-1 cells from 6-9 days after the start of culture with down-regulation of CD11a, CD18, and CD49 expression and up-regulation of CD11b expression. Changes in integrin expression, except for CD18, were seen predominantly in the fraction containing eosinophilic granule-positive cells, suggesting that the changes were dependent on eosinophilic differentiation. On the other hand, dbcAMP-induced changes of integrin expression were reversible and were not seen on day 9 when dbcAMP was removed on day 3, whereas eosinophilic differentiation was still present. A combination of G-CSF and TNF-alpha, which also induced eosinophilic differentiation of EoL-1 cells, increased CD11b expression slightly but had no significant effect on the expression of the other integrins. Butyrate and PMA up-regulated CD11b expression without eosinophilic differentiation. The results collectively suggest that the regulation of integrin expression on EoL-1 cells is partly dependent and partly not dependent on eosinophilic differentiation. The possible involvement of protein kinase A and protein kinase C in these changes is suggested.